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* fscache: Fix race in fscache_op_complete() due to split atomic_sub & readkiran.modukuri2018-12-171-2/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | [ Upstream commit 3f2b7b9035107d6096ea438ea3d97dcf0481b6d2 ] The code in fscache_retrieval_complete is using atomic_sub followed by an atomic_read: atomic_sub(n_pages, &op->n_pages); if (atomic_read(&op->n_pages) <= 0) fscache_op_complete(&op->op, true); This causes two threads doing a decrement of n_pages to race with each other seeing the op->refcount 0 at same time - and they end up calling fscache_op_complete() in both the threads leading to an assertion failure. Fix this by using atomic_sub_return_relaxed() instead of two calls. Note that I'm using 'relaxed' rather than, say, 'release' as there aren't multiple variables that appear to need ordering across the release. The oops looks something like: FS-Cache: Assertion failed FS-Cache: 0 > 0 is false ... kernel BUG at /usr/src/linux-4.4.0/fs/fscache/operation.c:449! ... Workqueue: fscache_operation fscache_op_work_func [fscache] ... RIP: 0010:[<ffffffffc037eacd>] fscache_op_complete+0x10d/0x180 [fscache] ... Call Trace: [<ffffffffc1464cf9>] cachefiles_read_copier+0x3a9/0x410 [cachefiles] [<ffffffffc037e272>] fscache_op_work_func+0x22/0x50 [fscache] [<ffffffff81096da0>] process_one_work+0x150/0x3f0 [<ffffffff8109751a>] worker_thread+0x11a/0x470 [<ffffffff81808e59>] ? __schedule+0x359/0x980 [<ffffffff81097400>] ? rescuer_thread+0x310/0x310 [<ffffffff8109cdd6>] kthread+0xd6/0xf0 [<ffffffff8109cd00>] ? kthread_park+0x60/0x60 [<ffffffff8180d0cf>] ret_from_fork+0x3f/0x70 [<ffffffff8109cd00>] ? kthread_park+0x60/0x60 This seen this in 4.4.x kernels and the same bug affects fscache in latest upstreams kernels. Fixes: 1bb4b7f98f36 ("FS-Cache: The retrieval remaining-pages counter needs to be atomic_t") Signed-off-by: Kiran Kumar Modukuri <kiran.modukuri@gmail.com> Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Sasha Levin <sashal@kernel.org>
* fscache: Pass object size in rather than calling back for itDavid Howells2018-04-061-1/+2
| | | | | | | | | | | | | | Pass the object size in to fscache_acquire_cookie() and fscache_write_page() rather than the netfs providing a callback by which it can be received. This makes it easier to update the size of the object when a new page is written that extends the object. The current object size is also passed by fscache to the check_aux function, obviating the need to store it in the aux data. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Anna Schumaker <anna.schumaker@netapp.com> Tested-by: Steve Dickson <steved@redhat.com>
* fscache: Add more tracepointsDavid Howells2018-04-041-1/+2
| | | | | | | | | | | | | | | | | | | | | Add more tracepoints to fscache, including: (*) fscache_page - Tracks netfs pages known to fscache. (*) fscache_check_page - Tracks the netfs querying whether a page is pending storage. (*) fscache_wake_cookie - Tracks cookies being woken up after a page completes/aborts storage in the cache. (*) fscache_op - Tracks operations being initialised. (*) fscache_wrote_page - Tracks return of the backend write_page op. (*) fscache_gang_lookup - Tracks lookup of pages to be stored in the write operation. Signed-off-by: David Howells <dhowells@redhat.com>
* fscache: Add tracepointsDavid Howells2018-04-041-2/+16
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Add some tracepoints to fscache: (*) fscache_cookie - Tracks a cookie's usage count. (*) fscache_netfs - Logs registration of a network filesystem, including the pointer to the cookie allocated. (*) fscache_acquire - Logs cookie acquisition. (*) fscache_relinquish - Logs cookie relinquishment. (*) fscache_enable - Logs enablement of a cookie. (*) fscache_disable - Logs disablement of a cookie. (*) fscache_osm - Tracks execution of states in the object state machine. and cachefiles: (*) cachefiles_ref - Tracks a cachefiles object's usage count. (*) cachefiles_lookup - Logs result of lookup_one_len(). (*) cachefiles_mkdir - Logs result of vfs_mkdir(). (*) cachefiles_create - Logs result of vfs_create(). (*) cachefiles_unlink - Logs calls to vfs_unlink(). (*) cachefiles_rename - Logs calls to vfs_rename(). (*) cachefiles_mark_active - Logs an object becoming active. (*) cachefiles_wait_active - Logs a wait for an old object to be destroyed. (*) cachefiles_mark_inactive - Logs an object becoming inactive. (*) cachefiles_mark_buried - Logs the burial of an object. Signed-off-by: David Howells <dhowells@redhat.com>
* fscache: Pass the correct cancelled indications to fscache_op_complete()David Howells2018-04-041-1/+1
| | | | | | | | The last parameter to fscache_op_complete() is a bool indicating whether or not the operation was cancelled. A lot of the time the inverse value is given or no differentiation is made. Fix this. Signed-off-by: David Howells <dhowells@redhat.com>
* sched/wait, fs/fscache: Convert wait_on_atomic_t() usage to the new ↵Peter Zijlstra2018-03-201-1/+1
| | | | | | | | | | | | | | | | | | wait_var_event() API The old wait_on_atomic_t() is going to get removed, use the more flexible wait_var_event() API instead. No change in functionality. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: David Howells <dhowells@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
* fscache: Fix dead object requeueDavid Howells2017-01-311-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Under some circumstances, an fscache object can become queued such that it fscache_object_work_func() can be called once the object is in the OBJECT_DEAD state. This results in the kernel oopsing when it tries to invoke the handler for the state (which is hard coded to 0x2). The way this comes about is something like the following: (1) The object dispatcher is processing a work state for an object. This is done in workqueue context. (2) An out-of-band event comes in that isn't masked, causing the object to be queued, say EV_KILL. (3) The object dispatcher finishes processing the current work state on that object and then sees there's another event to process, so, without returning to the workqueue core, it processes that event too. It then follows the chain of events that initiates until we reach OBJECT_DEAD without going through a wait state (such as WAIT_FOR_CLEARANCE). At this point, object->events may be 0, object->event_mask will be 0 and oob_event_mask will be 0. (4) The object dispatcher returns to the workqueue processor, and in due course, this sees that the object's work item is still queued and invokes it again. (5) The current state is a work state (OBJECT_DEAD), so the dispatcher jumps to it - resulting in an OOPS. When I'm seeing this, the work state in (1) appears to have been either LOOK_UP_OBJECT or CREATE_OBJECT (object->oob_table is fscache_osm_lookup_oob). The window for (2) is very small: (A) object->event_mask is cleared whilst the event dispatch process is underway - though there's no memory barrier to force this to the top of the function. The window, therefore is from the time the object was selected by the workqueue processor and made requeueable to the time the mask was cleared. (B) fscache_raise_event() will only queue the object if it manages to set the event bit and the corresponding event_mask bit was set. The enqueuement is then deferred slightly whilst we get a ref on the object and get the per-CPU variable for workqueue congestion. This slight deferral slightly increases the probability by allowing extra time for the workqueue to make the item requeueable. Handle this by giving the dead state a processor function and checking the for the dead state address rather than seeing if the processor function is address 0x2. The dead state processor function can then set a flag to indicate that it's occurred and give a warning if it occurs more than once per object. If this race occurs, an oops similar to the following is seen (note the RIP value): BUG: unable to handle kernel NULL pointer dereference at 0000000000000002 IP: [<0000000000000002>] 0x1 PGD 0 Oops: 0010 [#1] SMP Modules linked in: ... CPU: 17 PID: 16077 Comm: kworker/u48:9 Not tainted 3.10.0-327.18.2.el7.x86_64 #1 Hardware name: HP ProLiant DL380 Gen9/ProLiant DL380 Gen9, BIOS P89 12/27/2015 Workqueue: fscache_object fscache_object_work_func [fscache] task: ffff880302b63980 ti: ffff880717544000 task.ti: ffff880717544000 RIP: 0010:[<0000000000000002>] [<0000000000000002>] 0x1 RSP: 0018:ffff880717547df8 EFLAGS: 00010202 RAX: ffffffffa0368640 RBX: ffff880edf7a4480 RCX: dead000000200200 RDX: 0000000000000002 RSI: 00000000ffffffff RDI: ffff880edf7a4480 RBP: ffff880717547e18 R08: 0000000000000000 R09: dfc40a25cb3a4510 R10: dfc40a25cb3a4510 R11: 0000000000000400 R12: 0000000000000000 R13: ffff880edf7a4510 R14: ffff8817f6153400 R15: 0000000000000600 FS: 0000000000000000(0000) GS:ffff88181f420000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000002 CR3: 000000000194a000 CR4: 00000000001407e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 Stack: ffffffffa0363695 ffff880edf7a4510 ffff88093f16f900 ffff8817faa4ec00 ffff880717547e60 ffffffff8109d5db 00000000faa4ec18 0000000000000000 ffff8817faa4ec18 ffff88093f16f930 ffff880302b63980 ffff88093f16f900 Call Trace: [<ffffffffa0363695>] ? fscache_object_work_func+0xa5/0x200 [fscache] [<ffffffff8109d5db>] process_one_work+0x17b/0x470 [<ffffffff8109e4ac>] worker_thread+0x21c/0x400 [<ffffffff8109e290>] ? rescuer_thread+0x400/0x400 [<ffffffff810a5acf>] kthread+0xcf/0xe0 [<ffffffff810a5a00>] ? kthread_create_on_node+0x140/0x140 [<ffffffff816460d8>] ret_from_fork+0x58/0x90 [<ffffffff810a5a00>] ? kthread_create_on_node+0x140/0x140 Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Jeremy McNicoll <jeremymc@redhat.com> Tested-by: Frank Sorenson <sorenson@redhat.com> Tested-by: Benjamin Coddington <bcodding@redhat.com> Reviewed-by: Benjamin Coddington <bcodding@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* FS-Cache: make check_consistency callback return intYan, Zheng2016-06-011-1/+1
| | | | | | | | | | | __fscache_check_consistency() calls check_consistency() callback and return the callback's return value. But the return type of check_consistency() is bool. So __fscache_check_consistency() return 1 if the cache is inconsistent. This is inconsistent with the document. Signed-off-by: Yan, Zheng <zyan@redhat.com> Acked-by: David Howells <dhowells@redhat.com>
* FS-Cache: Retain the netfs context in the retrieval op earlierDavid Howells2015-04-021-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Now that the retrieval operation may be disposed of by fscache_put_operation() before we actually set the context, the retrieval-specific cleanup operation can produce a NULL-pointer dereference when it tries to unconditionally clean up the netfs context. Given that it is expected that we'll get at least as far as the place where we currently set the context pointer and it is unlikely we'll go through the error handling paths prior to that point, retain the context right from the point that the retrieval op is allocated. Concomitant to this, we need to retain the cookie pointer in the retrieval op also so that we can call the netfs to release its context in the release method. In addition, we might now get into fscache_release_retrieval_op() with the op only initialised. To this end, set the operation to DEAD only after the release method has been called and skip the n_pages test upon cleanup if the op is still in the INITIALISED state. Without these changes, the following oops might be seen: BUG: unable to handle kernel NULL pointer dereference at 00000000000000b8 ... RIP: 0010:[<ffffffffa0089c98>] fscache_release_retrieval_op+0xae/0x100 ... Call Trace: [<ffffffffa0088560>] fscache_put_operation+0x117/0x2e0 [<ffffffffa008b8f5>] __fscache_read_or_alloc_pages+0x351/0x3ac [<ffffffffa00b761f>] __nfs_readpages_from_fscache+0x59/0xbf [nfs] [<ffffffffa00b06c5>] nfs_readpages+0x10c/0x185 [nfs] [<ffffffff81124925>] ? alloc_pages_current+0x119/0x13e [<ffffffff810ee5fd>] ? __page_cache_alloc+0xfb/0x10a [<ffffffff810f87f8>] __do_page_cache_readahead+0x188/0x22c [<ffffffff810f8b3a>] ondemand_readahead+0x29e/0x2af [<ffffffff810f8c92>] page_cache_sync_readahead+0x38/0x3a [<ffffffff810ef337>] generic_file_read_iter+0x1a2/0x55a [<ffffffffa00a9dff>] ? nfs_revalidate_mapping+0xd6/0x288 [nfs] [<ffffffffa00a6a23>] nfs_file_read+0x49/0x70 [nfs] [<ffffffff811363be>] new_sync_read+0x78/0x9c [<ffffffff81137164>] __vfs_read+0x13/0x38 [<ffffffff8113721e>] vfs_read+0x95/0x121 [<ffffffff811372f6>] SyS_read+0x4c/0x8a [<ffffffff81557a52>] system_call_fastpath+0x12/0x17 Signed-off-by: David Howells <dhowells@redhat.com> Reviewed-by: Steve Dickson <steved@redhat.com> Acked-by: Jeff Layton <jeff.layton@primarydata.com>
* FS-Cache: The operation cancellation method needs calling in more placesDavid Howells2015-04-021-0/+5
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Any time an incomplete operation is cancelled, the operation cancellation function needs to be called to clean up. This is currently being passed directly to some of the functions that might want to call it, but not all. Instead, pass the cancellation method pointer to the fscache_operation_init() and have that cache it in the operation struct. Further, plug in a dummy cancellation handler if the caller declines to set one as this allows us to call the function unconditionally (the extra overhead isn't worth bothering about as we don't expect to be calling this typically). The cancellation method must thence be called everywhere the CANCELLED state is set. Note that we call it *before* setting the CANCELLED state such that the method can use the old state value to guide its operation. fscache_do_cancel_retrieval() needs moving higher up in the sources so that the init function can use it now. Without this, the following oops may be seen: FS-Cache: Assertion failed FS-Cache: 3 == 0 is false ------------[ cut here ]------------ kernel BUG at ../fs/fscache/page.c:261! ... RIP: 0010:[<ffffffffa0089c1b>] fscache_release_retrieval_op+0x77/0x100 [<ffffffffa008853d>] fscache_put_operation+0x114/0x2da [<ffffffffa008b8c2>] __fscache_read_or_alloc_pages+0x358/0x3b3 [<ffffffffa00b761f>] __nfs_readpages_from_fscache+0x59/0xbf [nfs] [<ffffffffa00b06c5>] nfs_readpages+0x10c/0x185 [nfs] [<ffffffff81124925>] ? alloc_pages_current+0x119/0x13e [<ffffffff810ee5fd>] ? __page_cache_alloc+0xfb/0x10a [<ffffffff810f87f8>] __do_page_cache_readahead+0x188/0x22c [<ffffffff810f8b3a>] ondemand_readahead+0x29e/0x2af [<ffffffff810f8c92>] page_cache_sync_readahead+0x38/0x3a [<ffffffff810ef337>] generic_file_read_iter+0x1a2/0x55a [<ffffffffa00a9dff>] ? nfs_revalidate_mapping+0xd6/0x288 [nfs] [<ffffffffa00a6a23>] nfs_file_read+0x49/0x70 [nfs] [<ffffffff811363be>] new_sync_read+0x78/0x9c [<ffffffff81137164>] __vfs_read+0x13/0x38 [<ffffffff8113721e>] vfs_read+0x95/0x121 [<ffffffff811372f6>] SyS_read+0x4c/0x8a [<ffffffff81557a52>] system_call_fastpath+0x12/0x17 The assertion is showing that the remaining number of pages (n_pages) is not 0 when the operation is being released. Signed-off-by: David Howells <dhowells@redhat.com> Reviewed-by: Steve Dickson <steved@redhat.com> Acked-by: Jeff Layton <jeff.layton@primarydata.com>
* FS-Cache: Out of line fscache_operation_init()David Howells2015-04-021-21/+3
| | | | | | | | | Out of line fscache_operation_init() so that it can access internal FS-Cache features, such as stats, in a later commit. Signed-off-by: David Howells <dhowells@redhat.com> Reviewed-by: Steve Dickson <steved@redhat.com> Acked-by: Jeff Layton <jeff.layton@primarydata.com>
* FS-Cache: fscache_object_is_dead() has wrong logic, kill itDavid Howells2015-04-021-6/+0
| | | | | | | | | | | | | fscache_object_is_dead() returns true only if the object is marked dead and the cache got an I/O error. This should be a logical OR instead. Since two of the callers got split up into handling for separate subcases, expand the other callers and kill the function. This is probably the right thing to do anyway since one of the subcases isn't about the object at all, but rather about the cache. Signed-off-by: David Howells <dhowells@redhat.com> Reviewed-by: Steve Dickson <steved@redhat.com> Acked-by: Jeff Layton <jeff.layton@primarydata.com>
* FS-Cache: When submitting an op, cancel it if the target object is dyingDavid Howells2015-04-021-2/+7
| | | | | | | | | | | | | | When submitting an operation, prefer to cancel the operation immediately rather than queuing it for later processing if the object is marked as dying (ie. the object state machine has reached the KILL_OBJECT state). Whilst we're at it, change the series of related test_bit() calls into a READ_ONCE() and bitwise-AND operators to reduce the number of load instructions (test_bit() has a volatile address). Signed-off-by: David Howells <dhowells@redhat.com> Reviewed-by: Steve Dickson <steved@redhat.com> Acked-by: Jeff Layton <jeff.layton@primarydata.com>
* FS-Cache: Count culled objects and objects rejected due to lack of spaceDavid Howells2015-02-241-0/+12
| | | | | | | | | | | | Count the number of objects that get culled by the cache backend and the number of objects that the cache backend declines to instantiate due to lack of space in the cache. These numbers are made available through /proc/fs/fscache/stats Signed-off-by: David Howells <dhowells@redhat.com> Reviewed-by: Steve Dickson <steved@redhat.com> Acked-by: Jeff Layton <jeff.layton@primarydata.com>
* FS-Cache: Provide the ability to enable/disable cookiesDavid Howells2013-09-271-30/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Provide the ability to enable and disable fscache cookies. A disabled cookie will reject or ignore further requests to: Acquire a child cookie Invalidate and update backing objects Check the consistency of a backing object Allocate storage for backing page Read backing pages Write to backing pages but still allows: Checks/waits on the completion of already in-progress objects Uncaching of pages Relinquishment of cookies Two new operations are provided: (1) Disable a cookie: void fscache_disable_cookie(struct fscache_cookie *cookie, bool invalidate); If the cookie is not already disabled, this locks the cookie against other dis/enablement ops, marks the cookie as being disabled, discards or invalidates any backing objects and waits for cessation of activity on any associated object. This is a wrapper around a chunk split out of fscache_relinquish_cookie(), but it reinitialises the cookie such that it can be reenabled. All possible failures are handled internally. The caller should consider calling fscache_uncache_all_inode_pages() afterwards to make sure all page markings are cleared up. (2) Enable a cookie: void fscache_enable_cookie(struct fscache_cookie *cookie, bool (*can_enable)(void *data), void *data) If the cookie is not already enabled, this locks the cookie against other dis/enablement ops, invokes can_enable() and, if the cookie is not an index cookie, will begin the procedure of acquiring backing objects. The optional can_enable() function is passed the data argument and returns a ruling as to whether or not enablement should actually be permitted to begin. All possible failures are handled internally. The cookie will only be marked as enabled if provisional backing objects are allocated. A later patch will introduce these to NFS. Cookie enablement during nfs_open() is then contingent on i_writecount <= 0. can_enable() checks for a race between open(O_RDONLY) and open(O_WRONLY/O_RDWR). This simplifies NFS's cookie handling and allows us to get rid of open(O_RDONLY) accidentally introducing caching to an inode that's open for writing already. One operation has its API modified: (3) Acquire a cookie. struct fscache_cookie *fscache_acquire_cookie( struct fscache_cookie *parent, const struct fscache_cookie_def *def, void *netfs_data, bool enable); This now has an additional argument that indicates whether the requested cookie should be enabled by default. It doesn't need the can_enable() function because the caller must prevent multiple calls for the same netfs object and it doesn't need to take the enablement lock because no one else can get at the cookie before this returns. Signed-off-by: David Howells <dhowells@redhat.com
* FS-Cache: Add use/unuse/wake cookie wrappersDavid Howells2013-09-271-2/+17
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Add wrapper functions for dealing with cookie->n_active: (*) __fscache_use_cookie() to increment it. (*) __fscache_unuse_cookie() to decrement and test against zero. (*) __fscache_wake_unused_cookie() to wake up anyone waiting for it to reach zero. The second and third are split so that the third can be done after cookie->lock has been released in case the waiter wakes up whilst we're still holding it and tries to get it. We will need to wake-on-zero once the cookie disablement patch is applied because it will then be possible to see n_active become zero without the cookie being relinquished. Also move the cookie usement out of fscache_attr_changed_op() and into fscache_attr_changed() and the operation struct so that cookie disablement will be able to track it. Whilst we're at it, only increment n_active if we're about to do fscache_submit_op() so that we don't have to deal with undoing it if anything earlier fails. Possibly this should be moved into fscache_submit_op() which could look at FSCACHE_OP_UNUSE_COOKIE. Signed-off-by: David Howells <dhowells@redhat.com>
* FS-Cache: Add interface to check consistency of a cached objectDavid Howells2013-09-061-0/+4
| | | | | | | | | | | | | | | | | | | | | | | | Extend the fscache netfs API so that the netfs can ask as to whether a cache object is up to date with respect to its corresponding netfs object: int fscache_check_consistency(struct fscache_cookie *cookie) This will call back to the netfs to check whether the auxiliary data associated with a cookie is correct. It returns 0 if it is and -ESTALE if it isn't; it may also return -ENOMEM and -ERESTARTSYS. The backends now have to implement a mandatory operation pointer: int (*check_consistency)(struct fscache_object *object) that corresponds to the above API call. FS-Cache takes care of pinning the object and the cookie in memory and managing this call with respect to the object state. Original-author: Hongyi Jia <jiayisuse@gmail.com> Signed-off-by: David Howells <dhowells@redhat.com> cc: Hongyi Jia <jiayisuse@gmail.com> cc: Milosz Tanski <milosz@adfin.com>
* FS-Cache: The retrieval remaining-pages counter needs to be atomic_tDavid Howells2013-06-191-4/+3
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | struct fscache_retrieval contains a count of the number of pages that still need some processing (n_pages). This is decremented as the pages are processed. However, this needs to be atomic as fscache_retrieval_complete() (I think) just occasionally may be called from cachefiles_read_backing_file() and cachefiles_read_copier() simultaneously. This happens when an fscache_read_or_alloc_pages() request containing a lot of pages (say a couple of hundred) is being processed. The read on each backing page is dispatched individually because we need to insert a monitor into the waitqueue to catch when the read completes. However, under low-memory conditions, we might be forced to wait in the allocator - and this gives the I/O on the backing page a chance to complete first. When the I/O completes, fscache_enqueue_retrieval() chucks the retrieval onto the workqueue without waiting for the operation to finish the initial I/O dispatch (we want to release any pages we can as soon as we can), thus both can end up running simultaneously and potentially attempting to partially complete the retrieval simultaneously (ENOMEM may occur, backing pages may already be in the page cache). This was demonstrated by parallelling the non-atomic counter with an atomic counter and printing both of them when the assertion fails. At this point, the atomic counter has reached zero, but the non-atomic counter has not. To fix this, make the counter an atomic_t. This results in the following bug appearing FS-Cache: Assertion failed 3 == 5 is false ------------[ cut here ]------------ kernel BUG at fs/fscache/operation.c:421! or FS-Cache: Assertion failed 3 == 5 is false ------------[ cut here ]------------ kernel BUG at fs/fscache/operation.c:414! With a backtrace like the following: RIP: 0010:[<ffffffffa0211b1d>] fscache_put_operation+0x1ad/0x240 [fscache] Call Trace: [<ffffffffa0213185>] fscache_retrieval_work+0x55/0x270 [fscache] [<ffffffffa0213130>] ? fscache_retrieval_work+0x0/0x270 [fscache] [<ffffffff81090b10>] worker_thread+0x170/0x2a0 [<ffffffff81096d10>] ? autoremove_wake_function+0x0/0x40 [<ffffffff810909a0>] ? worker_thread+0x0/0x2a0 [<ffffffff81096966>] kthread+0x96/0xa0 [<ffffffff8100c0ca>] child_rip+0xa/0x20 [<ffffffff810968d0>] ? kthread+0x0/0xa0 [<ffffffff8100c0c0>] ? child_rip+0x0/0x20 Signed-off-by: David Howells <dhowells@redhat.com> Reviewed-and-tested-By: Milosz Tanski <milosz@adfin.com> Acked-by: Jeff Layton <jlayton@redhat.com>
* FS-Cache: Simplify cookie retention for fscache_objects, fixing oopsDavid Howells2013-06-191-16/+39
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Simplify the way fscache cache objects retain their cookie. The way I implemented the cookie storage handling made synchronisation a pain (ie. the object state machine can't rely on the cookie actually still being there). Instead of the the object being detached from the cookie and the cookie being freed in __fscache_relinquish_cookie(), we defer both operations: (*) The detachment of the object from the list in the cookie now takes place in fscache_drop_object() and is thus governed by the object state machine (fscache_detach_from_cookie() has been removed). (*) The release of the cookie is now in fscache_object_destroy() - which is called by the cache backend just before it frees the object. This means that the fscache_cookie struct is now available to the cache all the way through from ->alloc_object() to ->drop_object() and ->put_object() - meaning that it's no longer necessary to take object->lock to guarantee access. However, __fscache_relinquish_cookie() doesn't wait for the object to go all the way through to destruction before letting the netfs proceed. That would massively slow down the netfs. Since __fscache_relinquish_cookie() leaves the cookie around, in must therefore break all attachments to the netfs - which includes ->def, ->netfs_data and any outstanding page read/writes. To handle this, struct fscache_cookie now has an n_active counter: (1) This starts off initialised to 1. (2) Any time the cache needs to get at the netfs data, it calls fscache_use_cookie() to increment it - if it is not zero. If it was zero, then access is not permitted. (3) When the cache has finished with the data, it calls fscache_unuse_cookie() to decrement it. This does a wake-up on it if it reaches 0. (4) __fscache_relinquish_cookie() decrements n_active and then waits for it to reach 0. The initialisation to 1 in step (1) ensures that we only get wake ups when we're trying to get rid of the cookie. This leaves __fscache_relinquish_cookie() a lot simpler. *** This fixes a problem in the current code whereby if fscache_invalidate() is followed sufficiently quickly by fscache_relinquish_cookie() then it is possible for __fscache_relinquish_cookie() to have detached the cookie from the object and cleared the pointer before a thread is dispatched to process the invalidation state in the object state machine. Since the pending write clearance was deferred to the invalidation state to make it asynchronous, we need to either wait in relinquishment for the stores tree to be cleared in the invalidation state or we need to handle the clearance in relinquishment. Further, if the relinquishment code does clear the tree, then the invalidation state need to make the clearance contingent on still having the cookie to hand (since that's where the tree is rooted) and we have to prevent the cookie from disappearing for the duration. This can lead to an oops like the following: BUG: unable to handle kernel NULL pointer dereference at 000000000000000c ... RIP: 0010:[<ffffffff8151023e>] _spin_lock+0xe/0x30 ... CR2: 000000000000000c ... ... Process kslowd002 (...) .... Call Trace: [<ffffffffa01c3278>] fscache_invalidate_writes+0x38/0xd0 [fscache] [<ffffffff810096f0>] ? __switch_to+0xd0/0x320 [<ffffffff8105e759>] ? find_busiest_queue+0x69/0x150 [<ffffffff8110ddd4>] ? slow_work_enqueue+0x104/0x180 [<ffffffffa01c1303>] fscache_object_slow_work_execute+0x5e3/0x9d0 [fscache] [<ffffffff81096b67>] ? bit_waitqueue+0x17/0xd0 [<ffffffff8110e233>] slow_work_execute+0x233/0x310 [<ffffffff8110e515>] slow_work_thread+0x205/0x360 [<ffffffff81096ca0>] ? autoremove_wake_function+0x0/0x40 [<ffffffff8110e310>] ? slow_work_thread+0x0/0x360 [<ffffffff81096936>] kthread+0x96/0xa0 [<ffffffff8100c0ca>] child_rip+0xa/0x20 [<ffffffff810968a0>] ? kthread+0x0/0xa0 [<ffffffff8100c0c0>] ? child_rip+0x0/0x20 The parameter to fscache_invalidate_writes() was object->cookie which is NULL. Signed-off-by: David Howells <dhowells@redhat.com> Tested-By: Milosz Tanski <milosz@adfin.com> Acked-by: Jeff Layton <jlayton@redhat.com>
* FS-Cache: Fix object state machine to have separate work and wait statesDavid Howells2013-06-191-35/+31
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Fix object state machine to have separate work and wait states as that makes it easier to envision. There are now three kinds of state: (1) Work state. This is an execution state. No event processing is performed by a work state. The function attached to a work state returns a pointer indicating the next state to which the OSM should transition. Returning NO_TRANSIT repeats the current state, but goes back to the scheduler first. (2) Wait state. This is an event processing state. No execution is performed by a wait state. Wait states are just tables of "if event X occurs, clear it and transition to state Y". The dispatcher returns to the scheduler if none of the events in which the wait state has an interest are currently pending. (3) Out-of-band state. This is a special work state. Transitions to normal states can be overridden when an unexpected event occurs (eg. I/O error). Instead the dispatcher disables and clears the OOB event and transits to the specified work state. This then acts as an ordinary work state, though object->state points to the overridden destination. Returning NO_TRANSIT resumes the overridden transition. In addition, the states have names in their definitions, so there's no need for tables of state names. Further, the EV_REQUEUE event is no longer necessary as that is automatic for work states. Since the states are now separate structs rather than values in an enum, it's not possible to use comparisons other than (non-)equality between them, so use some object->flags to indicate what phase an object is in. The EV_RELEASE, EV_RETIRE and EV_WITHDRAW events have been squished into one (EV_KILL). An object flag now carries the information about retirement. Similarly, the RELEASING, RECYCLING and WITHDRAWING states have been merged into an KILL_OBJECT state and additional states have been added for handling waiting dependent objects (JUMPSTART_DEPS and KILL_DEPENDENTS). A state has also been added for synchronising with parent object initialisation (WAIT_FOR_PARENT) and another for initiating look up (PARENT_READY). Signed-off-by: David Howells <dhowells@redhat.com> Tested-By: Milosz Tanski <milosz@adfin.com> Acked-by: Jeff Layton <jlayton@redhat.com>
* FS-Cache: Wrap checks on object stateDavid Howells2013-06-191-9/+28
| | | | | | | | | | | | Wrap checks on object state (mostly outside of fs/fscache/object.c) with inline functions so that the mechanism can be replaced. Some of the state checks within object.c are left as-is as they will be replaced. Signed-off-by: David Howells <dhowells@redhat.com> Tested-By: Milosz Tanski <milosz@adfin.com> Acked-by: Jeff Layton <jlayton@redhat.com>
* FS-Cache: Uninline fscache_object_init()David Howells2013-06-191-36/+2
| | | | | | | | | Uninline fscache_object_init() so as not to expose some of the FS-Cache internals to the cache backend. Signed-off-by: David Howells <dhowells@redhat.com> Tested-By: Milosz Tanski <milosz@adfin.com> Acked-by: Jeff Layton <jlayton@redhat.com>
* FS-Cache: Mark cancellation of in-progress operationDavid Howells2012-12-201-2/+2
| | | | | | | | Mark as cancelled an operation that is in progress rather than pending at the time it is cancelled, and call fscache_complete_op() to cancel an operation so that blocked ops can be started. Signed-off-by: David Howells <dhowells@redhat.com>
* FS-Cache: Convert the object event ID #defines into an enumDavid Howells2012-12-201-9/+17
| | | | | | | | Convert the fscache_object event IDs from #defines into an enum. Also add an extra label to the enum to carry the event count and redefine the event mask in terms of that. Signed-off-by: David Howells <dhowells@redhat.com>
* FS-Cache: Provide proper invalidationDavid Howells2012-12-201-1/+7
| | | | | | | | | | | | | | | Provide a proper invalidation method rather than relying on the netfs retiring the cookie it has and getting a new one. The problem with this is that isn't easy for the netfs to make sure that it has completed/cancelled all its outstanding storage and retrieval operations on the cookie it is retiring. Instead, have the cache provide an invalidation method that will cancel or wait for all currently outstanding operations before invalidating the cache, and will cause new operations to queue up behind that. Whilst invalidation is in progress, some requests will be rejected until the cache can stack a barrier on the operation queue to cause new operations to be deferred behind it. Signed-off-by: David Howells <dhowells@redhat.com>
* FS-Cache: Fix operation state management and accountingDavid Howells2012-12-201-5/+32
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Fix the state management of internal fscache operations and the accounting of what operations are in what states. This is done by: (1) Give struct fscache_operation a enum variable that directly represents the state it's currently in, rather than spreading this knowledge over a bunch of flags, who's processing the operation at the moment and whether it is queued or not. This makes it easier to write assertions to check the state at various points and to prevent invalid state transitions. (2) Add an 'operation complete' state and supply a function to indicate the completion of an operation (fscache_op_complete()) and make things call it. The final call to fscache_put_operation() can then check that an op in the appropriate state (complete or cancelled). (3) Adjust the use of object->n_ops, ->n_in_progress, ->n_exclusive to better govern the state of an object: (a) The ->n_ops is now the number of extant operations on the object and is now decremented by fscache_put_operation() only. (b) The ->n_in_progress is simply the number of objects that have been taken off of the object's pending queue for the purposes of being run. This is decremented by fscache_op_complete() only. (c) The ->n_exclusive is the number of exclusive ops that have been submitted and queued or are in progress. It is decremented by fscache_op_complete() and by fscache_cancel_op(). fscache_put_operation() and fscache_operation_gc() now no longer try to clean up ->n_exclusive and ->n_in_progress. That was leading to double decrements against fscache_cancel_op(). fscache_cancel_op() now no longer decrements ->n_ops. That was leading to double decrements against fscache_put_operation(). fscache_submit_exclusive_op() now decides whether it has to queue an op based on ->n_in_progress being > 0 rather than ->n_ops > 0 as the latter will persist in being true even after all preceding operations have been cancelled or completed. Furthermore, if an object is active and there are runnable ops against it, there must be at least one op running. (4) Add a remaining-pages counter (n_pages) to struct fscache_retrieval and provide a function to record completion of the pages as they complete. When n_pages reaches 0, the operation is deemed to be complete and fscache_op_complete() is called. Add calls to fscache_retrieval_complete() anywhere we've finished with a page we've been given to read or allocate for. This includes places where we just return pages to the netfs for reading from the server and where accessing the cache fails and we discard the proposed netfs page. The bugs in the unfixed state management manifest themselves as oopses like the following where the operation completion gets out of sync with return of the cookie by the netfs. This is possible because the cache unlocks and returns all the netfs pages before recording its completion - which means that there's nothing to stop the netfs discarding them and returning the cookie. FS-Cache: Cookie 'NFS.fh' still has outstanding reads ------------[ cut here ]------------ kernel BUG at fs/fscache/cookie.c:519! invalid opcode: 0000 [#1] SMP CPU 1 Modules linked in: cachefiles nfs fscache auth_rpcgss nfs_acl lockd sunrpc Pid: 400, comm: kswapd0 Not tainted 3.1.0-rc7-fsdevel+ #1090 /DG965RY RIP: 0010:[<ffffffffa007050a>] [<ffffffffa007050a>] __fscache_relinquish_cookie+0x170/0x343 [fscache] RSP: 0018:ffff8800368cfb00 EFLAGS: 00010282 RAX: 000000000000003c RBX: ffff880023cc8790 RCX: 0000000000000000 RDX: 0000000000002f2e RSI: 0000000000000001 RDI: ffffffff813ab86c RBP: ffff8800368cfb50 R08: 0000000000000002 R09: 0000000000000000 R10: ffff88003a1b7890 R11: ffff88001df6e488 R12: ffff880023d8ed98 R13: ffff880023cc8798 R14: 0000000000000004 R15: ffff88003b8bf370 FS: 0000000000000000(0000) GS:ffff88003bd00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b CR2: 00000000008ba008 CR3: 0000000023d93000 CR4: 00000000000006e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 Process kswapd0 (pid: 400, threadinfo ffff8800368ce000, task ffff88003b8bf040) Stack: ffff88003b8bf040 ffff88001df6e528 ffff88001df6e528 ffffffffa00b46b0 ffff88003b8bf040 ffff88001df6e488 ffff88001df6e620 ffffffffa00b46b0 ffff88001ebd04c8 0000000000000004 ffff8800368cfb70 ffffffffa00b2c91 Call Trace: [<ffffffffa00b2c91>] nfs_fscache_release_inode_cookie+0x3b/0x47 [nfs] [<ffffffffa008f25f>] nfs_clear_inode+0x3c/0x41 [nfs] [<ffffffffa0090df1>] nfs4_evict_inode+0x2f/0x33 [nfs] [<ffffffff810d8d47>] evict+0xa1/0x15c [<ffffffff810d8e2e>] dispose_list+0x2c/0x38 [<ffffffff810d9ebd>] prune_icache_sb+0x28c/0x29b [<ffffffff810c56b7>] prune_super+0xd5/0x140 [<ffffffff8109b615>] shrink_slab+0x102/0x1ab [<ffffffff8109d690>] balance_pgdat+0x2f2/0x595 [<ffffffff8103e009>] ? process_timeout+0xb/0xb [<ffffffff8109dba3>] kswapd+0x270/0x289 [<ffffffff8104c5ea>] ? __init_waitqueue_head+0x46/0x46 [<ffffffff8109d933>] ? balance_pgdat+0x595/0x595 [<ffffffff8104bf7a>] kthread+0x7f/0x87 [<ffffffff813ad6b4>] kernel_thread_helper+0x4/0x10 [<ffffffff81026b98>] ? finish_task_switch+0x45/0xc0 [<ffffffff813abcdd>] ? retint_restore_args+0xe/0xe [<ffffffff8104befb>] ? __init_kthread_worker+0x53/0x53 [<ffffffff813ad6b0>] ? gs_change+0xb/0xb Signed-off-by: David Howells <dhowells@redhat.com>
* FS-Cache: Make cookie relinquishment wait for outstanding readsDavid Howells2012-12-201-0/+1
| | | | | | | Make fscache_relinquish_cookie() log a warning and wait if there are any outstanding reads left on the cookie it was given. Signed-off-by: David Howells <dhowells@redhat.com>
* CacheFiles: Fix the marking of cached pagesDavid Howells2012-12-201-0/+3
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Under some circumstances CacheFiles defers the marking of pages with PG_fscache so that it can take advantage of pagevecs to reduce the number of calls to fscache_mark_pages_cached() and the netfs's hook to keep track of this. There are, however, two problems with this: (1) It can lead to the PG_fscache mark being applied _after_ the page is set PG_uptodate and unlocked (by the call to fscache_end_io()). (2) CacheFiles's ref on the page is dropped immediately following fscache_end_io() - and so may not still be held when the mark is applied. This can lead to the page being passed back to the allocator before the mark is applied. Fix this by, where appropriate, marking the page before calling fscache_end_io() and releasing the page. This means that we can't take advantage of pagevecs and have to make a separate call for each page to the marking routines. The symptoms of this are Bad Page state errors cropping up under memory pressure, for example: BUG: Bad page state in process tar pfn:002da page:ffffea0000009fb0 count:0 mapcount:0 mapping: (null) index:0x1447 page flags: 0x1000(private_2) Pid: 4574, comm: tar Tainted: G W 3.1.0-rc4-fsdevel+ #1064 Call Trace: [<ffffffff8109583c>] ? dump_page+0xb9/0xbe [<ffffffff81095916>] bad_page+0xd5/0xea [<ffffffff81095d82>] get_page_from_freelist+0x35b/0x46a [<ffffffff810961f3>] __alloc_pages_nodemask+0x362/0x662 [<ffffffff810989da>] __do_page_cache_readahead+0x13a/0x267 [<ffffffff81098942>] ? __do_page_cache_readahead+0xa2/0x267 [<ffffffff81098d7b>] ra_submit+0x1c/0x20 [<ffffffff8109900a>] ondemand_readahead+0x28b/0x29a [<ffffffff81098ee2>] ? ondemand_readahead+0x163/0x29a [<ffffffff810990ce>] page_cache_sync_readahead+0x38/0x3a [<ffffffff81091d8a>] generic_file_aio_read+0x2ab/0x67e [<ffffffffa008cfbe>] nfs_file_read+0xa4/0xc9 [nfs] [<ffffffff810c22c4>] do_sync_read+0xba/0xfa [<ffffffff81177a47>] ? security_file_permission+0x7b/0x84 [<ffffffff810c25dd>] ? rw_verify_area+0xab/0xc8 [<ffffffff810c29a4>] vfs_read+0xaa/0x13a [<ffffffff810c2a79>] sys_read+0x45/0x6c [<ffffffff813ac37b>] system_call_fastpath+0x16/0x1b As can be seen, PG_private_2 (== PG_fscache) is set in the page flags. Instrumenting fscache_mark_pages_cached() to verify whether page->mapping was set appropriately showed that sometimes it wasn't. This led to the discovery that sometimes the page has apparently been reclaimed by the time the marker got to see it. Reported-by: M. Stevens <m@tippett.com> Signed-off-by: David Howells <dhowells@redhat.com> Reviewed-by: Jeff Layton <jlayton@redhat.com>
* treewide: use __printf not __attribute__((format(printf,...)))Joe Perches2011-10-311-4/+4
| | | | | | | | | | | | | | | | | Standardize the style for compiler based printf format verification. Standardized the location of __printf too. Done via script and a little typing. $ grep -rPl --include=*.[ch] -w "__attribute__" * | \ grep -vP "^(tools|scripts|include/linux/compiler-gcc.h)" | \ xargs perl -n -i -e 'local $/; while (<>) { s/\b__attribute__\s*\(\s*\(\s*format\s*\(\s*printf\s*,\s*(.+)\s*,\s*(.+)\s*\)\s*\)\s*\)/__printf($1, $2)/g ; print; }' [akpm@linux-foundation.org: revert arch bits] Signed-off-by: Joe Perches <joe@perches.com> Cc: "Kirill A. Shutemov" <kirill@shutemov.name> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* fscache: remove dead code under CONFIG_WORKQUEUE_DEBUGFSAmerigo Wang2011-05-251-12/+0
| | | | | | | | | There is no CONFIG_WORKQUEUE_DEBUGFS any more, so this code is dead. Signed-off-by: WANG Cong <amwang@redhat.com> Cc: David Howells <dhowells@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* Fix common misspellingsLucas De Marchi2011-03-311-1/+1
| | | | | | Fixes generated by 'codespell' and manually reviewed. Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
* fscache: drop references to slow-workTejun Heo2010-07-221-1/+0
| | | | | | | fscache no longer uses slow-work. Drop references to it. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: David Howells <dhowells@redhat.com>
* fscache: convert operation to use workqueue instead of slow-workTejun Heo2010-07-221-26/+11
| | | | | | | | | | | | | | | | | | | | | | | | Make fscache operation to use only workqueue instead of combination of workqueue and slow-work. FSCACHE_OP_SLOW is dropped and FSCACHE_OP_FAST is renamed to FSCACHE_OP_ASYNC and uses newly added fscache_op_wq workqueue to execute op->processor(). fscache_operation_init_slow() is dropped and fscache_operation_init() now takes @processor argument directly. * Unbound workqueue is used. * fscache_retrieval_work() is no longer necessary as OP_ASYNC now does the equivalent thing. * sysctl fscache.operation_max_active added to control concurrency. The default value is nr_cpus clamped between 2 and WQ_UNBOUND_MAX_ACTIVE. * debugfs support is dropped for now. Tracing API based debug facility is planned to be added. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: David Howells <dhowells@redhat.com>
* fscache: convert object to use workqueue instead of slow-workTejun Heo2010-07-221-3/+6
| | | | | | | | | | | | | | | | | | | | | | | | | | | | Make fscache object state transition callbacks use workqueue instead of slow-work. New dedicated unbound CPU workqueue fscache_object_wq is created. get/put callbacks are renamed and modified to take @object and called directly from the enqueue wrapper and the work function. While at it, make all open coded instances of get/put to use fscache_get/put_object(). * Unbound workqueue is used. * work_busy() output is printed instead of slow-work flags in object debugging outputs. They mean basically the same thing bit-for-bit. * sysctl fscache.object_max_active added to control concurrency. The default value is nr_cpus clamped between 4 and WQ_UNBOUND_MAX_ACTIVE. * slow_work_sleep_till_thread_needed() is replaced with fscache private implementation fscache_object_sleep_till_congested() which waits on fscache_object_wq congestion. * debugfs support is dropped for now. Tracing API based debug facility is planned to be added. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: David Howells <dhowells@redhat.com>
* SLOW_WORK: CONFIG_SLOW_WORK_PROC should be CONFIG_SLOW_WORK_DEBUGDavid Howells2010-03-291-1/+1
| | | | | | | | | CONFIG_SLOW_WORK_PROC was changed to CONFIG_SLOW_WORK_DEBUG, but not in all instances. Change the remaining instances. This makes the debugfs file display the time mark and the owner's description again. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* CacheFiles: Catch an overly long wait for an old active objectDavid Howells2009-11-191-2/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Catch an overly long wait for an old, dying active object when we want to replace it with a new one. The probability is that all the slow-work threads are hogged, and the delete can't get a look in. What we do instead is: (1) if there's nothing in the slow work queue, we sleep until either the dying object has finished dying or there is something in the slow work queue behind which we can queue our object. (2) if there is something in the slow work queue, we return ETIMEDOUT to fscache_lookup_object(), which then puts us back on the slow work queue, presumably behind the deletion that we're blocked by. We are then deferred for a while until we work our way back through the queue - without blocking a slow-work thread unnecessarily. A backtrace similar to the following may appear in the log without this patch: INFO: task kslowd004:5711 blocked for more than 120 seconds. "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. kslowd004 D 0000000000000000 0 5711 2 0x00000080 ffff88000340bb80 0000000000000046 ffff88002550d000 0000000000000000 ffff88002550d000 0000000000000007 ffff88000340bfd8 ffff88002550d2a8 000000000000ddf0 00000000000118c0 00000000000118c0 ffff88002550d2a8 Call Trace: [<ffffffff81058e21>] ? trace_hardirqs_on+0xd/0xf [<ffffffffa011c4d8>] ? cachefiles_wait_bit+0x0/0xd [cachefiles] [<ffffffffa011c4e1>] cachefiles_wait_bit+0x9/0xd [cachefiles] [<ffffffff81353153>] __wait_on_bit+0x43/0x76 [<ffffffff8111ae39>] ? ext3_xattr_get+0x1ec/0x270 [<ffffffff813531ef>] out_of_line_wait_on_bit+0x69/0x74 [<ffffffffa011c4d8>] ? cachefiles_wait_bit+0x0/0xd [cachefiles] [<ffffffff8104c125>] ? wake_bit_function+0x0/0x2e [<ffffffffa011bc79>] cachefiles_mark_object_active+0x203/0x23b [cachefiles] [<ffffffffa011c209>] cachefiles_walk_to_object+0x558/0x827 [cachefiles] [<ffffffffa011a429>] cachefiles_lookup_object+0xac/0x12a [cachefiles] [<ffffffffa00aa1e9>] fscache_lookup_object+0x1c7/0x214 [fscache] [<ffffffffa00aafc5>] fscache_object_state_machine+0xa5/0x52d [fscache] [<ffffffffa00ab4ac>] fscache_object_slow_work_execute+0x5f/0xa0 [fscache] [<ffffffff81082093>] slow_work_execute+0x18f/0x2d1 [<ffffffff8108239a>] slow_work_thread+0x1c5/0x308 [<ffffffff8104c0f1>] ? autoremove_wake_function+0x0/0x34 [<ffffffff810821d5>] ? slow_work_thread+0x0/0x308 [<ffffffff8104be91>] kthread+0x7a/0x82 [<ffffffff8100beda>] child_rip+0xa/0x20 [<ffffffff8100b87c>] ? restore_args+0x0/0x30 [<ffffffff8104be17>] ? kthread+0x0/0x82 [<ffffffff8100bed0>] ? child_rip+0x0/0x20 1 lock held by kslowd004/5711: #0: (&sb->s_type->i_mutex_key#7/1){+.+.+.}, at: [<ffffffffa011be64>] cachefiles_walk_to_object+0x1b3/0x827 [cachefiles] Signed-off-by: David Howells <dhowells@redhat.com>
* CacheFiles: Don't write a full page if there's only a partial page to cacheDavid Howells2009-11-191-0/+3
| | | | | | | | | | | | | | | | | | | | | | | | cachefiles_write_page() writes a full page to the backing file for the last page of the netfs file, even if the netfs file's last page is only a partial page. This causes the EOF on the backing file to be extended beyond the EOF of the netfs, and thus the backing file will be truncated by cachefiles_attr_changed() called from cachefiles_lookup_object(). So we need to limit the write we make to the backing file on that last page such that it doesn't push the EOF too far. Also, if a backing file that has a partial page at the end is expanded, we discard the partial page and refetch it on the basis that we then have a hole in the file with invalid data, and should the power go out... A better way to deal with this could be to record a note that the partial page contains invalid data until the correct data is written into it. This isn't a problem for netfs's that discard the whole backing file if the file size changes (such as NFS). Signed-off-by: David Howells <dhowells@redhat.com>
* FS-Cache: Start processing an object's operations on that object's deathDavid Howells2009-11-191-0/+4
| | | | | | | | | | | | | | | | Start processing an object's operations when that object moves into the DYING state as the object cannot be destroyed until all its outstanding operations have completed. Furthermore, make sure that read and allocation operations handle being woken up on a dead object. Such events are recorded in the Allocs.abt and Retrvls.abt statistics as viewable through /proc/fs/fscache/stats. The code for waiting for object activation for the read and allocation operations is also extracted into its own function as it is much the same in all cases, differing only in the stats incremented. Signed-off-by: David Howells <dhowells@redhat.com>
* FS-Cache: Handle pages pending storage that get evicted under OOM conditionsDavid Howells2009-11-191-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Handle netfs pages that the vmscan algorithm wants to evict from the pagecache under OOM conditions, but that are waiting for write to the cache. Under these conditions, vmscan calls the releasepage() function of the netfs, asking if a page can be discarded. The problem is typified by the following trace of a stuck process: kslowd005 D 0000000000000000 0 4253 2 0x00000080 ffff88001b14f370 0000000000000046 ffff880020d0d000 0000000000000007 0000000000000006 0000000000000001 ffff88001b14ffd8 ffff880020d0d2a8 000000000000ddf0 00000000000118c0 00000000000118c0 ffff880020d0d2a8 Call Trace: [<ffffffffa00782d8>] __fscache_wait_on_page_write+0x8b/0xa7 [fscache] [<ffffffff8104c0f1>] ? autoremove_wake_function+0x0/0x34 [<ffffffffa0078240>] ? __fscache_check_page_write+0x63/0x70 [fscache] [<ffffffffa00b671d>] nfs_fscache_release_page+0x4e/0xc4 [nfs] [<ffffffffa00927f0>] nfs_release_page+0x3c/0x41 [nfs] [<ffffffff810885d3>] try_to_release_page+0x32/0x3b [<ffffffff81093203>] shrink_page_list+0x316/0x4ac [<ffffffff8109372b>] shrink_inactive_list+0x392/0x67c [<ffffffff813532fa>] ? __mutex_unlock_slowpath+0x100/0x10b [<ffffffff81058df0>] ? trace_hardirqs_on_caller+0x10c/0x130 [<ffffffff8135330e>] ? mutex_unlock+0x9/0xb [<ffffffff81093aa2>] shrink_list+0x8d/0x8f [<ffffffff81093d1c>] shrink_zone+0x278/0x33c [<ffffffff81052d6c>] ? ktime_get_ts+0xad/0xba [<ffffffff81094b13>] try_to_free_pages+0x22e/0x392 [<ffffffff81091e24>] ? isolate_pages_global+0x0/0x212 [<ffffffff8108e743>] __alloc_pages_nodemask+0x3dc/0x5cf [<ffffffff81089529>] grab_cache_page_write_begin+0x65/0xaa [<ffffffff8110f8c0>] ext3_write_begin+0x78/0x1eb [<ffffffff81089ec5>] generic_file_buffered_write+0x109/0x28c [<ffffffff8103cb69>] ? current_fs_time+0x22/0x29 [<ffffffff8108a509>] __generic_file_aio_write+0x350/0x385 [<ffffffff8108a588>] ? generic_file_aio_write+0x4a/0xae [<ffffffff8108a59e>] generic_file_aio_write+0x60/0xae [<ffffffff810b2e82>] do_sync_write+0xe3/0x120 [<ffffffff8104c0f1>] ? autoremove_wake_function+0x0/0x34 [<ffffffff810b18e1>] ? __dentry_open+0x1a5/0x2b8 [<ffffffff810b1a76>] ? dentry_open+0x82/0x89 [<ffffffffa00e693c>] cachefiles_write_page+0x298/0x335 [cachefiles] [<ffffffffa0077147>] fscache_write_op+0x178/0x2c2 [fscache] [<ffffffffa0075656>] fscache_op_execute+0x7a/0xd1 [fscache] [<ffffffff81082093>] slow_work_execute+0x18f/0x2d1 [<ffffffff8108239a>] slow_work_thread+0x1c5/0x308 [<ffffffff8104c0f1>] ? autoremove_wake_function+0x0/0x34 [<ffffffff810821d5>] ? slow_work_thread+0x0/0x308 [<ffffffff8104be91>] kthread+0x7a/0x82 [<ffffffff8100beda>] child_rip+0xa/0x20 [<ffffffff8100b87c>] ? restore_args+0x0/0x30 [<ffffffff8102ef83>] ? tg_shares_up+0x171/0x227 [<ffffffff8104be17>] ? kthread+0x0/0x82 [<ffffffff8100bed0>] ? child_rip+0x0/0x20 In the above backtrace, the following is happening: (1) A page storage operation is being executed by a slow-work thread (fscache_write_op()). (2) FS-Cache farms the operation out to the cache to perform (cachefiles_write_page()). (3) CacheFiles is then calling Ext3 to perform the actual write, using Ext3's standard write (do_sync_write()) under KERNEL_DS directly from the netfs page. (4) However, for Ext3 to perform the write, it must allocate some memory, in particular, it must allocate at least one page cache page into which it can copy the data from the netfs page. (5) Under OOM conditions, the memory allocator can't immediately come up with a page, so it uses vmscan to find something to discard (try_to_free_pages()). (6) vmscan finds a clean netfs page it might be able to discard (possibly the one it's trying to write out). (7) The netfs is called to throw the page away (nfs_release_page()) - but it's called with __GFP_WAIT, so the netfs decides to wait for the store to complete (__fscache_wait_on_page_write()). (8) This blocks a slow-work processing thread - possibly against itself. The system ends up stuck because it can't write out any netfs pages to the cache without allocating more memory. To avoid this, we make FS-Cache cancel some writes that aren't in the middle of actually being performed. This means that some data won't make it into the cache this time. To support this, a new FS-Cache function is added fscache_maybe_release_page() that replaces what the netfs releasepage() functions used to do with respect to the cache. The decisions fscache_maybe_release_page() makes are counted and displayed through /proc/fs/fscache/stats on a line labelled "VmScan". There are four counters provided: "nos=N" - pages that weren't pending storage; "gon=N" - pages that were pending storage when we first looked, but weren't by the time we got the object lock; "bsy=N" - pages that we ignored as they were actively being written when we looked; and "can=N" - pages that we cancelled the storage of. What I'd really like to do is alter the behaviour of the cancellation heuristics, depending on how necessary it is to expel pages. If there are plenty of other pages that aren't waiting to be written to the cache that could be ejected first, then it would be nice to hold up on immediate cancellation of cache writes - but I don't see a way of doing that. Signed-off-by: David Howells <dhowells@redhat.com>
* FS-Cache: Fix lock misorder in fscache_write_op()David Howells2009-11-191-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | FS-Cache has two structs internally for keeping track of the internal state of a cached file: the fscache_cookie struct, which represents the netfs's state, and fscache_object struct, which represents the cache's state. Each has a pointer that points to the other (when both are in existence), and each has a spinlock for pointer maintenance. Since netfs operations approach these structures from the cookie side, they get the cookie lock first, then the object lock. Cache operations, on the other hand, approach from the object side, and get the object lock first. It is not then permitted for a cache operation to get the cookie lock whilst it is holding the object lock lest deadlock occur; instead, it must do one of two things: (1) increment the cookie usage counter, drop the object lock and then get both locks in order, or (2) simply hold the object lock as certain parts of the cookie may not be altered whilst the object lock is held. It is also not permitted to follow either pointer without holding the lock at the end you start with. To break the pointers between the cookie and the object, both locks must be held. fscache_write_op(), however, violates the locking rules: It attempts to get the cookie lock without (a) checking that the cookie pointer is a valid pointer, and (b) holding the object lock to protect the cookie pointer whilst it follows it. This is so that it can access the pending page store tree without interference from __fscache_write_page(). This is fixed by splitting the cookie lock, such that the page store tracking tree is protected by its own lock, and checking that the cookie pointer is non-NULL before we attempt to follow it whilst holding the object lock. The new lock is subordinate to both the cookie lock and the object lock, and so should be taken after those. Signed-off-by: David Howells <dhowells@redhat.com>
* FS-Cache: Allow the current state of all objects to be dumpedDavid Howells2009-11-191-0/+13
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Allow the current state of all fscache objects to be dumped by doing: cat /proc/fs/fscache/objects By default, all objects and all fields will be shown. This can be restricted by adding a suitable key to one of the caller's keyrings (such as the session keyring): keyctl add user fscache:objlist "<restrictions>" @s The <restrictions> are: K Show hexdump of object key (don't show if not given) A Show hexdump of object aux data (don't show if not given) And paired restrictions: C Show objects that have a cookie c Show objects that don't have a cookie B Show objects that are busy b Show objects that aren't busy W Show objects that have pending writes w Show objects that don't have pending writes R Show objects that have outstanding reads r Show objects that don't have outstanding reads S Show objects that have slow work queued s Show objects that don't have slow work queued If neither side of a restriction pair is given, then both are implied. For example: keyctl add user fscache:objlist KB @s shows objects that are busy, and lists their object keys, but does not dump their auxiliary data. It also implies "CcWwRrSs", but as 'B' is given, 'b' is not implied. Signed-off-by: David Howells <dhowells@redhat.com>
* FS-Cache: Annotate slow-work runqueue proc lines for FS-Cache work itemsDavid Howells2009-11-191-0/+12
| | | | | | | | Annotate slow-work runqueue proc lines for FS-Cache work items. Objects include the object ID and the state. Operations include the object ID, the operation ID and the operation type and state. Signed-off-by: David Howells <dhowells@redhat.com>
* FS-Cache: Add use of /proc and presentation of statisticsDavid Howells2009-04-031-4/+0
| | | | | | | | | | | | | | | | | | | | | | | | | | | Make FS-Cache create its /proc interface and present various statistical information through it. Also provide the functions for updating this information. These features are enabled by: CONFIG_FSCACHE_PROC CONFIG_FSCACHE_STATS CONFIG_FSCACHE_HISTOGRAM The /proc directory for FS-Cache is also exported so that caching modules can add their own statistics there too. The FS-Cache module is loadable at this point, and the statistics files can be examined by userspace: cat /proc/fs/fscache/stats cat /proc/fs/fscache/histogram Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Steve Dickson <steved@redhat.com> Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Tested-by: Daire Byrne <Daire.Byrne@framestore.com>
* FS-Cache: Add the FS-Cache cache backend API and documentationDavid Howells2009-04-031-0/+509
Add the API for a generic facility (FS-Cache) by which caches may declare them selves open for business, and may obtain work to be done from network filesystems. The header file is included by: #include <linux/fscache-cache.h> Documentation for the API is also added to: Documentation/filesystems/caching/backend-api.txt This API is not usable without the implementation of the utility functions which will be added in further patches. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Steve Dickson <steved@redhat.com> Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Tested-by: Daire Byrne <Daire.Byrne@framestore.com>
generated by cgit v1.2.3 (git 2.25.1) at 2024-10-31 11:43:52 +0000