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* Staging: speakup: Update __speakup_paste_selection() tty (ab)usage to match vtBen Hutchings2014-05-241-0/+2
| | | | | | | | | | | | | | | | | | This function is largely a duplicate of paste_selection() in drivers/tty/vt/selection.c, but with its own selection state. The speakup selection mechanism should really be merged with vt. For now, apply the changes from 'TTY: vt, fix paste_selection ldisc handling', 'tty: Make ldisc input flow control concurrency-friendly', and 'tty: Fix unsafe vt paste_selection()'. References: https://bugs.debian.org/735202 References: https://bugs.debian.org/744015 Reported-by: Paul Gevers <elbrus@debian.org> Reported-and-tested-by: Jarek Czekalski <jarekczek@poczta.onet.pl> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> Cc: <stable@vger.kernel.org> # v3.8 but needs backporting for < 3.12 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Fix lockless tty buffer racePeter Hurley2014-05-031-3/+14
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Commit 6a20dbd6caa2358716136144bf524331d70b1e03, "tty: Fix race condition between __tty_buffer_request_room and flush_to_ldisc" correctly identifies an unsafe race condition between __tty_buffer_request_room() and flush_to_ldisc(), where the consumer flush_to_ldisc() prematurely advances the head before consuming the last of the data committed. For example: CPU 0 | CPU 1 __tty_buffer_request_room | flush_to_ldisc ... | ... | count = head->commit - head->read n = tty_buffer_alloc() | b->commit = b->used | b->next = n | | if (!count) /* T */ | if (head->next == NULL) /* F */ | buf->head = head->next In this case, buf->head has been advanced but head->commit may have been updated with a new value. Instead of reintroducing an unnecessary lock, fix the race locklessly. Read the commit-next pair in the reverse order of writing, which guarantees the commit value read is the latest value written if the head is advancing. Reported-by: Manfred Schlaegl <manfred.schlaegl@gmx.at> Cc: <stable@vger.kernel.org> # 3.12.x+ Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* Revert "tty: Fix race condition between __tty_buffer_request_room and ↵Peter Hurley2014-05-031-14/+2
| | | | | | | | | | | | | | | | flush_to_ldisc" This reverts commit 6a20dbd6caa2358716136144bf524331d70b1e03. Although the commit correctly identifies an unsafe race condition between __tty_buffer_request_room() and flush_to_ldisc(), the commit fixes the race with an unnecessary spinlock in a lockless algorithm. The follow-on commit, "tty: Fix lockless tty buffer race" fixes the race locklessly. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Fix race condition between __tty_buffer_request_room and flush_to_ldiscManfred Schlaegl2014-04-241-2/+14
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The race was introduced while development of linux-3.11 by e8437d7ecbc50198705331449367d401ebb3181f and e9975fdec0138f1b2a85b9624e41660abd9865d4. Originally it was found and reproduced on linux-3.12.15 and linux-3.12.15-rt25, by sending 500 byte blocks with 115kbaud to the target uart in a loop with 100 milliseconds delay. In short: 1. The consumer flush_to_ldisc is on to remove the head tty_buffer. 2. The producer adds a number of bytes, so that a new tty_buffer must be allocated and added by __tty_buffer_request_room. 3. The consumer removes the head tty_buffer element, without handling newly committed data. Detailed example: * Initial buffer: * Head, Tail -> 0: used=250; commit=250; read=240; next=NULL * Consumer: ''flush_to_ldisc'' * consumed 10 Byte * buffer: * Head, Tail -> 0: used=250; commit=250; read=250; next=NULL {{{ count = head->commit - head->read; // count = 0 if (!count) { // enter // INTERRUPTED BY PRODUCER -> if (head->next == NULL) break; buf->head = head->next; tty_buffer_free(port, head); continue; } }}} * Producer: tty_insert_flip_... 10 bytes + tty_flip_buffer_push * buffer: * Head, Tail -> 0: used=250; commit=250; read=250; next=NULL * added 6 bytes: head-element filled to maximum. * buffer: * Head, Tail -> 0: used=256; commit=250; read=250; next=NULL * added 4 bytes: __tty_buffer_request_room is called * buffer: * Head -> 0: used=256; commit=256; read=250; next=1 * Tail -> 1: used=4; commit=0; read=250 next=NULL * push (tty_flip_buffer_push) * buffer: * Head -> 0: used=256; commit=256; read=250; next=1 * Tail -> 1: used=4; commit=4; read=250 next=NULL * Consumer {{{ count = head->commit - head->read; if (!count) { // INTERRUPTED BY PRODUCER <- if (head->next == NULL) // -> no break break; buf->head = head->next; tty_buffer_free(port, head); // ERROR: tty_buffer head freed -> 6 bytes lost continue; } }}} This patch reintroduces a spin_lock to protect this case. Perhaps later a lock-less solution could be found. Signed-off-by: Manfred Schlaegl <manfred.schlaegl@gmx.at> Cc: stable <stable@vger.kernel.org> # 3.11 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Fix low_latency BUGPeter Hurley2014-02-281-16/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The user-settable knob, low_latency, has been the source of several BUG reports which stem from flush_to_ldisc() running in interrupt context. Since 3.12, which added several sleeping locks (termios_rwsem and buf->lock) to the input processing path, the frequency of these BUG reports has increased. Note that changes in 3.12 did not introduce this regression; sleeping locks were first added to the input processing path with the removal of the BKL from N_TTY in commit a88a69c91256418c5907c2f1f8a0ec0a36f9e6cc, 'n_tty: Fix loss of echoed characters and remove bkl from n_tty' and later in commit 38db89799bdf11625a831c5af33938dcb11908b6, 'tty: throttling race fix'. Since those changes, executing flush_to_ldisc() in interrupt_context (ie, low_latency set), is unsafe. However, since most devices do not validate if the low_latency setting is appropriate for the context (process or interrupt) in which they receive data, some reports are due to misconfiguration. Further, serial dma devices for which dma fails, resort to interrupt receiving as a backup without resetting low_latency. Historically, low_latency was used to force wake-up the reading process rather than wait for the next scheduler tick. The effect was to trim multiple milliseconds of latency from when the process would receive new data. Recent tests [1] have shown that the reading process now receives data with only 10's of microseconds latency without low_latency set. Remove the low_latency rx steering from tty_flip_buffer_push(); however, leave the knob as an optional hint to drivers that can tune their rx fifos and such like. Cleanup stale code comments regarding low_latency. [1] https://lkml.org/lkml/2014/2/20/434 "Yay.. thats an annoying historical pain in the butt gone." -- Alan Cox Reported-by: Beat Bolli <bbolli@ewanet.ch> Reported-by: Pavel Roskin <proski@gnu.org> Acked-by: David Sterba <dsterba@suse.cz> Cc: Grant Edwards <grant.b.edwards@gmail.com> Cc: Stanislaw Gruszka <sgruszka@redhat.com> Cc: Hal Murray <murray+fedora@ip-64-139-1-69.sjc.megapath.net> Cc: <stable@vger.kernel.org> # 3.12.x+ Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: delete non-required instances of include <linux/init.h>Paul Gortmaker2014-01-071-1/+0
| | | | | | | | | | None of these files are actually using any __init type directives and hence don't need to include <linux/init.h>. Most are just a left over from __devinit and __cpuinit removal, or simply due to code getting copied from one driver to the next. Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Halve flip buffer GFP_ATOMIC memory consumptionPeter Hurley2013-12-091-10/+35
| | | | | | | | | | | | | tty flip buffers use GFP_ATOMIC allocations for received data which is to be processed by the line discipline. For each byte received, an extra byte is used to indicate the error status of that byte. Instead, if the received data is error-free, encode the entire buffer without status bytes. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Fix stale tty_buffer_flush() commentPeter Hurley2013-12-081-3/+1
| | | | | | | | | | | Commit d7a68be4f265be10e24be931c257af30ca55566b, 'tty: Only perform flip buffer flush from tty_buffer_flush()', removed buffer flushing from flush_to_ldisc(). Fix function header comment which describes the former behavior. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* staging/fwserial: Rip out rx bufferingPeter Hurley2013-12-081-0/+1
| | | | | Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Remove tty_prepare_flip_string_flags()Peter Hurley2013-12-081-28/+0
| | | | | | | There is no in-tree user of tty_prepare_flip_string_flags(); remove. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Rename tty buffer memory_used fieldPeter Hurley2013-12-081-6/+6
| | | | | | | Trim up the memory_used field name to mem_used. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Enable configurable tty flip buffer limitPeter Hurley2013-12-081-3/+21
| | | | | | | | | | | Allow driver to configure its maximum flip buffer memory consumption/limit. This is necessary for very-high speed line rates (in excess of 10MB/sec) because the flip buffers can be saturated before the line discipline has a chance to throttle the input. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Remove private constant from global namespacePeter Hurley2013-07-231-0/+10
| | | | | | | | TTY_BUFFER_PAGE is only used within drivers/tty/tty_buffer.c; relocate to that file scope. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Fix unsafe vt paste_selection()Peter Hurley2013-07-231-13/+48
| | | | | | | | | | Convert the tty_buffer_flush() exclusion mechanism to a public interface - tty_buffer_lock/unlock_exclusive() - and use the interface to safely write the paste selection to the line discipline. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Merge __tty_flush_buffer() into lone call sitePeter Hurley2013-07-231-23/+6
| | | | | | | | __tty_flush_buffer() is now only called by tty_flush_buffer(); merge functions. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Use non-atomic state to signal flip buffer flush pendingPeter Hurley2013-07-231-3/+4
| | | | | | | | | | | Atomic bit ops are no longer required to indicate a flip buffer flush is pending, as the flush_mutex is sufficient barrier. Remove the unnecessary port .iflags field and localize flip buffer state to struct tty_bufhead. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Only perform flip buffer flush from tty_buffer_flush()Peter Hurley2013-07-231-42/+21
| | | | | | | | | | | | Now that dropping the buffer lock is not necessary (as result of converting the spin lock to a mutex), the flip buffer flush no longer needs to be handled by the buffer work. Simply signal a flush is required; the buffer work will exit the i/o loop, which allows tty_buffer_flush() to proceed. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Ensure single-threaded flip buffer consumer with mutexPeter Hurley2013-07-231-21/+19
| | | | | | | | | | | The buffer work may race with parallel tty_buffer_flush. Use a mutex to guarantee exclusive modify access to the head flip buffer. Remove the unneeded spin lock. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Make driver-side flip buffers locklessPeter Hurley2013-07-231-27/+4
| | | | | | | | | | | Driver-side flip buffer input is already single-threaded; 'publish' the .next link as the last operation on the tail buffer so the 'consumer' sees the already-completed flip buffer. The commit buffer index is already 'published' by driver-side functions. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Track flip buffer memory limit atomicallyPeter Hurley2013-07-231-6/+31
| | | | | | | | | | | | Lockless flip buffers require atomically updating the bytes-in-use watermark. The pty driver also peeks at the watermark value to limit memory consumption to a much lower value than the default; query the watermark with new fn, tty_buffer_space_avail(). Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Simplify flip buffer list with 0-sized sentinelPeter Hurley2013-07-231-31/+18
| | | | | | | | | | | | | | | Use a 0-sized sentinel to avoid assigning the head ptr from the driver side thread. This also eliminates testing head/tail for NULL. When the sentinel is first 'consumed' by the buffer work (or by tty_buffer_flush()), it is detached from the list but not freed nor added to the free list. Both buffer work and tty_buffer_flush() continue to preserve at least 1 flip buffer to which head & tail is pointed. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Use lockless flip buffer free listPeter Hurley2013-07-231-17/+12
| | | | | | | | | | | | In preparation for lockless flip buffers, make the flip buffer free list lockless. NB: using llist is not the optimal solution, as the driver and buffer work may contend over the llist head unnecessarily. However, test measurements indicate this contention is low. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Use generic names for flip buffer list cursorsPeter Hurley2013-07-231-10/+10
| | | | | Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Merge tty_buffer_find() into tty_buffer_alloc()Peter Hurley2013-07-231-32/+18
| | | | | | | | | tty_buffer_find() implements a simple free list lookaside cache. Merge this functionality into tty_buffer_alloc() to reflect the more traditional alloc/free symmetry. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Factor flip buffer initialization into helper functionPeter Hurley2013-07-231-9/+12
| | | | | | | Factor shared code; prepare for adding 0-sized sentinel flip buffer. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Fix flip buffer free listPeter Hurley2013-07-231-6/+10
| | | | | | | | | | | Since flip buffers are size-aligned to 256 bytes and all flip buffers 512-bytes or larger are not added to the free list, the free list only contains 256-byte flip buffers. Remove the list search when allocating a new flip buffer. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Compute flip buffer ptrsPeter Hurley2013-07-231-12/+10
| | | | | | | | | | The char_buf_ptr and flag_buf_ptr values are trivially derived from the .data field offset; compute values as needed. Fixes a long-standing type-mismatch with the char and flag ptrs. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Make ldisc input flow control concurrency-friendlyPeter Hurley2013-07-231-4/+9
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | Although line discipline receiving is single-producer/single-consumer, using tty->receive_room to manage flow control creates unnecessary critical regions requiring additional lock use. Instead, introduce the optional .receive_buf2() ldisc method which returns the # of bytes actually received. Serialization is guaranteed by the caller. In turn, the line discipline should schedule the buffer work item whenever space becomes available; ie., when there is room to receive data and receive_room() previously returned 0 (the buffer work item stops processing if receive_buf2() returns 0). Note the 'no room' state need not be atomic despite concurrent use by two threads because only the buffer work thread can set the state and only the read() thread can clear the state. Add n_tty_receive_buf2() as the receive_buf2() method for N_TTY. Provide a public helper function, tty_ldisc_receive_buf(), to use when directly accessing the receive_buf() methods. Line disciplines not using input flow control can continue to set tty->receive_room to a fixed value and only provide the receive_buf() method. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Simplify tty buffer/ldisc interface with helper functionPeter Hurley2013-07-231-12/+17
| | | | | | | | | | | | | | | | | | | | | | Ldisc interface functions must be called with interrupts enabled. Separating the ldisc calls into a helper function simplies the eventual removal of the spinlock. Note that access to the buf->head ptr outside the spinlock is safe here because; * __tty_buffer_flush() is prevented from running while buffer work performs i/o, * tty_buffer_find() only assigns buf->head if the flip buffer list is empty (which is never the case in flush_to_ldisc() since at least one buffer is always left in the list after use) Access to the read index outside the spinlock is safe here for the same reasons. Update the buffer's read index _after_ the data has been received by the ldisc. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Replace ldisc locking with ldisc_semPeter Hurley2013-07-231-1/+1
| | | | | | | | | | | | | | | | | | | | | | Line discipline locking was performed with a combination of a mutex, a status bit, a count, and a waitqueue -- basically, a rw semaphore. Replace the existing combination with an ld_semaphore. Fixes: 1) the 'reference acquire after ldisc locked' bug 2) the over-complicated halt mechanism 3) lock order wrt. tty_lock() 4) dropping locks while changing ldisc 5) previously unidentified deadlock while locking ldisc from both linked ttys concurrently 6) previously unidentified recursive deadlocks Adds much-needed lockdep diagnostics. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Fix race condition if flushing tty flip buffersPeter Hurley2013-04-091-12/+10
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | As Ilya Zykov identified in his patch 'PROBLEM: Race condition in tty buffer's function flush_to_ldisc()', a race condition exists which allows a parallel flush_to_ldisc() to flush and free the tty flip buffers while those buffers are in-use. For example, CPU 0 | CPU 1 | CPU 2 | flush_to_ldisc() | | grab spin lock | tty_buffer_flush() | | flush_to_ldisc() wait for spin lock | | wait for spin lock | if (!test_and_set_bit(TTYP_FLUSHING)) | | while (next flip buffer) | | ... | | drop spin lock | grab spin lock | | if (test_bit(TTYP_FLUSHING)) | | set_bit(TTYP_FLUSHPENDING) | receive_buf() | drop spin lock | | | | grab spin lock | | if (!test_and_set_bit(TTYP_FLUSHING)) | | if (test_bit(TTYP_FLUSHPENDING)) | | __tty_buffer_flush() CPU 2 has just flushed and freed all tty flip buffers while CPU 1 is transferring data from the head flip buffer. The original patch was rejected under the assumption that parallel flush_to_ldisc() was not possible. Because of necessary changes to the workqueue api, work items can execute in parallel on SMP. This patch differs slightly from the original patch by testing for a pending flush _after_ each receive_buf(), since TTYP_FLUSHPENDING can only be set while the lock is dropped around receive_buf(). Reported-by: Ilya Zykov <linux@izyk.ru> Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Acked-by: Ilya Zykov <linux@izyk.ru> Cc: Jiri Slaby <jslaby@suse.cz> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* TTY: disable debugging warningJiri Slaby2013-03-041-1/+1
| | | | | | | | | | | | | | | We added a warning to flush_to_ldisc to report cases when it is called with a NULL tty. It was for debugging purposes and it lead to a patchset from Peter Hurley. The patchset however did not make it to 3.9, so disable the warning now to not disturb people. We can re-add it when the series is in and we are hunting for another bugs. Reported-by: David Miller <davem@davemloft.net> Cc: stable <stable@vger.kernel.org> # 3.8 Signed-off-by: Jiri Slaby <jslaby@suse.cz> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* pps: Move timestamp read into PPS code properGeorge Spelvin2013-02-131-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | The PPS (Pulse-Per-Second) line discipline has developed a number of unhealthy attachments to core tty data and functions, ultimately leading to its breakage. The previous patches fixed the crashing. This one reduces coupling further by eliminating the timestamp parameter from the dcd_change ldisc method. This reduces header file linkage and makes the extension more generic, and the timestamp read is delayed only slightly, from just before the ldisc->ops->dcd_change method call to just after. Fix attendant build breakage in drivers/tty/n_tty.c drivers/tty/tty_buffer.c drivers/staging/speakup/selection.c drivers/staging/dgrp/dgrp_*.c Cc: William Hubbs <w.d.hubbs@gmail.com> Cc: Chris Brannon <chris@the-brannons.com> Cc: Kirk Reiser <kirk@braille.uwo.ca> Cc: Samuel Thibault <samuel.thibault@ens-lyon.org> Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: George Spelvin <linux@horizon.com> Acked-by: Rodolfo Giometti <giometti@enneenne.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: Correct tty buffer flush.Ilya Zykov2013-01-201-70/+22
| | | | | | | | | | | | | | | | | | The root of problem is carelessly zeroing pointer(in function __tty_buffer_flush()), when another thread can use it. It can be cause of "NULL pointer dereference". Main idea of the patch, this is never free last (struct tty_buffer) in the active buffer. Only flush the data for ldisc(buf->head->read = buf->head->commit). At that moment driver can collect(write) data in buffer without conflict. It is repeat behavior of flush_to_ldisc(), only without feeding data to ldisc. Also revert: commit c56a00a165712fd73081f40044b1e64407bb1875 tty: hold lock across tty buffer finding and buffer filling In order to delete the unneeded locks any more. Signed-off-by: Ilya Zykov <ilya@ilyx.ru> CC: Alan Cox <alan@lxorguk.ukuu.org.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* TTY: switch tty_schedule_flipJiri Slaby2013-01-151-4/+4
| | | | | | | | | | | | Now, we start converting tty buffer functions to actually use tty_port. This will allow us to get rid of the need of tty in many call sites. Only tty_port will needed and hence no more tty_port_tty_get in those paths. This is the last one: tty_schedule_flip Signed-off-by: Jiri Slaby <jslaby@suse.cz> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* TTY: switch tty_flip_buffer_pushJiri Slaby2013-01-151-4/+4
| | | | | | | | | | | | | | | | | | | | Now, we start converting tty buffer functions to actually use tty_port. This will allow us to get rid of the need of tty in many call sites. Only tty_port will needed and hence no more tty_port_tty_get in those paths. Now, the one where most of tty_port_tty_get gets removed: tty_flip_buffer_push. IOW we also closed all the races in drivers not using tty_port_tty_get at all yet. Also we move tty_flip_buffer_push declaration from include/linux/tty.h to include/linux/tty_flip.h to all others while we are changing it anyway. Signed-off-by: Jiri Slaby <jslaby@suse.cz> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* TTY: move low_latency to tty_portJiri Slaby2013-01-151-4/+5
| | | | | | | | | | One point is to have less places where we actually need tty pointer. The other is that low_latency is bound to buffer processing and buffers are now in tty_port. So it makes sense to move low_latency to tty_port too. Signed-off-by: Jiri Slaby <jslaby@suse.cz> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* TTY: convert more flipping functionsJiri Slaby2013-01-151-16/+16
| | | | | | | | | | | | | | | | Now, we start converting tty buffer functions to actually use tty_port. This will allow us to get rid of the need of tty pointer in many call sites. Only tty_port will be needed and hence no more tty_port_tty_get calls in those paths. Now 4 string flipping ones are on turn: * tty_insert_flip_string_flags * tty_insert_flip_string_fixed_flag * tty_prepare_flip_string * tty_prepare_flip_string_flags Signed-off-by: Jiri Slaby <jslaby@suse.cz> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* TTY: switch tty_buffer_request_room to tty_portJiri Slaby2013-01-151-3/+2
| | | | | | | | | | | | Now, we start converting tty buffer functions to actually use tty_port. This will allow us to get rid of the need of tty pointer in many call sites. Only tty_port will be needed and hence no more tty_port_tty_get calls in those paths. Here we start with tty_buffer_request_room. Signed-off-by: Jiri Slaby <jslaby@suse.cz> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: add missing newlines to WARN_RATELIMITSasha Levin2012-10-251-1/+1
| | | | | | | | | | | | WARN_RATELIMIT() expects the warning to end with a newline if one is needed. Not doing so results in odd looking warnings such as: [ 1339.454272] tty is NULLPid: 7147, comm: kworker/4:0 Tainted: G W 3.7.0-rc2-next-20121025-sasha-00001-g673f98e-dirty #75 Signed-off-by: Sasha Levin <sasha.levin@oracle.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* TTY: Report warning when low_latency flag is wrongly usedIvo Sieben2012-10-241-0/+1
| | | | | | | | | | | | | | When a driver has the low_latency flag set and uses the schedule_flip() function to initiate copying data to the line discipline, a workqueue is scheduled in but never actually flushed. This is incorrect use of the low_latency flag (driver should not support the low_latency flag, or use the tty_flip_buffer_push() function instead). Make sure a warning is reported to catch incorrect use of the low_latency flag. This patch goes with: cee4ad1ed90a0959fc29f9d30a2526e5e9522cfa Signed-off-by: Ivo Sieben <meltedpianoman@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* TTY: move tty buffers to tty_portJiri Slaby2012-10-221-49/+53
| | | | | | | | | | | | | | | | | | | So this is it. The big step why we did all the work over the past kernel releases. Now everything is prepared, so nothing protects us from doing that big step. | | \ \ nnnn/^l | | | | \ / / | | | '-,.__ => \/ ,-` => | '-,.__ | O __.´´) ( .` | O __.´´) ~~~ ~~ `` ~~~ ~~ The buffers are now in the tty_port structure and we can start teaching the buffer helpers (insert char/string, flip etc.) to use tty_port instead of tty_struct all around. Signed-off-by: Jiri Slaby <jslaby@suse.cz> Acked-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* TTY: tty_buffer, cache pointer to tty->bufJiri Slaby2012-10-221-56/+76
| | | | | | | | | | | | | | | During the move of tty buffers from tty_struct to tty_port, we will need to switch all users of buf to tty->port->buf. There are many functions where this is accessed directly in their code many times. Cache the tty->buf pointer in such functions now and change only single lines in each function in the next patch. Not that it is convenient for the next patch, but the code is now also more readable. Signed-off-by: Jiri Slaby <jslaby@suse.cz> Acked-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* TTY: move TTY_FLUSH* flags to tty_portJiri Slaby2012-10-221-8/+10
| | | | | | | | | | | They are only TTY buffers specific. And the buffers will go to tty_port in the next patches. So to remove the need to have both tty_port and tty_struct at some places, let us move the flags to tty_port. Signed-off-by: Jiri Slaby <jslaby@suse.cz> Acked-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: prevent unnecessary work queue lock checking on flip buffer copyIvo Sieben2012-10-221-1/+4
| | | | | | | | | | | | | | | | When low_latency flag is set the TTY receive flip buffer is copied to the line discipline directly instead of using a work queue in the background. Therefor only in case a workqueue is actually used for copying data to the line discipline we'll have to flush the workqueue. This prevents unnecessary spin lock/unlock on the workqueue spin lock that can cause additional scheduling overhead on a PREEMPT_RT system. On a 200 MHz AT91SAM9261 processor setup this fixes about 100us of scheduling overhead on the TTY read call. Signed-off-by: Ivo Sieben <meltedpianoman@gmail.com> Acked-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty: hold lock across tty buffer finding and buffer fillingXiaobing Tu2012-04-091-20/+65
| | | | | | | | | | | | | tty_buffer_request_room is well protected, but while after it returns, it releases the port->lock. tty->buf.tail might be modified by either irq handler or other threads. The patch adds more protection by holding the lock across tty buffer finding and buffer filling. Signed-off-by: Alek Du <alek.du@intel.com> Signed-off-by: Xiaobing Tu <xiaobing.tu@intel.com> Cc: Jiri Slaby <jslaby@suse.cz> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* tty_buffer: get rid of 'seen_tail' logic in flush_to_ldiscLinus Torvalds2011-06-081-12/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The flush_to_ldisc() work entry has special logic to notice when it has seen the original tail of the data queue, and it avoids continuing the flush if it sees that _original_ tail rather than the current tail. This logic can trigger in case somebody is constantly adding new data to the tty while the flushing is active - and the intent is to avoid excessive CPU usage while flushing the tty, especially as we used to do this from a softirq context which made it non-preemptible. However, since we no longer re-arm the work-queue from within itself (because that causes other trouble: see commit a5660b41af6a "tty: fix endless work loop when the buffer fills up"), this just leads to possible hung tty's (most easily seen in SMP and with a test-program that floods a pty with data - nobody seems to have reported this for any real-life situation yet). And since the workqueue isn't done from timers and softirq's any more, it's doubtful whether the CPU useage issue is really relevant any more. So just remove the logic entirely, and see if anybody ever notices. Alternatively, we might want to re-introduce the "re-arm the work" for just this case, but then we'd have to re-introduce the delayed work model or some explicit timer, which really doesn't seem worth it for this. Reported-and-tested-by: Guillaume Chazarain <guichaz@gmail.com> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk> Cc: Felipe Balbi <balbi@ti.com> Cc: Greg Kroah-Hartman <gregkh@suse.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* Revert "tty: make receive_buf() return the amout of bytes received"Linus Torvalds2011-06-041-9/+6
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This reverts commit b1c43f82c5aa265442f82dba31ce985ebb7aa71c. It was broken in so many ways, and results in random odd pty issues. It re-introduced the buggy schedule_work() in flush_to_ldisc() that can cause endless work-loops (see commit a5660b41af6a: "tty: fix endless work loop when the buffer fills up"). It also used an "unsigned int" return value fo the ->receive_buf() function, but then made multiple functions return a negative error code, and didn't actually check for the error in the caller. And it didn't actually work at all. BenH bisected down odd tty behavior to it: "It looks like the patch is causing some major malfunctions of the X server for me, possibly related to PTYs. For example, cat'ing a large file in a gnome terminal hangs the kernel for -minutes- in a loop of what looks like flush_to_ldisc/workqueue code, (some ftrace data in the quoted bits further down). ... Some more data: It -looks- like what happens is that the flush_to_ldisc work queue entry constantly re-queues itself (because the PTY is full ?) and the workqueue thread will basically loop forver calling it without ever scheduling, thus starving the consumer process that could have emptied the PTY." which is pretty much exactly the problem we fixed in a5660b41af6a. Milton Miller pointed out the 'unsigned int' issue. Reported-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> Reported-by: Milton Miller <miltonm@bga.com> Cc: Stefan Bigler <stefan.bigler@keymile.com> Cc: Toby Gray <toby.gray@realvnc.com> Cc: Felipe Balbi <balbi@ti.com> Cc: Greg Kroah-Hartman <gregkh@suse.de> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* tty: make receive_buf() return the amout of bytes receivedFelipe Balbi2011-04-221-6/+9
| | | | | | | | | | | | | it makes it simpler to keep track of the amount of bytes received and simplifies how flush_to_ldisc counts the remaining bytes. It also fixes a bug of lost bytes on n_tty when flushing too many bytes via the USB serial gadget driver. Tested-by: Stefan Bigler <stefan.bigler@keymile.com> Tested-by: Toby Gray <toby.gray@realvnc.com> Signed-off-by: Felipe Balbi <balbi@ti.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
* tty: fix endless work loop when the buffer fills upLinus Torvalds2011-04-041-3/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Commit f23eb2b2b285 ('tty: stop using "delayed_work" in the tty layer') ended up causing hung machines on UP with no preemption, because the work routine to flip the buffer data to the ldisc would endlessly re-arm itself if the destination buffer had filled up. With the delayed work, that only caused a timer-driving polling of the tty state every timer tick, but without the delay we just ended up with basically a busy loop instead. Stop the insane polling, and instead make the code that opens up the receive room re-schedule the buffer flip work. That's what we should have been doing anyway. This same "poll for tty room" issue is almost certainly also the cause of excessive kworker activity when idle reported by Dave Jones, who also reported "flush_to_ldisc executing 2500 times a second" back in Nov 2010: http://lkml.org/lkml/2010/11/30/592 which is that silly flushing done every timer tick. Wasting both power and CPU for no good reason. Reported-and-tested-by: Alexander Beregalov <a.beregalov@gmail.com> Reported-and-tested-by: Sitsofe Wheeler <sitsofe@yahoo.com> Cc: Greg KH <gregkh@suse.de> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk> Cc: Dave Jones <davej@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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