diff options
Diffstat (limited to 'kernel/printk')
| -rw-r--r-- | kernel/printk/Makefile | 1 | ||||
| -rw-r--r-- | kernel/printk/printk_ringbuffer.c | 1687 | ||||
| -rw-r--r-- | kernel/printk/printk_ringbuffer.h | 399 |
3 files changed, 2087 insertions, 0 deletions
diff --git a/kernel/printk/Makefile b/kernel/printk/Makefile index 4d052fc6bcde..eee3dc9b60a9 100644 --- a/kernel/printk/Makefile +++ b/kernel/printk/Makefile @@ -2,3 +2,4 @@ obj-y = printk.o obj-$(CONFIG_PRINTK) += printk_safe.o obj-$(CONFIG_A11Y_BRAILLE_CONSOLE) += braille.o +obj-$(CONFIG_PRINTK) += printk_ringbuffer.o diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c new file mode 100644 index 000000000000..7355ca99e852 --- /dev/null +++ b/kernel/printk/printk_ringbuffer.c @@ -0,0 +1,1687 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include <linux/kernel.h> +#include <linux/irqflags.h> +#include <linux/string.h> +#include <linux/errno.h> +#include <linux/bug.h> +#include "printk_ringbuffer.h" + +/** + * DOC: printk_ringbuffer overview + * + * Data Structure + * -------------- + * The printk_ringbuffer is made up of 3 internal ringbuffers: + * + * desc_ring + * A ring of descriptors. A descriptor contains all record meta data + * (sequence number, timestamp, loglevel, etc.) as well as internal state + * information about the record and logical positions specifying where in + * the other ringbuffers the text and dictionary strings are located. + * + * text_data_ring + * A ring of data blocks. A data block consists of an unsigned long + * integer (ID) that maps to a desc_ring index followed by the text + * string of the record. + * + * dict_data_ring + * A ring of data blocks. A data block consists of an unsigned long + * integer (ID) that maps to a desc_ring index followed by the dictionary + * string of the record. + * + * The internal state information of a descriptor is the key element to allow + * readers and writers to locklessly synchronize access to the data. + * + * Implementation + * -------------- + * + * Descriptor Ring + * ~~~~~~~~~~~~~~~ + * The descriptor ring is an array of descriptors. A descriptor contains all + * the meta data of a printk record as well as blk_lpos structs pointing to + * associated text and dictionary data blocks (see "Data Rings" below). Each + * descriptor is assigned an ID that maps directly to index values of the + * descriptor array and has a state. The ID and the state are bitwise combined + * into a single descriptor field named @state_var, allowing ID and state to + * be synchronously and atomically updated. + * + * Descriptors have three states: + * + * reserved + * A writer is modifying the record. + * + * committed + * The record and all its data are complete and available for reading. + * + * reusable + * The record exists, but its text and/or dictionary data may no longer + * be available. + * + * Querying the @state_var of a record requires providing the ID of the + * descriptor to query. This can yield a possible fourth (pseudo) state: + * + * miss + * The descriptor being queried has an unexpected ID. + * + * The descriptor ring has a @tail_id that contains the ID of the oldest + * descriptor and @head_id that contains the ID of the newest descriptor. + * + * When a new descriptor should be created (and the ring is full), the tail + * descriptor is invalidated by first transitioning to the reusable state and + * then invalidating all tail data blocks up to and including the data blocks + * associated with the tail descriptor (for text and dictionary rings). Then + * @tail_id is advanced, followed by advancing @head_id. And finally the + * @state_var of the new descriptor is initialized to the new ID and reserved + * state. + * + * The @tail_id can only be advanced if the new @tail_id would be in the + * committed or reusable queried state. This makes it possible that a valid + * sequence number of the tail is always available. + * + * Data Rings + * ~~~~~~~~~~ + * The two data rings (text and dictionary) function identically. They exist + * separately so that their buffer sizes can be individually set and they do + * not affect one another. + * + * Data rings are byte arrays composed of data blocks. Data blocks are + * referenced by blk_lpos structs that point to the logical position of the + * beginning of a data block and the beginning of the next adjacent data + * block. Logical positions are mapped directly to index values of the byte + * array ringbuffer. + * + * Each data block consists of an ID followed by the writer data. The ID is + * the identifier of a descriptor that is associated with the data block. A + * given data block is considered valid if all of the following conditions + * are met: + * + * 1) The descriptor associated with the data block is in the committed + * queried state. + * + * 2) The blk_lpos struct within the descriptor associated with the data + * block references back to the same data block. + * + * 3) The data block is within the head/tail logical position range. + * + * If the writer data of a data block would extend beyond the end of the + * byte array, only the ID of the data block is stored at the logical + * position and the full data block (ID and writer data) is stored at the + * beginning of the byte array. The referencing blk_lpos will point to the + * ID before the wrap and the next data block will be at the logical + * position adjacent the full data block after the wrap. + * + * Data rings have a @tail_lpos that points to the beginning of the oldest + * data block and a @head_lpos that points to the logical position of the + * next (not yet existing) data block. + * + * When a new data block should be created (and the ring is full), tail data + * blocks will first be invalidated by putting their associated descriptors + * into the reusable state and then pushing the @tail_lpos forward beyond + * them. Then the @head_lpos is pushed forward and is associated with a new + * descriptor. If a data block is not valid, the @tail_lpos cannot be + * advanced beyond it. + * + * Usage + * ----- + * Here are some simple examples demonstrating writers and readers. For the + * examples a global ringbuffer (test_rb) is available (which is not the + * actual ringbuffer used by printk):: + * + * DEFINE_PRINTKRB(test_rb, 15, 5, 3); + * + * This ringbuffer allows up to 32768 records (2 ^ 15) and has a size of + * 1 MiB (2 ^ (15 + 5)) for text data and 256 KiB (2 ^ (15 + 3)) for + * dictionary data. + * + * Sample writer code:: + * + * const char *dictstr = "dictionary text"; + * const char *textstr = "message text"; + * struct prb_reserved_entry e; + * struct printk_record r; + * + * // specify how much to allocate + * prb_rec_init_wr(&r, strlen(textstr) + 1, strlen(dictstr) + 1); + * + * if (prb_reserve(&e, &test_rb, &r)) { + * snprintf(r.text_buf, r.text_buf_size, "%s", textstr); + * + * // dictionary allocation may have failed + * if (r.dict_buf) + * snprintf(r.dict_buf, r.dict_buf_size, "%s", dictstr); + * + * r.info->ts_nsec = local_clock(); + * + * prb_commit(&e); + * } + * + * Sample reader code:: + * + * struct printk_info info; + * struct printk_record r; + * char text_buf[32]; + * char dict_buf[32]; + * u64 seq; + * + * prb_rec_init_rd(&r, &info, &text_buf[0], sizeof(text_buf), + * &dict_buf[0], sizeof(dict_buf)); + * + * prb_for_each_record(0, &test_rb, &seq, &r) { + * if (info.seq != seq) + * pr_warn("lost %llu records\n", info.seq - seq); + * + * if (info.text_len > r.text_buf_size) { + * pr_warn("record %llu text truncated\n", info.seq); + * text_buf[r.text_buf_size - 1] = 0; + * } + * + * if (info.dict_len > r.dict_buf_size) { + * pr_warn("record %llu dict truncated\n", info.seq); + * dict_buf[r.dict_buf_size - 1] = 0; + * } + * + * pr_info("%llu: %llu: %s;%s\n", info.seq, info.ts_nsec, + * &text_buf[0], info.dict_len ? &dict_buf[0] : ""); + * } + * + * Note that additional less convenient reader functions are available to + * allow complex record access. + * + * ABA Issues + * ~~~~~~~~~~ + * To help avoid ABA issues, descriptors are referenced by IDs (array index + * values combined with tagged bits counting array wraps) and data blocks are + * referenced by logical positions (array index values combined with tagged + * bits counting array wraps). However, on 32-bit systems the number of + * tagged bits is relatively small such that an ABA incident is (at least + * theoretically) possible. For example, if 4 million maximally sized (1KiB) + * printk messages were to occur in NMI context on a 32-bit system, the + * interrupted context would not be able to recognize that the 32-bit integer + * completely wrapped and thus represents a different data block than the one + * the interrupted context expects. + * + * To help combat this possibility, additional state checking is performed + * (such as using cmpxchg() even though set() would suffice). These extra + * checks are commented as such and will hopefully catch any ABA issue that + * a 32-bit system might experience. + * + * Memory Barriers + * ~~~~~~~~~~~~~~~ + * Multiple memory barriers are used. To simplify proving correctness and + * generating litmus tests, lines of code related to memory barriers + * (loads, stores, and the associated memory barriers) are labeled:: + * + * LMM(function:letter) + * + * Comments reference the labels using only the "function:letter" part. + * + * The memory barrier pairs and their ordering are: + * + * desc_reserve:D / desc_reserve:B + * push descriptor tail (id), then push descriptor head (id) + * + * desc_reserve:D / data_push_tail:B + * push data tail (lpos), then set new descriptor reserved (state) + * + * desc_reserve:D / desc_push_tail:C + * push descriptor tail (id), then set new descriptor reserved (state) + * + * desc_reserve:D / prb_first_seq:C + * push descriptor tail (id), then set new descriptor reserved (state) + * + * desc_reserve:F / desc_read:D + * set new descriptor id and reserved (state), then allow writer changes + * + * data_alloc:A / desc_read:D + * set old descriptor reusable (state), then modify new data block area + * + * data_alloc:A / data_push_tail:B + * push data tail (lpos), then modify new data block area + * + * prb_commit:B / desc_read:B + * store writer changes, then set new descriptor committed (state) + * + * data_push_tail:D / data_push_tail:A + * set descriptor reusable (state), then push data tail (lpos) + * + * desc_push_tail:B / desc_reserve:D + * set descriptor reusable (state), then push descriptor tail (id) + */ + +#define DATA_SIZE(data_ring) _DATA_SIZE((data_ring)->size_bits) +#define DATA_SIZE_MASK(data_ring) (DATA_SIZE(data_ring) - 1) + +#define DESCS_COUNT(desc_ring) _DESCS_COUNT((desc_ring)->count_bits) +#define DESCS_COUNT_MASK(desc_ring) (DESCS_COUNT(desc_ring) - 1) + +/* Determine the data array index from a logical position. */ +#define DATA_INDEX(data_ring, lpos) ((lpos) & DATA_SIZE_MASK(data_ring)) + +/* Determine the desc array index from an ID or sequence number. */ +#define DESC_INDEX(desc_ring, n) ((n) & DESCS_COUNT_MASK(desc_ring)) + +/* Determine how many times the data array has wrapped. */ +#define DATA_WRAPS(data_ring, lpos) ((lpos) >> (data_ring)->size_bits) + +/* Get the logical position at index 0 of the current wrap. */ +#define DATA_THIS_WRAP_START_LPOS(data_ring, lpos) \ +((lpos) & ~DATA_SIZE_MASK(data_ring)) + +/* Get the ID for the same index of the previous wrap as the given ID. */ +#define DESC_ID_PREV_WRAP(desc_ring, id) \ +DESC_ID((id) - DESCS_COUNT(desc_ring)) + +/* + * A data block: mapped directly to the beginning of the data block area + * specified as a logical position within the data ring. + * + * @id: the ID of the associated descriptor + * @data: the writer data + * + * Note that the size of a data block is only known by its associated + * descriptor. + */ +struct prb_data_block { + unsigned long id; + char data[0]; +}; + +/* + * Return the descriptor associated with @n. @n can be either a + * descriptor ID or a sequence number. + */ +static struct prb_desc *to_desc(struct prb_desc_ring *desc_ring, u64 n) +{ + return &desc_ring->descs[DESC_INDEX(desc_ring, n)]; +} + +static struct prb_data_block *to_block(struct prb_data_ring *data_ring, + unsigned long begin_lpos) +{ + return (void *)&data_ring->data[DATA_INDEX(data_ring, begin_lpos)]; +} + +/* + * Increase the data size to account for data block meta data plus any + * padding so that the adjacent data block is aligned on the ID size. + */ +static unsigned int to_blk_size(unsigned int size) +{ + struct prb_data_block *db = NULL; + + size += sizeof(*db); + size = ALIGN(size, sizeof(db->id)); + return size; +} + +/* + * Sanity checker for reserve size. The ringbuffer code assumes that a data + * block does not exceed the maximum possible size that could fit within the + * ringbuffer. This function provides that basic size check so that the + * assumption is safe. + * + * Writers are also not allowed to write 0-sized (data-less) records. Such + * records are used only internally by the ringbuffer. + */ +static bool data_check_size(struct prb_data_ring *data_ring, unsigned int size) +{ + struct prb_data_block *db = NULL; + + /* + * Writers are not allowed to write data-less records. Such records + * are used only internally by the ringbuffer to denote records where + * their data failed to allocate or have been lost. + */ + if (size == 0) + return false; + + /* + * Ensure the alignment padded size could possibly fit in the data + * array. The largest possible data block must still leave room for + * at least the ID of the next block. + */ + size = to_blk_size(size); + if (size > DATA_SIZE(data_ring) - sizeof(db->id)) + return false; + + return true; +} + +/* The possible responses of a descriptor state-query. */ +enum desc_state { + desc_miss, /* ID mismatch */ + desc_reserved, /* reserved, in use by writer */ + desc_committed, /* committed, writer is done */ + desc_reusable, /* free, not yet used by any writer */ +}; + +/* Query the state of a descriptor. */ +static enum desc_state get_desc_state(unsigned long id, + unsigned long state_val) +{ + if (id != DESC_ID(state_val)) + return desc_miss; + + if (state_val & DESC_REUSE_MASK) + return desc_reusable; + + if (state_val & DESC_COMMITTED_MASK) + return desc_committed; + + return desc_reserved; +} + +/* + * Get a copy of a specified descriptor and its queried state. A descriptor + * that is not in the committed or reusable state must be considered garbage + * by the reader. + */ +static enum desc_state desc_read(struct prb_desc_ring *desc_ring, + unsigned long id, struct prb_desc *desc_out) +{ + struct prb_desc *desc = to_desc(desc_ring, id); + atomic_long_t *state_var = &desc->state_var; + enum desc_state d_state; + unsigned long state_val; + + /* Check the descriptor state. */ + state_val = atomic_long_read(state_var); /* LMM(desc_read:A) */ + d_state = get_desc_state(id, state_val); + if (d_state != desc_committed && d_state != desc_reusable) + return d_state; + + /* + * Guarantee the state is loaded before copying the descriptor + * content. This avoids copying obsolete descriptor content that might + * not apply to the descriptor state. This pairs with prb_commit:B. + * + * Memory barrier involvement: + * + * If desc_read:A reads from prb_commit:B, then desc_read:C reads + * from prb_commit:A. + * + * Relies on: + * + * WMB from prb_commit:A to prb_commit:B + * matching + * RMB from desc_read:A to desc_read:C + */ + smp_rmb(); /* LMM(desc_read:B) */ + + /* + * Copy the descriptor data. The data is not valid until the + * state has been re-checked. + */ + memcpy(desc_out, desc, sizeof(*desc_out)); /* LMM(desc_read:C) */ + + /* + * 1. Guarantee the descriptor content is loaded before re-checking + * the state. This avoids reading an obsolete descriptor state + * that may not apply to the copied content. This pairs with + * desc_reserve:F. + * + * Memory barrier involvement: + * + * If desc_read:C reads from desc_reserve:G, then desc_read:E + * reads from desc_reserve:F. + * + * Relies on: + * + * WMB from desc_reserve:F to desc_reserve:G + * matching + * RMB from desc_read:C to desc_read:E + * + * 2. Guarantee the record data is loaded before re-checking the + * state. This avoids reading an obsolete descriptor state that may + * not apply to the copied data. This pairs with data_alloc:A. + * + * Memory barrier involvement: + * + * If copy_data:A reads from data_alloc:B, then desc_read:E + * reads from desc_make_reusable:A. + * + * Relies on: + * + * MB from desc_make_reusable:A to data_alloc:B + * matching + * RMB from desc_read:C to desc_read:E + * + * Note: desc_make_reusable:A and data_alloc:B can be different + * CPUs. However, the data_alloc:B CPU (which performs the + * full memory barrier) must have previously seen + * desc_make_reusable:A. + */ + smp_rmb(); /* LMM(desc_read:D) */ + + /* Re-check the descriptor state. */ + state_val = atomic_long_read(state_var); /* LMM(desc_read:E) */ + return get_desc_state(id, state_val); +} + +/* + * Take a specified descriptor out of the committed state by attempting + * the transition from committed to reusable. Either this context or some + * other context will have been successful. + */ +static void desc_make_reusable(struct prb_desc_ring *desc_ring, + unsigned long id) +{ + unsigned long val_committed = id | DESC_COMMITTED_MASK; + unsigned long val_reusable = val_committed | DESC_REUSE_MASK; + struct prb_desc *desc = to_desc(desc_ring, id); + atomic_long_t *state_var = &desc->state_var; + + atomic_long_cmpxchg_relaxed(state_var, val_committed, + val_reusable); /* LMM(desc_make_reusable:A) */ +} + +/* + * Given a data ring (text or dict), put the associated descriptor of each + * data block from @lpos_begin until @lpos_end into the reusable state. + * + * If there is any problem making the associated descriptor reusable, either + * the descriptor has not yet been committed or another writer context has + * already pushed the tail lpos past the problematic data block. Regardless, + * on error the caller can re-load the tail lpos to determine the situation. + */ +static bool data_make_reusable(struct printk_ringbuffer *rb, + struct prb_data_ring *data_ring, + unsigned long lpos_begin, + unsigned long lpos_end, + unsigned long *lpos_out) +{ + struct prb_desc_ring *desc_ring = &rb->desc_ring; + struct prb_data_blk_lpos *blk_lpos; + struct prb_data_block *blk; + enum desc_state d_state; + struct prb_desc desc; + unsigned long id; + + /* + * Using the provided @data_ring, point @blk_lpos to the correct + * blk_lpos within the local copy of the descriptor. + */ + if (data_ring == &rb->text_data_ring) + blk_lpos = &desc.text_blk_lpos; + else + blk_lpos = &desc.dict_blk_lpos; + + /* Loop until @lpos_begin has advanced to or beyond @lpos_end. */ + while ((lpos_end - lpos_begin) - 1 < DATA_SIZE(data_ring)) { + blk = to_block(data_ring, lpos_begin); + + /* + * Load the block ID from the data block. This is a data race + * against a writer that may have newly reserved this data + * area. If the loaded value matches a valid descriptor ID, + * the blk_lpos of that descriptor will be checked to make + * sure it points back to this data block. If the check fails, + * the data area has been recycled by another writer. + */ + id = blk->id; /* LMM(data_make_reusable:A) */ + + d_state = desc_read(desc_ring, id, &desc); /* LMM(data_make_reusable:B) */ + + switch (d_state) { + case desc_miss: + return false; + case desc_reserved: + return false; + case desc_committed: + /* + * This data block is invalid if the descriptor + * does not point back to it. + */ + if (blk_lpos->begin != lpos_begin) + return false; + desc_make_reusable(desc_ring, id); + break; + case desc_reusable: + /* + * This data block is invalid if the descriptor + * does not point back to it. + */ + if (blk_lpos->begin != lpos_begin) + return false; + break; + } + + /* Advance @lpos_begin to the next data block. */ + lpos_begin = blk_lpos->next; + } + + *lpos_out = lpos_begin; + return true; +} + +/* + * Advance the data ring tail to at least @lpos. This function puts + * descriptors into the reusable state if the tail is pushed beyond + * their associated data block. + */ +static bool data_push_tail(struct printk_ringbuffer *rb, + struct prb_data_ring *data_ring, + unsigned long lpos) +{ + unsigned long tail_lpos_new; + unsigned long tail_lpos; + unsigned long next_lpos; + + /* If @lpos is not valid, there is nothing to do. */ + if (lpos == INVALID_LPOS) + return true; + + /* + * Any descriptor states that have transitioned to reusable due to the + * data tail being pushed to this loaded value will be visible to this + * CPU. This pairs with data_push_tail:D. + * + * Memory barrier involvement: + * + * If data_push_tail:A reads from data_push_tail:D, then this CPU can + * see desc_make_reusable:A. + * + * Relies on: + * + * MB from desc_make_reusable:A to data_push_tail:D + * matches + * READFROM from data_push_tail:D to data_push_tail:A + * thus + * READFROM from desc_make_reusable:A to this CPU + */ + tail_lpos = atomic_long_read(&data_ring->tail_lpos); /* LMM(data_push_tail:A) */ + + /* + * Loop until the tail lpos is at or beyond @lpos. This condition + * may already be satisfied, resulting in no full memory barrier + * from data_push_tail:D being performed. However, since this CPU + * sees the new tail lpos, any descriptor states that transitioned to + * the reusable state must already be visible. + */ + while ((lpos - tail_lpos) - 1 < DATA_SIZE(data_ring)) { + /* + * Make all descriptors reusable that are associated with + * data blocks before @lpos. + */ + if (!data_make_reusable(rb, data_ring, tail_lpos, lpos, + &next_lpos)) { + /* + * 1. Guarantee the block ID loaded in + * data_make_reusable() is performed before + * reloading the tail lpos. The failed + * data_make_reusable() may be due to a newly + * recycled data area causing the tail lpos to + * have been previously pushed. This pairs with + * data_alloc:A. + * + * Memory barrier involvement: + * + * If data_make_reusable:A reads from data_alloc:B, + * then data_push_tail:C reads from + * data_push_tail:D. + * + * Relies on: + * + * MB from data_push_tail:D to data_alloc:B + * matching + * RMB from data_make_reusable:A to + * data_push_tail:C + * + * Note: data_push_tail:D and data_alloc:B can be + * different CPUs. However, the data_alloc:B + * CPU (which performs the full memory + * barrier) must have previously seen + * data_push_tail:D. + * + * 2. Guarantee the descriptor state loaded in + * data_make_reusable() is performed before + * reloading the tail lpos. The failed + * data_make_reusable() may be due to a newly + * recycled descriptor causing the tail lpos to + * have been previously pushed. This pairs with + * desc_reserve:D. + * + * Memory barrier involvement: + * + * If data_make_reusable:B reads from + * desc_reserve:F, then data_push_tail:C reads + * from data_push_tail:D. + * + * Relies on: + * + * MB from data_push_tail:D to desc_reserve:F + * matching + * RMB from data_make_reusable:B to + * data_push_tail:C + * + * Note: data_push_tail:D and desc_reserve:F can + * be different CPUs. However, the + * desc_reserve:F CPU (which performs the + * full memory barrier) must have previously + * seen data_push_tail:D. + */ + smp_rmb(); /* LMM(data_push_tail:B) */ + + tail_lpos_new = atomic_long_read(&data_ring->tail_lpos + ); /* LMM(data_push_tail:C) */ + if (tail_lpos_new == tail_lpos) + return false; + + /* Another CPU pushed the tail. Try again. */ + tail_lpos = tail_lpos_new; + continue; + } + + /* + * Guarantee any descriptor states that have transitioned to + * reusable are stored before pushing the tail lpos. A full + * memory barrier is needed since other CPUs may have made + * the descriptor states reusable. This pairs with + * data_push_tail:A. + */ + if (atomic_long_try_cmpxchg(&data_ring->tail_lpos, &tail_lpos, + next_lpos)) { /* LMM(data_push_tail:D) */ + break; + } + } + + return true; +} + +/* + * Advance the desc ring tail. This function advances the tail by one + * descriptor, thus invalidating the oldest descriptor. Before advancing + * the tail, the tail descriptor is made reusable and all data blocks up to + * and including the descriptor's data block are invalidated (i.e. the data + * ring tail is pushed past the data block of the descriptor being made + * reusable). + */ +static bool desc_push_tail(struct printk_ringbuffer *rb, + unsigned long tail_id) +{ + struct prb_desc_ring *desc_ring = &rb->desc_ring; + enum desc_state d_state; + struct prb_desc desc; + + d_state = desc_read(desc_ring, tail_id, &desc); + + switch (d_state) { + case desc_miss: + /* + * If the ID is exactly 1 wrap behind the expected, it is + * in the process of being reserved by another writer and + * must be considered reserved. + */ + if (DESC_ID(atomic_long_read(&desc.state_var)) == + DESC_ID_PREV_WRAP(desc_ring, tail_id)) { + return false; + } + + /* + * The ID has changed. Another writer must have pushed the + * tail and recycled the descriptor already. Success is + * returned because the caller is only interested in the + * specified tail being pushed, which it was. + */ + return true; + case desc_reserved: + return false; + case desc_committed: + desc_make_reusable(desc_ring, tail_id); + break; + case desc_reusable: + break; + } + + /* + * Data blocks must be invalidated before their associated + * descriptor can be made available for recycling. Invalidating + * them later is not possible because there is no way to trust + * data blocks once their associated descriptor is gone. + */ + + if (!data_push_tail(rb, &rb->text_data_ring, desc.text_blk_lpos.next)) + return false; + if (!data_push_tail(rb, &rb->dict_data_ring, desc.dict_blk_lpos.next)) + return false; + + /* + * Check the next descriptor after @tail_id before pushing the tail + * to it because the tail must always be in a committed or reusable + * state. The implementation of prb_first_seq() relies on this. + * + * A successful read implies that the next descriptor is less than or + * equal to @head_id so there is no risk of pushing the tail past the + * head. + */ + d_state = desc_read(desc_ring, DESC_ID(tail_id + 1), &desc); /* LMM(desc_push_tail:A) */ + + if (d_state == desc_committed || d_state == desc_reusable) { + /* + * Guarantee any descriptor states that have transitioned to + * reusable are stored before pushing the tail ID. This allows + * verifying the recycled descriptor state. A full memory + * barrier is needed since other CPUs may have made the + * descriptor states reusable. This pairs with desc_reserve:D. + */ + atomic_long_cmpxchg(&desc_ring->tail_id, tail_id, + DESC_ID(tail_id + 1)); /* LMM(desc_push_tail:B) */ + } else { + /* + * Guarantee the last state load from desc_read() is before + * reloading @tail_id in order to see a new tail ID in the + * case that the descriptor has been recycled. This pairs + * with desc_reserve:D. + * + * Memory barrier involvement: + * + * If desc_push_tail:A reads from desc_reserve:F, then + * desc_push_tail:D reads from desc_push_tail:B. + * + * Relies on: + * + * MB from desc_push_tail:B to desc_reserve:F + * matching + * RMB from desc_push_tail:A to desc_push_tail:D + * + * Note: desc_push_tail:B and desc_reserve:F can be different + * CPUs. However, the desc_reserve:F CPU (which performs + * the full memory barrier) must have previously seen + * desc_push_tail:B. + */ + smp_rmb(); /* LMM(desc_push_tail:C) */ + + /* + * Re-check the tail ID. The descriptor following @tail_id is + * not in an allowed tail state. But if the tail has since + * been moved by another CPU, then it does not matter. + */ + if (atomic_long_read(&desc_ring->tail_id) == tail_id) /* LMM(desc_push_tail:D) */ + return false; + } + + return true; +} + +/* Reserve a new descriptor, invalidating the oldest if necessary. */ +static bool desc_reserve(struct printk_ringbuffer *rb, unsigned long *id_out) +{ + struct prb_desc_ring *desc_ring = &rb->desc_ring; + unsigned long prev_state_val; + unsigned long id_prev_wrap; + struct prb_desc *desc; + unsigned long head_id; + unsigned long id; + + head_id = atomic_long_read(&desc_ring->head_id); /* LMM(desc_reserve:A) */ + + do { + desc = to_desc(desc_ring, head_id); + + id = DESC_ID(head_id + 1); + id_prev_wrap = DESC_ID_PREV_WRAP(desc_ring, id); + + /* + * Guarantee the head ID is read before reading the tail ID. + * Since the tail ID is updated before the head ID, this + * guarantees that @id_prev_wrap is never ahead of the tail + * ID. This pairs with desc_reserve:D. + * + * Memory barrier involvement: + * + * If desc_reserve:A reads from desc_reserve:D, then + * desc_reserve:C reads from desc_push_tail:B. + * + * Relies on: + * + * MB from desc_push_tail:B to desc_reserve:D + * matching + * RMB from desc_reserve:A to desc_reserve:C + * + * Note: desc_push_tail:B and desc_reserve:D can be different + * CPUs. However, the desc_reserve:D CPU (which performs + * the full memory barrier) must have previously seen + * desc_push_tail:B. + */ + smp_rmb(); /* LMM(desc_reserve:B) */ + + if (id_prev_wrap == atomic_long_read(&desc_ring->tail_id + )) { /* LMM(desc_reserve:C) */ + /* + * Make space for the new descriptor by + * advancing the tail. + */ + if (!desc_push_tail(rb, id_prev_wrap)) + return false; + } + + /* + * 1. Guarantee the tail ID is read before validating the + * recycled descriptor state. A read memory barrier is + * sufficient for this. This pairs with desc_push_tail:B. + * + * Memory barrier involvement: + * + * If desc_reserve:C reads from desc_push_tail:B, then + * desc_reserve:E reads from desc_make_reusable:A. + * + * Relies on: + * + * MB from desc_make_reusable:A to desc_push_tail:B + * matching + * RMB from desc_reserve:C to desc_reserve:E + * + * Note: desc_make_reusable:A and desc_push_tail:B can be + * different CPUs. However, the desc_push_tail:B CPU + * (which performs the full memory barrier) must have + * previously seen desc_make_reusable:A. + * + * 2. Guarantee the tail ID is stored before storing the head + * ID. This pairs with desc_reserve:B. + * + * 3. Guarantee any data ring tail changes are stored before + * recycling the descriptor. Data ring tail changes can + * happen via desc_push_tail()->data_push_tail(). A full + * memory barrier is needed since another CPU may have + * pushed the data ring tails. This pairs with + * data_push_tail:B. + * + * 4. Guarantee a new tail ID is stored before recycling the + * descriptor. A full memory barrier is needed since + * another CPU may have pushed the tail ID. This pairs + * with desc_push_tail:C and this also pairs with + * prb_first_seq:C. + */ + } while (!atomic_long_try_cmpxchg(&desc_ring->head_id, &head_id, + id)); /* LMM(desc_reserve:D) */ + + desc = to_desc(desc_ring, id); + + /* + * If the descriptor has been recycled, verify the old state val. + * See "ABA Issues" about why this verification is performed. + */ + prev_state_val = atomic_long_read(&desc->state_var); /* LMM(desc_reserve:E) */ + if (prev_state_val && + prev_state_val != (id_prev_wrap | DESC_COMMITTED_MASK | DESC_REUSE_MASK)) { + WARN_ON_ONCE(1); + return false; + } + + /* + * Assign the descriptor a new ID and set its state to reserved. + * See "ABA Issues" about why cmpxchg() instead of set() is used. + * + * Guarantee the new descriptor ID and state is stored before making + * any other changes. A write memory barrier is sufficient for this. + * This pairs with desc_read:D. + */ + if (!atomic_long_try_cmpxchg(&desc->state_var, &prev_state_val, + id | 0)) { /* LMM(desc_reserve:F) */ + WARN_ON_ONCE(1); + return false; + } + + /* Now data in @desc can be modified: LMM(desc_reserve:G) */ + + *id_out = id; + return true; +} + +/* Determine the end of a data block. */ +static unsigned long get_next_lpos(struct prb_data_ring *data_ring, + unsigned long lpos, unsigned int size) +{ + unsigned long begin_lpos; + unsigned long next_lpos; + + begin_lpos = lpos; + next_lpos = lpos + size; + + /* First check if the data block does not wrap. */ + if (DATA_WRAPS(data_ring, begin_lpos) == DATA_WRAPS(data_ring, next_lpos)) + return next_lpos; + + /* Wrapping data blocks store their data at the beginning. */ + return (DATA_THIS_WRAP_START_LPOS(data_ring, next_lpos) + size); +} + +/* + * Allocate a new data block, invalidating the oldest data block(s) + * if necessary. This function also associates the data block with + * a specified descriptor. + */ +static char *data_alloc(struct printk_ringbuffer *rb, + struct prb_data_ring *data_ring, unsigned int size, + struct prb_data_blk_lpos *blk_lpos, unsigned long id) +{ + struct prb_data_block *blk; + unsigned long begin_lpos; + unsigned long next_lpos; + + if (size == 0) { + /* Specify a data-less block. */ + blk_lpos->begin = INVALID_LPOS; + blk_lpos->next = INVALID_LPOS; + return NULL; + } + + size = to_blk_size(size); + + begin_lpos = atomic_long_read(&data_ring->head_lpos); + + do { + next_lpos = get_next_lpos(data_ring, begin_lpos, size); + + if (!data_push_tail(rb, data_ring, next_lpos - DATA_SIZE(data_ring))) { + /* Failed to allocate, specify a data-less block. */ + blk_lpos->begin = INVALID_LPOS; + blk_lpos->next = INVALID_LPOS; + return NULL; + } + + /* + * 1. Guarantee any descriptor states that have transitioned + * to reusable are stored before modifying the newly + * allocated data area. A full memory barrier is needed + * since other CPUs may have made the descriptor states + * reusable. See data_push_tail:A about why the reusable + * states are visible. This pairs with desc_read:D. + * + * 2. Guarantee any updated tail lpos is stored before + * modifying the newly allocated data area. Another CPU may + * be in data_make_reusable() and is reading a block ID + * from this area. data_make_reusable() can handle reading + * a garbage block ID value, but then it must be able to + * load a new tail lpos. A full memory barrier is needed + * since other CPUs may have updated the tail lpos. This + * pairs with data_push_tail:B. + */ + } while (!atomic_long_try_cmpxchg(&data_ring->head_lpos, &begin_lpos, + next_lpos)); /* LMM(data_alloc:A) */ + + blk = to_block(data_ring, begin_lpos); + blk->id = id; /* LMM(data_alloc:B) */ + + if (DATA_WRAPS(data_ring, begin_lpos) != DATA_WRAPS(data_ring, next_lpos)) { + /* Wrapping data blocks store their data at the beginning. */ + blk = to_block(data_ring, 0); + + /* + * Store the ID on the wrapped block for consistency. + * The printk_ringbuffer does not actually use it. + */ + blk->id = id; + } + + blk_lpos->begin = begin_lpos; + blk_lpos->next = next_lpos; + + return &blk->data[0]; +} + +/* Return the number of bytes used by a data block. */ +static unsigned int space_used(struct prb_data_ring *data_ring, + struct prb_data_blk_lpos *blk_lpos) +{ + if (DATA_WRAPS(data_ring, blk_lpos->begin) == DATA_WRAPS(data_ring, blk_lpos->next)) { + /* Data block does not wrap. */ + return (DATA_INDEX(data_ring, blk_lpos->next) - + DATA_INDEX(data_ring, blk_lpos->begin)); + } + + /* + * For wrapping data blocks, the trailing (wasted) space is + * also counted. + */ + return (DATA_INDEX(data_ring, blk_lpos->next) + + DATA_SIZE(data_ring) - DATA_INDEX(data_ring, blk_lpos->begin)); +} + +/** + * prb_reserve() - Reserve space in the ringbuffer. + * + * @e: The entry structure to setup. + * @rb: The ringbuffer to reserve data in. + * @r: The record structure to allocate buffers for. + * + * This is the public function available to writers to reserve data. + * + * The writer specifies the text and dict sizes to reserve by setting the + * @text_buf_size and @dict_buf_size fields of @r, respectively. Dictionaries + * are optional, so @dict_buf_size is allowed to be 0. To ensure proper + * initialization of @r, prb_rec_init_wr() should be used. + * + * Context: Any context. Disables local interrupts on success. + * Return: true if at least text data could be allocated, otherwise false. + * + * On success, the fields @info, @text_buf, @dict_buf of @r will be set by + * this function and should be filled in by the writer before committing. Also + * on success, prb_record_text_space() can be used on @e to query the actual + * space used for the text data block. + * + * If the function fails to reserve dictionary space (but all else succeeded), + * it will still report success. In that case @dict_buf is set to NULL and + * @dict_buf_size is set to 0. Writers must check this before writing to + * dictionary space. + * + * @info->text_len and @info->dict_len will already be set to @text_buf_size + * and @dict_buf_size, respectively. If dictionary space reservation fails, + * @info->dict_len is set to 0. + */ +bool prb_reserve(struct prb_reserved_entry *e, struct printk_ringbuffer *rb, + struct printk_record *r) +{ + struct prb_desc_ring *desc_ring = &rb->desc_ring; + struct prb_desc *d; + unsigned long id; + + if (!data_check_size(&rb->text_data_ring, r->text_buf_size)) + goto fail; + + /* Records are allowed to not have dictionaries. */ + if (r->dict_buf_size) { + if (!data_check_size(&rb->dict_data_ring, r->dict_buf_size)) + goto fail; + } + + /* + * Descriptors in the reserved state act as blockers to all further + * reservations once the desc_ring has fully wrapped. Disable + * interrupts during the reserve/commit window in order to minimize + * the likelihood of this happening. + */ + local_irq_save(e->irqflags); + + if (!desc_reserve(rb, &id)) { + /* Descriptor reservation failures are tracked. */ + atomic_long_inc(&rb->fail); + local_irq_restore(e->irqflags); + goto fail; + } + + d = to_desc(desc_ring, id); + + /* + * Set the @e fields here so that prb_commit() can be used if + * text data allocation fails. + */ + e->rb = rb; + e->id = id; + + /* + * Initialize the sequence number if it has "never been set". + * Otherwise just increment it by a full wrap. + * + * @seq is considered "never been set" if it has a value of 0, + * _except_ for @descs[0], which was specially setup by the ringbuffer + * initializer and therefore is always considered as set. + * + * See the "Bootstrap" comment block in printk_ringbuffer.h for + * details about how the initializer bootstraps the descriptors. + */ + if (d->info.seq == 0 && DESC_INDEX(desc_ring, id) != 0) + d->info.seq = DESC_INDEX(desc_ring, id); + else + d->info.seq += DESCS_COUNT(desc_ring); + + r->text_buf = data_alloc(rb, &rb->text_data_ring, r->text_buf_size, + &d->text_blk_lpos, id); + /* If text data allocation fails, a data-less record is committed. */ + if (r->text_buf_size && !r->text_buf) { + d->info.text_len = 0; + d->info.dict_len = 0; + prb_commit(e); + /* prb_commit() re-enabled interrupts. */ + goto fail; + } + + r->dict_buf = data_alloc(rb, &rb->dict_data_ring, r->dict_buf_size, + &d->dict_blk_lpos, id); + /* + * If dict data allocation fails, the caller can still commit + * text. But dictionary information will not be available. + */ + if (r->dict_buf_size && !r->dict_buf) + r->dict_buf_size = 0; + + r->info = &d->info; + + /* Set default values for the sizes. */ + d->info.text_len = r->text_buf_size; + d->info.dict_len = r->dict_buf_size; + + /* Record full text space used by record. */ + e->text_space = space_used(&rb->text_data_ring, &d->text_blk_lpos); + + return true; +fail: + /* Make it clear to the caller that the reserve failed. */ + memset(r, 0, sizeof(*r)); + return false; +} + +/** + * prb_commit() - Commit (previously reserved) data to the ringbuffer. + * + * @e: The entry containing the reserved data information. + * + * This is the public function available to writers to commit data. + * + * Context: Any context. Enables local interrupts. + */ +void prb_commit(struct prb_reserved_entry *e) +{ + struct prb_desc_ring *desc_ring = &e->rb->desc_ring; + struct prb_desc *d = to_desc(desc_ring, e->id); + unsigned long prev_state_val = e->id | 0; + + /* Now the writer has finished all writing: LMM(prb_commit:A) */ + + /* + * Set the descriptor as committed. See "ABA Issues" about why + * cmpxchg() instead of set() is used. + * + * Guarantee all record data is stored before the descriptor state + * is stored as committed. A write memory barrier is sufficient for + * this. This pairs with desc_read:B. + */ + if (!atomic_long_try_cmpxchg(&d->state_var, &prev_state_val, + e->id | DESC_COMMITTED_MASK)) { /* LMM(prb_commit:B) */ + WARN_ON_ONCE(1); + } + + /* Restore interrupts, the reserve/commit window is finished. */ + local_irq_restore(e->irqflags); +} + +/* + * Given @blk_lpos, return a pointer to the writer data from the data block + * and calculate the size of the data part. A NULL pointer is returned if + * @blk_lpos specifies values that could never be legal. + * + * This function (used by readers) performs strict validation on the lpos + * values to possibly detect bugs in the writer code. A WARN_ON_ONCE() is + * triggered if an internal error is detected. + */ +static char *get_data(struct prb_data_ring *data_ring, + struct prb_data_blk_lpos *blk_lpos, + unsigned int *data_size) +{ + struct prb_data_block *db; + + /* Data-less data block description. */ + if (blk_lpos->begin == INVALID_LPOS && + blk_lpos->next == INVALID_LPOS) { + return NULL; + } + + /* Regular data block: @begin less than @next and in same wrap. */ + if (DATA_WRAPS(data_ring, blk_lpos->begin) == DATA_WRAPS(data_ring, blk_lpos->next) && + blk_lpos->begin < blk_lpos->next) { + db = to_block(data_ring, blk_lpos->begin); + *data_size = blk_lpos->next - blk_lpos->begin; + + /* Wrapping data block: @begin is one wrap behind @next. */ + } else if (DATA_WRAPS(data_ring, blk_lpos->begin + DATA_SIZE(data_ring)) == + DATA_WRAPS(data_ring, blk_lpos->next)) { + db = to_block(data_ring, 0); + *data_size = DATA_INDEX(data_ring, blk_lpos->next); + + /* Illegal block description. */ + } else { + WARN_ON_ONCE(1); + return NULL; + } + + /* A valid data block will always be aligned to the ID size. */ + if (WARN_ON_ONCE(blk_lpos->begin != ALIGN(blk_lpos->begin, sizeof(db->id))) || + WARN_ON_ONCE(blk_lpos->next != ALIGN(blk_lpos->next, sizeof(db->id)))) { + return NULL; + } + + /* A valid data block will always have at least an ID. */ + if (WARN_ON_ONCE(*data_size < sizeof(db->id))) + return NULL; + + /* Subtract block ID space from size to reflect data size. */ + *data_size -= sizeof(db->id); + + return &db->data[0]; +} + +/* + * Count the number of lines in provided text. All text has at least 1 line + * (even if @text_size is 0). Each '\n' processed is counted as an additional + * line. + */ +static unsigned int count_lines(char *text, unsigned int text_size) +{ + unsigned int next_size = text_size; + unsigned int line_count = 1; + char *next = text; + + while (next_size) { + next = memchr(next, '\n', next_size); + if (!next) + break; + line_count++; + next++; + next_size = text_size - (next - text); + } + + return line_count; +} + +/* + * Given @blk_lpos, copy an expected @len of data into the provided buffer. + * If @line_count is provided, count the number of lines in the data. + * + * This function (used by readers) performs strict validation on the data + * size to possibly detect bugs in the writer code. A WARN_ON_ONCE() is + * triggered if an internal error is detected. + */ +static bool copy_data(struct prb_data_ring *data_ring, + struct prb_data_blk_lpos *blk_lpos, u16 len, char *buf, + unsigned int buf_size, unsigned int *line_count) +{ + unsigned int data_size; + char *data; + + /* Caller might not want any data. */ + if ((!buf || !buf_size) && !line_count) + return true; + + data = get_data(data_ring, blk_lpos, &data_size); + if (!data) + return false; + + /* + * Actual cannot be less than expected. It can be more than expected + * because of the trailing alignment padding. + */ + if (WARN_ON_ONCE(data_size < (unsigned int)len)) { + pr_warn_once("wrong data size (%u, expecting %hu) for data: %.*s\n", + data_size, len, data_size, data); + return false; + } + + /* Caller interested in the line count? */ + if (line_count) + *line_count = count_lines(data, data_size); + + /* Caller interested in the data content? */ + if (!buf || !buf_size) + return true; + + data_size = min_t(u16, buf_size, len); + + if (!WARN_ON_ONCE(!data_size)) + memcpy(&buf[0], data, data_size); /* LMM(copy_data:A) */ + return true; +} + +/* + * This is an extended version of desc_read(). It gets a copy of a specified + * descriptor. However, it also verifies that the record is committed and has + * the sequence number @seq. On success, 0 is returned. + * + * Error return values: + * -EINVAL: A committed record with sequence number @seq does not exist. + * -ENOENT: A committed record with sequence number @seq exists, but its data + * is not available. This is a valid record, so readers should + * continue with the next record. + */ +static int desc_read_committed_seq(struct prb_desc_ring *desc_ring, + unsigned long id, u64 seq, + struct prb_desc *desc_out) +{ + struct prb_data_blk_lpos *blk_lpos = &desc_out->text_blk_lpos; + enum desc_state d_state; + + d_state = desc_read(desc_ring, id, desc_out); + + /* + * An unexpected @id (desc_miss) or @seq mismatch means the record + * does not exist. A descriptor in the reserved state means the + * record does not yet exist for the reader. + */ + if (d_state == desc_miss || + d_state == desc_reserved || + desc_out->info.seq != seq) { + return -EINVAL; + } + + /* + * A descriptor in the reusable state may no longer have its data + * available; report it as a data-less record. Or the record may + * actually be a data-less record. + */ + if (d_state == desc_reusable || + (blk_lpos->begin == INVALID_LPOS && blk_lpos->next == INVALID_LPOS)) { + return -ENOENT; + } + + return 0; +} + +/* + * Copy the ringbuffer data from the record with @seq to the provided + * @r buffer. On success, 0 is returned. + * + * See desc_read_committed_seq() for error return values. + */ +static int prb_read(struct printk_ringbuffer *rb, u64 seq, + struct printk_record *r, unsigned int *line_count) +{ + struct prb_desc_ring *desc_ring = &rb->desc_ring; + struct prb_desc *rdesc = to_desc(desc_ring, seq); + atomic_long_t *state_var = &rdesc->state_var; + struct prb_desc desc; + unsigned long id; + int err; + + /* Extract the ID, used to specify the descriptor to read. */ + id = DESC_ID(atomic_long_read(state_var)); + + /* Get a local copy of the correct descriptor (if available). */ + err = desc_read_committed_seq(desc_ring, id, seq, &desc); + + /* + * If @r is NULL, the caller is only interested in the availability + * of the record. + */ + if (err || !r) + return err; + + /* If requested, copy meta data. */ + if (r->info) + memcpy(r->info, &desc.info, sizeof(*(r->info))); + + /* Copy text data. If it fails, this is a data-less record. */ + if (!copy_data(&rb->text_data_ring, &desc.text_blk_lpos, desc.info.text_len, + r->text_buf, r->text_buf_size, line_count)) { + return -ENOENT; + } + + /* + * Copy dict data. Although this should not fail, dict data is not + * important. So if it fails, modify the copied meta data to report + * that there is no dict data, thus silently dropping the dict data. + */ + if (!copy_data(&rb->dict_data_ring, &desc.dict_blk_lpos, desc.info.dict_len, + r->dict_buf, r->dict_buf_size, NULL)) { + if (r->info) + r->info->dict_len = 0; + } + + /* Ensure the record is still committed and has the same @seq. */ + return desc_read_committed_seq(desc_ring, id, seq, &desc); +} + +/* Get the sequence number of the tail descriptor. */ +static u64 prb_first_seq(struct printk_ringbuffer *rb) +{ + struct prb_desc_ring *desc_ring = &rb->desc_ring; + enum desc_state d_state; + struct prb_desc desc; + unsigned long id; + + for (;;) { + id = atomic_long_read(&rb->desc_ring.tail_id); /* LMM(prb_first_seq:A) */ + + d_state = desc_read(desc_ring, id, &desc); /* LMM(prb_first_seq:B) */ + + /* + * This loop will not be infinite because the tail is + * _always_ in the committed or reusable state. + */ + if (d_state == desc_committed || d_state == desc_reusable) + break; + + /* + * Guarantee the last state load from desc_read() is before + * reloading @tail_id in order to see a new tail in the case + * that the descriptor has been recycled. This pairs with + * desc_reserve:D. + * + * Memory barrier involvement: + * + * If prb_first_seq:B reads from desc_reserve:F, then + * prb_first_seq:A reads from desc_push_tail:B. + * + * Relies on: + * + * MB from desc_push_tail:B to desc_reserve:F + * matching + * RMB prb_first_seq:B to prb_first_seq:A + */ + smp_rmb(); /* LMM(prb_first_seq:C) */ + } + + return desc.info.seq; +} + +/* + * Non-blocking read of a record. Updates @seq to the last committed record + * (which may have no data). + * + * See the description of prb_read_valid() and prb_read_valid_info() + * for details. + */ +static bool _prb_read_valid(struct printk_ringbuffer *rb, u64 *seq, + struct printk_record *r, unsigned int *line_count) +{ + u64 tail_seq; + int err; + + while ((err = prb_read(rb, *seq, r, line_count))) { + tail_seq = prb_first_seq(rb); + + if (*seq < tail_seq) { + /* + * Behind the tail. Catch up and try again. This + * can happen for -ENOENT and -EINVAL cases. + */ + *seq = tail_seq; + + } else if (err == -ENOENT) { + /* Record exists, but no data available. Skip. */ + (*seq)++; + + } else { + /* Non-existent/non-committed record. Must stop. */ + return false; + } + } + + return true; +} + +/** + * prb_read_valid() - Non-blocking read of a requested record or (if gone) + * the next available record. + * + * @rb: The ringbuffer to read from. + * @seq: The sequence number of the record to read. + * @r: A record data buffer to store the read record to. + * + * This is the public function available to readers to read a record. + * + * The reader provides the @info, @text_buf, @dict_buf buffers of @r to be + * filled in. Any of the buffer pointers can be set to NULL if the reader + * is not interested in that data. To ensure proper initialization of @r, + * prb_rec_init_rd() should be used. + * + * Context: Any context. + * Return: true if a record was read, otherwise false. + * + * On success, the reader must check r->info.seq to see which record was + * actually read. This allows the reader to detect dropped records. + * + * Failure means @seq refers to a not yet written record. + */ +bool prb_read_valid(struct printk_ringbuffer *rb, u64 seq, + struct printk_record *r) +{ + return _prb_read_valid(rb, &seq, r, NULL); +} + +/** + * prb_read_valid_info() - Non-blocking read of meta data for a requested + * record or (if gone) the next available record. + * + * @rb: The ringbuffer to read from. + * @seq: The sequence number of the record to read. + * @info: A buffer to store the read record meta data to. + * @line_count: A buffer to store the number of lines in the record text. + * + * This is the public function available to readers to read only the + * meta data of a record. + * + * The reader provides the @info, @line_count buffers to be filled in. + * Either of the buffer pointers can be set to NULL if the reader is not + * interested in that data. + * + * Context: Any context. + * Return: true if a record's meta data was read, otherwise false. + * + * On success, the reader must check info->seq to see which record meta data + * was actually read. This allows the reader to detect dropped records. + * + * Failure means @seq refers to a not yet written record. + */ +bool prb_read_valid_info(struct printk_ringbuffer *rb, u64 seq, + struct printk_info *info, unsigned int *line_count) +{ + struct printk_record r; + + prb_rec_init_rd(&r, info, NULL, 0, NULL, 0); + + return _prb_read_valid(rb, &seq, &r, line_count); +} + +/** + * prb_first_valid_seq() - Get the sequence number of the oldest available + * record. + * + * @rb: The ringbuffer to get the sequence number from. + * + * This is the public function available to readers to see what the + * first/oldest valid sequence number is. + * + * This provides readers a starting point to begin iterating the ringbuffer. + * + * Context: Any context. + * Return: The sequence number of the first/oldest record or, if the + * ringbuffer is empty, 0 is returned. + */ +u64 prb_first_valid_seq(struct printk_ringbuffer *rb) +{ + u64 seq = 0; + + if (!_prb_read_valid(rb, &seq, NULL, NULL)) + return 0; + + return seq; +} + +/** + * prb_next_seq() - Get the sequence number after the last available record. + * + * @rb: The ringbuffer to get the sequence number from. + * + * This is the public function available to readers to see what the next + * newest sequence number available to readers will be. + * + * This provides readers a sequence number to jump to if all currently + * available records should be skipped. + * + * Context: Any context. + * Return: The sequence number of the next newest (not yet available) record + * for readers. + */ +u64 prb_next_seq(struct printk_ringbuffer *rb) +{ + u64 seq = 0; + + /* Search forward from the oldest descriptor. */ + while (_prb_read_valid(rb, &seq, NULL, NULL)) + seq++; + + return seq; +} + +/** + * prb_init() - Initialize a ringbuffer to use provided external buffers. + * + * @rb: The ringbuffer to initialize. + * @text_buf: The data buffer for text data. + * @textbits: The size of @text_buf as a power-of-2 value. + * @dict_buf: The data buffer for dictionary data. + * @dictbits: The size of @dict_buf as a power-of-2 value. + * @descs: The descriptor buffer for ringbuffer records. + * @descbits: The count of @descs items as a power-of-2 value. + * + * This is the public function available to writers to setup a ringbuffer + * during runtime using provided buffers. + * + * This must match the initialization of DEFINE_PRINTKRB(). + * + * Context: Any context. + */ +void prb_init(struct printk_ringbuffer *rb, + char *text_buf, unsigned int textbits, + char *dict_buf, unsigned int dictbits, + struct prb_desc *descs, unsigned int descbits) +{ + memset(descs, 0, _DESCS_COUNT(descbits) * sizeof(descs[0])); + + rb->desc_ring.count_bits = descbits; + rb->desc_ring.descs = descs; + atomic_long_set(&rb->desc_ring.head_id, DESC0_ID(descbits)); + atomic_long_set(&rb->desc_ring.tail_id, DESC0_ID(descbits)); + + rb->text_data_ring.size_bits = textbits; + rb->text_data_ring.data = text_buf; + atomic_long_set(&rb->text_data_ring.head_lpos, BLK0_LPOS(textbits)); + atomic_long_set(&rb->text_data_ring.tail_lpos, BLK0_LPOS(textbits)); + + rb->dict_data_ring.size_bits = dictbits; + rb->dict_data_ring.data = dict_buf; + atomic_long_set(&rb->dict_data_ring.head_lpos, BLK0_LPOS(dictbits)); + atomic_long_set(&rb->dict_data_ring.tail_lpos, BLK0_LPOS(dictbits)); + + atomic_long_set(&rb->fail, 0); + + descs[0].info.seq = -(u64)_DESCS_COUNT(descbits); + + descs[_DESCS_COUNT(descbits) - 1].info.seq = 0; + atomic_long_set(&(descs[_DESCS_COUNT(descbits) - 1].state_var), DESC0_SV(descbits)); + descs[_DESCS_COUNT(descbits) - 1].text_blk_lpos.begin = INVALID_LPOS; + descs[_DESCS_COUNT(descbits) - 1].text_blk_lpos.next = INVALID_LPOS; + descs[_DESCS_COUNT(descbits) - 1].dict_blk_lpos.begin = INVALID_LPOS; + descs[_DESCS_COUNT(descbits) - 1].dict_blk_lpos.next = INVALID_LPOS; +} + +/** + * prb_record_text_space() - Query the full actual used ringbuffer space for + * the text data of a reserved entry. + * + * @e: The successfully reserved entry to query. + * + * This is the public function available to writers to see how much actual + * space is used in the ringbuffer to store the text data of the specified + * entry. + * + * This function is only valid if @e has been successfully reserved using + * prb_reserve(). + * + * Context: Any context. + * Return: The size in bytes used by the text data of the associated record. + */ +unsigned int prb_record_text_space(struct prb_reserved_entry *e) +{ + return e->text_space; +} diff --git a/kernel/printk/printk_ringbuffer.h b/kernel/printk/printk_ringbuffer.h new file mode 100644 index 000000000000..3e46a7423c13 --- /dev/null +++ b/kernel/printk/printk_ringbuffer.h @@ -0,0 +1,399 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#ifndef _KERNEL_PRINTK_RINGBUFFER_H +#define _KERNEL_PRINTK_RINGBUFFER_H + +#include <linux/atomic.h> + +/* + * Meta information about each stored message. + * + * All fields are set and used by the printk code except for + * @seq, @text_len, @dict_len, which are set and/or modified + * by the ringbuffer code. + */ +struct printk_info { + u64 seq; /* sequence number */ + u64 ts_nsec; /* timestamp in nanoseconds */ + u16 text_len; /* length of text message */ + u16 dict_len; /* length of dictionary message */ + u8 facility; /* syslog facility */ + u8 flags:5; /* internal record flags */ + u8 level:3; /* syslog level */ + u32 caller_id; /* thread id or processor id */ +}; + +/* + * A structure providing the buffers, used by writers and readers. + * + * Writers: + * Using prb_rec_init_wr(), a writer sets @text_buf_size and @dict_buf_size + * before calling prb_reserve(). On success, prb_reserve() sets @info, + * @text_buf, @dict_buf to buffers reserved for that writer. + * + * Readers: + * Using prb_rec_init_rd(), a reader sets all fields before calling + * prb_read_valid(). Note that the reader provides the @info, @text_buf, + * @dict_buf buffers. On success, the struct pointed to by @info will be + * filled and the char arrays pointed to by @text_buf and @dict_buf will + * be filled with text and dict data. + */ +struct printk_record { + struct printk_info *info; + char *text_buf; + char *dict_buf; + unsigned int text_buf_size; + unsigned int dict_buf_size; +}; + +/* Specifies the logical position and span of a data block. */ +struct prb_data_blk_lpos { + unsigned long begin; + unsigned long next; +}; + +/* + * A descriptor: the complete meta-data for a record. + * + * @state_var: A bitwise combination of descriptor ID and descriptor state. + */ +struct prb_desc { + struct printk_info info; + atomic_long_t state_var; + struct prb_data_blk_lpos text_blk_lpos; + struct prb_data_blk_lpos dict_blk_lpos; +}; + +/* A ringbuffer of "ID + data" elements. */ +struct prb_data_ring { + unsigned int size_bits; + char *data; + atomic_long_t head_lpos; + atomic_long_t tail_lpos; +}; + +/* A ringbuffer of "struct prb_desc" elements. */ +struct prb_desc_ring { + unsigned int count_bits; + struct prb_desc *descs; + atomic_long_t head_id; + atomic_long_t tail_id; +}; + +/* + * The high level structure representing the printk ringbuffer. + * + * @fail: Count of failed prb_reserve() calls where not even a data-less + * record was created. + */ +struct printk_ringbuffer { + struct prb_desc_ring desc_ring; + struct prb_data_ring text_data_ring; + struct prb_data_ring dict_data_ring; + atomic_long_t fail; +}; + +/* + * Used by writers as a reserve/commit handle. + * + * @rb: Ringbuffer where the entry is reserved. + * @irqflags: Saved irq flags to restore on entry commit. + * @id: ID of the reserved descriptor. + * @text_space: Total occupied buffer space in the text data ring, including + * ID, alignment padding, and wrapping data blocks. + * + * This structure is an opaque handle for writers. Its contents are only + * to be used by the ringbuffer implementation. + */ +struct prb_reserved_entry { + struct printk_ringbuffer *rb; + unsigned long irqflags; + unsigned long id; + unsigned int text_space; +}; + +#define _DATA_SIZE(sz_bits) (1UL << (sz_bits)) +#define _DESCS_COUNT(ct_bits) (1U << (ct_bits)) +#define DESC_SV_BITS (sizeof(unsigned long) * 8) +#define DESC_COMMITTED_MASK (1UL << (DESC_SV_BITS - 1)) +#define DESC_REUSE_MASK (1UL << (DESC_SV_BITS - 2)) +#define DESC_FLAGS_MASK (DESC_COMMITTED_MASK | DESC_REUSE_MASK) +#define DESC_ID_MASK (~DESC_FLAGS_MASK) +#define DESC_ID(sv) ((sv) & DESC_ID_MASK) +#define INVALID_LPOS 1 + +#define INVALID_BLK_LPOS \ +{ \ + .begin = INVALID_LPOS, \ + .next = INVALID_LPOS, \ +} + +/* + * Descriptor Bootstrap + * + * The descriptor array is minimally initialized to allow immediate usage + * by readers and writers. The requirements that the descriptor array + * initialization must satisfy: + * + * Req1 + * The tail must point to an existing (committed or reusable) descriptor. + * This is required by the implementation of prb_first_seq(). + * + * Req2 + * Readers must see that the ringbuffer is initially empty. + * + * Req3 + * The first record reserved by a writer is assigned sequence number 0. + * + * To satisfy Req1, the tail initially points to a descriptor that is + * minimally initialized (having no data block, i.e. data-less with the + * data block's lpos @begin and @next values set to INVALID_LPOS). + * + * To satisfy Req2, the initial tail descriptor is initialized to the + * reusable state. Readers recognize reusable descriptors as existing + * records, but skip over them. + * + * To satisfy Req3, the last descriptor in the array is used as the initial + * head (and tail) descriptor. This allows the first record reserved by a + * writer (head + 1) to be the first descriptor in the array. (Only the first + * descriptor in the array could have a valid sequence number of 0.) + * + * The first time a descriptor is reserved, it is assigned a sequence number + * with the value of the array index. A "first time reserved" descriptor can + * be recognized because it has a sequence number of 0 but does not have an + * index of 0. (Only the first descriptor in the array could have a valid + * sequence number of 0.) After the first reservation, all future reservations + * (recycling) simply involve incrementing the sequence number by the array + * count. + * + * Hack #1 + * Only the first descriptor in the array is allowed to have the sequence + * number 0. In this case it is not possible to recognize if it is being + * reserved the first time (set to index value) or has been reserved + * previously (increment by the array count). This is handled by _always_ + * incrementing the sequence number by the array count when reserving the + * first descriptor in the array. In order to satisfy Req3, the sequence + * number of the first descriptor in the array is initialized to minus + * the array count. Then, upon the first reservation, it is incremented + * to 0, thus satisfying Req3. + * + * Hack #2 + * prb_first_seq() can be called at any time by readers to retrieve the + * sequence number of the tail descriptor. However, due to Req2 and Req3, + * initially there are no records to report the sequence number of + * (sequence numbers are u64 and there is nothing less than 0). To handle + * this, the sequence number of the initial tail descriptor is initialized + * to 0. Technically this is incorrect, because there is no record with + * sequence number 0 (yet) and the tail descriptor is not the first + * descriptor in the array. But it allows prb_read_valid() to correctly + * report the existence of a record for _any_ given sequence number at all + * times. Bootstrapping is complete when the tail is pushed the first + * time, thus finally pointing to the first descriptor reserved by a + * writer, which has the assigned sequence number 0. + */ + +/* + * Initiating Logical Value Overflows + * + * Both logical position (lpos) and ID values can be mapped to array indexes + * but may experience overflows during the lifetime of the system. To ensure + * that printk_ringbuffer can handle the overflows for these types, initial + * values are chosen that map to the correct initial array indexes, but will + * result in overflows soon. + * + * BLK0_LPOS + * The initial @head_lpos and @tail_lpos for data rings. It is at index + * 0 and the lpos value is such that it will overflow on the first wrap. + * + * DESC0_ID + * The initial @head_id and @tail_id for the desc ring. It is at the last + * index of the descriptor array (see Req3 above) and the ID value is such + * that it will overflow on the second wrap. + */ +#define BLK0_LPOS(sz_bits) (-(_DATA_SIZE(sz_bits))) +#define DESC0_ID(ct_bits) DESC_ID(-(_DESCS_COUNT(ct_bits) + 1)) +#define DESC0_SV(ct_bits) (DESC_COMMITTED_MASK | DESC_REUSE_MASK | DESC0_ID(ct_bits)) + +/* + * Define a ringbuffer with an external text data buffer. The same as + * DEFINE_PRINTKRB() but requires specifying an external buffer for the + * text data. + * + * Note: The specified external buffer must be of the size: + * 2 ^ (descbits + avgtextbits) + */ +#define _DEFINE_PRINTKRB(name, descbits, avgtextbits, avgdictbits, text_buf) \ +static char _##name##_dict[1U << ((avgdictbits) + (descbits))] \ + __aligned(__alignof__(unsigned long)); \ +static struct prb_desc _##name##_descs[_DESCS_COUNT(descbits)] = { \ + /* this will be the first record reserved by a writer */ \ + [0] = { \ + .info = { \ + /* will be incremented to 0 on the first reservation */ \ + .seq = -(u64)_DESCS_COUNT(descbits), \ + }, \ + }, \ + /* the initial head and tail */ \ + [_DESCS_COUNT(descbits) - 1] = { \ + .info = { \ + /* reports the first seq value during the bootstrap phase */ \ + .seq = 0, \ + }, \ + /* reusable */ \ + .state_var = ATOMIC_INIT(DESC0_SV(descbits)), \ + /* no associated data block */ \ + .text_blk_lpos = INVALID_BLK_LPOS, \ + .dict_blk_lpos = INVALID_BLK_LPOS, \ + }, \ +}; \ +static struct printk_ringbuffer name = { \ + .desc_ring = { \ + .count_bits = descbits, \ + .descs = &_##name##_descs[0], \ + .head_id = ATOMIC_INIT(DESC0_ID(descbits)), \ + .tail_id = ATOMIC_INIT(DESC0_ID(descbits)), \ + }, \ + .text_data_ring = { \ + .size_bits = (avgtextbits) + (descbits), \ + .data = text_buf, \ + .head_lpos = ATOMIC_LONG_INIT(BLK0_LPOS((avgtextbits) + (descbits))), \ + .tail_lpos = ATOMIC_LONG_INIT(BLK0_LPOS((avgtextbits) + (descbits))), \ + }, \ + .dict_data_ring = { \ + .size_bits = (avgtextbits) + (descbits), \ + .data = &_##name##_dict[0], \ + .head_lpos = ATOMIC_LONG_INIT(BLK0_LPOS((avgtextbits) + (descbits))), \ + .tail_lpos = ATOMIC_LONG_INIT(BLK0_LPOS((avgtextbits) + (descbits))), \ + }, \ + .fail = ATOMIC_LONG_INIT(0), \ +} + +/** + * DEFINE_PRINTKRB() - Define a ringbuffer. + * + * @name: The name of the ringbuffer variable. + * @descbits: The number of descriptors as a power-of-2 value. + * @avgtextbits: The average text data size per record as a power-of-2 value. + * @avgdictbits: The average dictionary data size per record as a + * power-of-2 value. + * + * This is a macro for defining a ringbuffer and all internal structures + * such that it is ready for immediate use. See _DEFINE_PRINTKRB() for a + * variant where the text data buffer can be specified externally. + */ +#define DEFINE_PRINTKRB(name, descbits, avgtextbits, avgdictbits) \ +static char _##name##_text[1U << ((avgtextbits) + (descbits))] \ + __aligned(__alignof__(unsigned long)); \ +_DEFINE_PRINTKRB(name, descbits, avgtextbits, avgdictbits, &_##name##_text[0]) + +/* Writer Interface */ + +/** + * prb_rec_init_wd() - Initialize a buffer for writing records. + * + * @r: The record to initialize. + * @text_buf_size: The needed text buffer size. + * @dict_buf_size: The needed dictionary buffer size. + * + * Initialize all the fields that a writer is interested in. If + * @dict_buf_size is 0, a dictionary buffer will not be reserved. + * @text_buf_size must be greater than 0. + * + * Note that although @dict_buf_size may be initialized to non-zero, + * its value must be rechecked after a successful call to prb_reserve() + * to verify a dictionary buffer was actually reserved. Dictionary buffer + * reservation is allowed to fail. + */ +static inline void prb_rec_init_wr(struct printk_record *r, + unsigned int text_buf_size, + unsigned int dict_buf_size) +{ + r->info = NULL; + r->text_buf = NULL; + r->dict_buf = NULL; + r->text_buf_size = text_buf_size; + r->dict_buf_size = dict_buf_size; +} + +bool prb_reserve(struct prb_reserved_entry *e, struct printk_ringbuffer *rb, + struct printk_record *r); +void prb_commit(struct prb_reserved_entry *e); + +void prb_init(struct printk_ringbuffer *rb, + char *text_buf, unsigned int text_buf_size, + char *dict_buf, unsigned int dict_buf_size, + struct prb_desc *descs, unsigned int descs_count_bits); +unsigned int prb_record_text_space(struct prb_reserved_entry *e); + +/* Reader Interface */ + +/** + * prb_rec_init_rd() - Initialize a buffer for reading records. + * + * @r: The record to initialize. + * @info: A buffer to store record meta-data. + * @text_buf: A buffer to store text data. + * @text_buf_size: The size of @text_buf. + * @dict_buf: A buffer to store dictionary data. + * @dict_buf_size: The size of @dict_buf. + * + * Initialize all the fields that a reader is interested in. All arguments + * (except @r) are optional. Only record data for arguments that are + * non-NULL or non-zero will be read. + */ +static inline void prb_rec_init_rd(struct printk_record *r, + struct printk_info *info, + char *text_buf, unsigned int text_buf_size, + char *dict_buf, unsigned int dict_buf_size) +{ + r->info = info; + r->text_buf = text_buf; + r->dict_buf = dict_buf; + r->text_buf_size = text_buf_size; + r->dict_buf_size = dict_buf_size; +} + +/** + * prb_for_each_record() - Iterate over the records of a ringbuffer. + * + * @from: The sequence number to begin with. + * @rb: The ringbuffer to iterate over. + * @s: A u64 to store the sequence number on each iteration. + * @r: A printk_record to store the record on each iteration. + * + * This is a macro for conveniently iterating over a ringbuffer. + * Note that @s may not be the sequence number of the record on each + * iteration. For the sequence number, @r->info->seq should be checked. + * + * Context: Any context. + */ +#define prb_for_each_record(from, rb, s, r) \ +for ((s) = from; prb_read_valid(rb, s, r); (s) = (r)->info->seq + 1) + +/** + * prb_for_each_info() - Iterate over the meta data of a ringbuffer. + * + * @from: The sequence number to begin with. + * @rb: The ringbuffer to iterate over. + * @s: A u64 to store the sequence number on each iteration. + * @i: A printk_info to store the record meta data on each iteration. + * @lc: An unsigned int to store the text line count of each record. + * + * This is a macro for conveniently iterating over a ringbuffer. + * Note that @s may not be the sequence number of the record on each + * iteration. For the sequence number, @r->info->seq should be checked. + * + * Context: Any context. + */ +#define prb_for_each_info(from, rb, s, i, lc) \ +for ((s) = from; prb_read_valid_info(rb, s, i, lc); (s) = (i)->seq + 1) + +bool prb_read_valid(struct printk_ringbuffer *rb, u64 seq, + struct printk_record *r); +bool prb_read_valid_info(struct printk_ringbuffer *rb, u64 seq, + struct printk_info *info, unsigned int *line_count); + +u64 prb_first_valid_seq(struct printk_ringbuffer *rb); +u64 prb_next_seq(struct printk_ringbuffer *rb); + +#endif /* _KERNEL_PRINTK_RINGBUFFER_H */ |