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2022-05-16btrfs: simplify WQ_HIGHPRI handling in struct btrfs_workqueueChristoph Hellwig1-100/+22
Just let the one caller that wants optional WQ_HIGHPRI handling allocate a separate btrfs_workqueue for that. This allows to rename struct __btrfs_workqueue to btrfs_workqueue, remove a pointer indirection and separate allocation for all btrfs_workqueue users and generally simplify the code. Reviewed-by: Qu Wenruo <wqu@suse.com> Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2021-11-16btrfs: fix memory ordering between normal and ordered work functionsNikolay Borisov1-0/+14
Ordered work functions aren't guaranteed to be handled by the same thread which executed the normal work functions. The only way execution between normal/ordered functions is synchronized is via the WORK_DONE_BIT, unfortunately the used bitops don't guarantee any ordering whatsoever. This manifested as seemingly inexplicable crashes on ARM64, where async_chunk::inode is seen as non-null in async_cow_submit which causes submit_compressed_extents to be called and crash occurs because async_chunk::inode suddenly became NULL. The call trace was similar to: pc : submit_compressed_extents+0x38/0x3d0 lr : async_cow_submit+0x50/0xd0 sp : ffff800015d4bc20 <registers omitted for brevity> Call trace: submit_compressed_extents+0x38/0x3d0 async_cow_submit+0x50/0xd0 run_ordered_work+0xc8/0x280 btrfs_work_helper+0x98/0x250 process_one_work+0x1f0/0x4ac worker_thread+0x188/0x504 kthread+0x110/0x114 ret_from_fork+0x10/0x18 Fix this by adding respective barrier calls which ensure that all accesses preceding setting of WORK_DONE_BIT are strictly ordered before setting the flag. At the same time add a read barrier after reading of WORK_DONE_BIT in run_ordered_work which ensures all subsequent loads would be strictly ordered after reading the bit. This in turn ensures are all accesses before WORK_DONE_BIT are going to be strictly ordered before any access that can occur in ordered_func. Reported-by: Chris Murphy <lists@colorremedies.com> Fixes: 08a9ff326418 ("btrfs: Added btrfs_workqueue_struct implemented ordered execution based on kernel workqueue") CC: stable@vger.kernel.org # 4.4+ Link: https://bugzilla.redhat.com/show_bug.cgi?id=2011928 Reviewed-by: Josef Bacik <josef@toxicpanda.com> Tested-by: Chris Murphy <chris@colorremedies.com> Signed-off-by: Nikolay Borisov <nborisov@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2020-03-23Btrfs: fix crash during unmount due to race with delayed inode workersFilipe Manana1-0/+8
During unmount we can have a job from the delayed inode items work queue still running, that can lead to at least two bad things: 1) A crash, because the worker can try to create a transaction just after the fs roots were freed; 2) A transaction leak, because the worker can create a transaction before the fs roots are freed and just after we committed the last transaction and after we stopped the transaction kthread. A stack trace example of the crash: [79011.691214] kernel BUG at lib/radix-tree.c:982! [79011.692056] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC PTI [79011.693180] CPU: 3 PID: 1394 Comm: kworker/u8:2 Tainted: G W 5.6.0-rc2-btrfs-next-54 #2 (...) [79011.696789] Workqueue: btrfs-delayed-meta btrfs_work_helper [btrfs] [79011.697904] RIP: 0010:radix_tree_tag_set+0xe7/0x170 (...) [79011.702014] RSP: 0018:ffffb3c84a317ca0 EFLAGS: 00010293 [79011.702949] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 [79011.704202] RDX: ffffb3c84a317cb0 RSI: ffffb3c84a317ca8 RDI: ffff8db3931340a0 [79011.705463] RBP: 0000000000000005 R08: 0000000000000005 R09: ffffffff974629d0 [79011.706756] R10: ffffb3c84a317bc0 R11: 0000000000000001 R12: ffff8db393134000 [79011.708010] R13: ffff8db3931340a0 R14: ffff8db393134068 R15: 0000000000000001 [79011.709270] FS: 0000000000000000(0000) GS:ffff8db3b6a00000(0000) knlGS:0000000000000000 [79011.710699] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [79011.711710] CR2: 00007f22c2a0a000 CR3: 0000000232ad4005 CR4: 00000000003606e0 [79011.712958] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [79011.714205] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [79011.715448] Call Trace: [79011.715925] record_root_in_trans+0x72/0xf0 [btrfs] [79011.716819] btrfs_record_root_in_trans+0x4b/0x70 [btrfs] [79011.717925] start_transaction+0xdd/0x5c0 [btrfs] [79011.718829] btrfs_async_run_delayed_root+0x17e/0x2b0 [btrfs] [79011.719915] btrfs_work_helper+0xaa/0x720 [btrfs] [79011.720773] process_one_work+0x26d/0x6a0 [79011.721497] worker_thread+0x4f/0x3e0 [79011.722153] ? process_one_work+0x6a0/0x6a0 [79011.722901] kthread+0x103/0x140 [79011.723481] ? kthread_create_worker_on_cpu+0x70/0x70 [79011.724379] ret_from_fork+0x3a/0x50 (...) The following diagram shows a sequence of steps that lead to the crash during ummount of the filesystem: CPU 1 CPU 2 CPU 3 btrfs_punch_hole() btrfs_btree_balance_dirty() btrfs_balance_delayed_items() --> sees fs_info->delayed_root->items with value 200, which is greater than BTRFS_DELAYED_BACKGROUND (128) and smaller than BTRFS_DELAYED_WRITEBACK (512) btrfs_wq_run_delayed_node() --> queues a job for fs_info->delayed_workers to run btrfs_async_run_delayed_root() btrfs_async_run_delayed_root() --> job queued by CPU 1 --> starts picking and running delayed nodes from the prepare_list list close_ctree() btrfs_delete_unused_bgs() btrfs_commit_super() btrfs_join_transaction() --> gets transaction N btrfs_commit_transaction(N) --> set transaction state to TRANTS_STATE_COMMIT_START btrfs_first_prepared_delayed_node() --> picks delayed node X through the prepared_list list btrfs_run_delayed_items() btrfs_first_delayed_node() --> also picks delayed node X but through the node_list list __btrfs_commit_inode_delayed_items() --> runs all delayed items from this node and drops the node's item count to 0 through call to btrfs_release_delayed_inode() --> finishes running any remaining delayed nodes --> finishes transaction commit --> stops cleaner and transaction threads btrfs_free_fs_roots() --> frees all roots and removes them from the radix tree fs_info->fs_roots_radix btrfs_join_transaction() start_transaction() btrfs_record_root_in_trans() record_root_in_trans() radix_tree_tag_set() --> crashes because the root is not in the radix tree anymore If the worker is able to call btrfs_join_transaction() before the unmount task frees the fs roots, we end up leaking a transaction and all its resources, since after the call to btrfs_commit_super() and stopping the transaction kthread, we don't expect to have any transaction open anymore. When this situation happens the worker has a delayed node that has no more items to run, since the task calling btrfs_run_delayed_items(), which is doing a transaction commit, picks the same node and runs all its items first. We can not wait for the worker to complete when running delayed items through btrfs_run_delayed_items(), because we call that function in several phases of a transaction commit, and that could cause a deadlock because the worker calls btrfs_join_transaction() and the task doing the transaction commit may have already set the transaction state to TRANS_STATE_COMMIT_DOING. Also it's not possible to get into a situation where only some of the items of a delayed node are added to the fs/subvolume tree in the current transaction and the remaining ones in the next transaction, because when running the items of a delayed inode we lock its mutex, effectively waiting for the worker if the worker is running the items of the delayed node already. Since this can only cause issues when unmounting a filesystem, fix it in a simple way by waiting for any jobs on the delayed workers queue before calling btrfs_commit_supper() at close_ctree(). This works because at this point no one can call btrfs_btree_balance_dirty() or btrfs_balance_delayed_items(), and if we end up waiting for any worker to complete, btrfs_commit_super() will commit the transaction created by the worker. CC: stable@vger.kernel.org # 4.4+ Signed-off-by: Filipe Manana <fdmanana@suse.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2019-11-18btrfs: add __pure attribute to functionsDavid Sterba1-4/+2
The attribute is more relaxed than const and the functions could dereference pointers, as long as the observable state is not changed. We do have such functions, based on -Wsuggest-attribute=pure . The visible effects of this patch are negligible, there are differences in the assembly but hard to summarize. Reviewed-by: Nikolay Borisov <nborisov@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2019-11-18btrfs: get rid of pointless wtag variable in async-thread.cOmar Sandoval1-13/+8
Commit ac0c7cf8be00 ("btrfs: fix crash when tracepoint arguments are freed by wq callbacks") added a void pointer, wtag, which is passed into trace_btrfs_all_work_done() instead of the freed work item. This is silly for a few reasons: 1. The freed work item still has the same address. 2. work is still in scope after it's freed, so assigning wtag doesn't stop anyone from using it. 3. The tracepoint has always taken a void * argument, so assigning wtag doesn't actually make things any more type-safe. (Note that the original bug in commit bc074524e123 ("btrfs: prefix fsid to all trace events") was that the void * was implicitly casted when it was passed to btrfs_work_owner() in the trace point itself). Instead, let's add some clearer warnings as comments. Reviewed-by: Nikolay Borisov <nborisov@suse.com> Reviewed-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Omar Sandoval <osandov@fb.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2019-11-18btrfs: get rid of unique workqueue helper functionsOmar Sandoval1-45/+13
Commit 9e0af2376434 ("Btrfs: fix task hang under heavy compressed write") worked around the issue that a recycled work item could get a false dependency on the original work item due to how the workqueue code guarantees non-reentrancy. It did so by giving different work functions to different types of work. However, the fixes in the previous few patches are more complete, as they prevent a work item from being recycled at all (except for a tiny window that the kernel workqueue code handles for us). This obsoletes the previous fix, so we don't need the unique helpers for correctness. The only other reason to keep them would be so they show up in stack traces, but they always seem to be optimized to a tail call, so they don't show up anyways. So, let's just get rid of the extra indirection. While we're here, rename normal_work_helper() to the more informative btrfs_work_helper(). Reviewed-by: Nikolay Borisov <nborisov@suse.com> Reviewed-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Omar Sandoval <osandov@fb.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2019-11-18btrfs: don't prematurely free work in run_ordered_work()Omar Sandoval1-12/+44
We hit the following very strange deadlock on a system with Btrfs on a loop device backed by another Btrfs filesystem: 1. The top (loop device) filesystem queues an async_cow work item from cow_file_range_async(). We'll call this work X. 2. Worker thread A starts work X (normal_work_helper()). 3. Worker thread A executes the ordered work for the top filesystem (run_ordered_work()). 4. Worker thread A finishes the ordered work for work X and frees X (work->ordered_free()). 5. Worker thread A executes another ordered work and gets blocked on I/O to the bottom filesystem (still in run_ordered_work()). 6. Meanwhile, the bottom filesystem allocates and queues an async_cow work item which happens to be the recently-freed X. 7. The workqueue code sees that X is already being executed by worker thread A, so it schedules X to be executed _after_ worker thread A finishes (see the find_worker_executing_work() call in process_one_work()). Now, the top filesystem is waiting for I/O on the bottom filesystem, but the bottom filesystem is waiting for the top filesystem to finish, so we deadlock. This happens because we are breaking the workqueue assumption that a work item cannot be recycled while it still depends on other work. Fix it by waiting to free the work item until we are done with all of the related ordered work. P.S.: One might ask why the workqueue code doesn't try to detect a recycled work item. It actually does try by checking whether the work item has the same work function (find_worker_executing_work()), but in our case the function is the same. This is the only key that the workqueue code has available to compare, short of adding an additional, layer-violating "custom key". Considering that we're the only ones that have ever hit this, we should just play by the rules. Unfortunately, we haven't been able to create a minimal reproducer other than our full container setup using a compress-force=zstd filesystem on top of another compress-force=zstd filesystem. Suggested-by: Tejun Heo <tj@kernel.org> Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de> Signed-off-by: Omar Sandoval <osandov@fb.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2019-09-09btrfs: async-thread: convert defines to enumsDavid Sterba1-3/+5
Reviewed-by: Nikolay Borisov <nborisov@suse.com> Reviewed-by: Anand Jain <anand.jain@oracle.com> Signed-off-by: David Sterba <dsterba@suse.com>
2019-02-25btrfs: simplify workqueue name when allocatingDavid Sterba1-6/+4
The workqueue name is constructed from a format string but the prefix does not need to be set by %s. Reviewed-by: Nikolay Borisov <nborisov@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2018-04-12btrfs: replace GPL boilerplate by SPDX -- sourcesDavid Sterba1-14/+1
Remove GPL boilerplate text (long, short, one-line) and keep the rest, ie. personal, company or original source copyright statements. Add the SPDX header. Signed-off-by: David Sterba <dsterba@suse.com>
2017-10-30Btrfs: fix confusing worker helper info in stacktraceLiu Bo1-1/+1
We've seen the following backtrace stack in ftrace or dmesg log, kworker/u16:10-4244 [000] 241942.480955: function: btrfs_put_ordered_extent kworker/u16:10-4244 [000] 241942.480956: kernel_stack: <stack trace> => finish_ordered_fn (ffffffffa0384475) => btrfs_scrubparity_helper (ffffffffa03ca577) <-----"incorrect" => btrfs_freespace_write_helper (ffffffffa03ca98e) <-----"correct" => process_one_work (ffffffff81117b2f) => worker_thread (ffffffff81118c2a) => kthread (ffffffff81121de0) => ret_from_fork (ffffffff81d7087a) btrfs_freespace_write_helper is actually calling normal_worker_helper instead of btrfs_scrubparity_helper, so somehow kernel has parsed the incorrect function address while unwinding the stack, btrfs_scrubparity_helper really shouldn't be shown up. It's caused by compiler doing inline for our helper function, adding a noinline tag can fix that. Signed-off-by: Liu Bo <bo.li.liu@oracle.com> Reviewed-by: David Sterba <dsterba@suse.com> [ use noinline_for_stack ] Signed-off-by: David Sterba <dsterba@suse.com>
2017-08-16btrfs: constify tracepoint argumentsJeff Mahoney1-3/+3
Tracepoint arguments are all read-only. If we mark the arguments as const, we're able to keep or convert those arguments to const where appropriate. Signed-off-by: Jeff Mahoney <jeffm@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2017-01-09btrfs: fix crash when tracepoint arguments are freed by wq callbacksDavid Sterba1-4/+11
Enabling btrfs tracepoints leads to instant crash, as reported. The wq callbacks could free the memory and the tracepoints started to dereference the members to get to fs_info. The proposed fix https://marc.info/?l=linux-btrfs&m=148172436722606&w=2 removed the tracepoints but we could preserve them by passing only the required data in a safe way. Fixes: bc074524e123 ("btrfs: prefix fsid to all trace events") CC: stable@vger.kernel.org # 4.8+ Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Reviewed-by: Qu Wenruo <quwenruo@cn.fujitsu.com> Signed-off-by: David Sterba <dsterba@suse.com>
2016-12-13btrfs: limit async_work allocation and worker func durationMaxim Patlasov1-0/+14
Problem statement: unprivileged user who has read-write access to more than one btrfs subvolume may easily consume all kernel memory (eventually triggering oom-killer). Reproducer (./mkrmdir below essentially loops over mkdir/rmdir): [root@kteam1 ~]# cat prep.sh DEV=/dev/sdb mkfs.btrfs -f $DEV mount $DEV /mnt for i in `seq 1 16` do mkdir /mnt/$i btrfs subvolume create /mnt/SV_$i ID=`btrfs subvolume list /mnt |grep "SV_$i$" |cut -d ' ' -f 2` mount -t btrfs -o subvolid=$ID $DEV /mnt/$i chmod a+rwx /mnt/$i done [root@kteam1 ~]# sh prep.sh [maxim@kteam1 ~]$ for i in `seq 1 16`; do ./mkrmdir /mnt/$i 2000 2000 & done [root@kteam1 ~]# for i in `seq 1 4`; do grep "kmalloc-128" /proc/slabinfo | grep -v dma; sleep 60; done kmalloc-128 10144 10144 128 32 1 : tunables 0 0 0 : slabdata 317 317 0 kmalloc-128 9992352 9992352 128 32 1 : tunables 0 0 0 : slabdata 312261 312261 0 kmalloc-128 24226752 24226752 128 32 1 : tunables 0 0 0 : slabdata 757086 757086 0 kmalloc-128 42754240 42754240 128 32 1 : tunables 0 0 0 : slabdata 1336070 1336070 0 The huge numbers above come from insane number of async_work-s allocated and queued by btrfs_wq_run_delayed_node. The problem is caused by btrfs_wq_run_delayed_node() queuing more and more works if the number of delayed items is above BTRFS_DELAYED_BACKGROUND. The worker func (btrfs_async_run_delayed_root) processes at least BTRFS_DELAYED_BATCH items (if they are present in the list). So, the machinery works as expected while the list is almost empty. As soon as it is getting bigger, worker func starts to process more than one item at a time, it takes longer, and the chances to have async_works queued more than needed is getting higher. The problem above is worsened by another flaw of delayed-inode implementation: if async_work was queued in a throttling branch (number of items >= BTRFS_DELAYED_WRITEBACK), corresponding worker func won't quit until the number of items < BTRFS_DELAYED_BACKGROUND / 2. So, it is possible that the func occupies CPU infinitely (up to 30sec in my experiments): while the func is trying to drain the list, the user activity may add more and more items to the list. The patch fixes both problems in straightforward way: refuse queuing too many works in btrfs_wq_run_delayed_node and bail out of worker func if at least BTRFS_DELAYED_WRITEBACK items are processed. Changed in v2: remove support of thresh == NO_THRESHOLD. Signed-off-by: Maxim Patlasov <mpatlasov@virtuozzo.com> Signed-off-by: Chris Mason <clm@fb.com> Cc: stable@vger.kernel.org # v3.15+
2016-07-26btrfs: plumb fs_info into btrfs_workJeff Mahoney1-6/+25
In order to provide an fsid for trace events, we'll need a btrfs_fs_info pointer. The most lightweight way to do that for btrfs_work structures is to associate it with the __btrfs_workqueue structure. Each queued btrfs_work structure has a workqueue associated with it, so that's a natural fit. It's a privately defined structures, so we add accessors to retrieve the fs_info pointer. Signed-off-by: Jeff Mahoney <jeffm@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2016-01-25btrfs: async-thread: Fix a use-after-free error for traceQu Wenruo1-1/+1
Parameter of trace_btrfs_work_queued() can be freed in its workqueue. So no one use use that pointer after queue_work(). Fix the user-after-free bug by move the trace line before queue_work(). Reported-by: Dave Jones <davej@codemonkey.org.uk> Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: Chris Mason <clm@fb.com>
2015-12-03btrfs: use GFP_KERNEL for allocations of workqueuesDavid Sterba1-2/+2
We don't have to use GFP_NOFS to allocate workqueue structures, this is done from mount context or potentially scrub start context, safe to fail in both cases. Signed-off-by: David Sterba <dsterba@suse.com>
2015-08-31btrfs: async_thread: Fix workqueue 'max_active' value when initializingQu Wenruo1-23/+34
At initializing time, for threshold-able workqueue, it's max_active of kernel workqueue should be 1 and grow if it hits threshold. But due to the bad naming, there is both 'max_active' for kernel workqueue and btrfs workqueue. So wrong value is given at workqueue initialization. This patch fixes it, and to avoid further misunderstanding, change the member name of btrfs_workqueue to 'current_active' and 'limit_active'. Also corresponding comment is added for readability. Reported-by: Alex Lyakas <alex.btrfs@zadarastorage.com> Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com> Signed-off-by: Chris Mason <clm@fb.com>
2015-06-10btrfs: Fix lockdep warning of wr_ctx->wr_lock in scrub_free_wr_ctx()Zhao Lei1-0/+1
lockdep report following warning in test: [25176.843958] ================================= [25176.844519] [ INFO: inconsistent lock state ] [25176.845047] 4.1.0-rc3 #22 Tainted: G W [25176.845591] --------------------------------- [25176.846153] inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage. [25176.846713] fsstress/26661 [HC0[0]:SC1[1]:HE1:SE0] takes: [25176.847246] (&wr_ctx->wr_lock){+.?...}, at: [<ffffffffa04cdc6d>] scrub_free_ctx+0x2d/0xf0 [btrfs] [25176.847838] {SOFTIRQ-ON-W} state was registered at: [25176.848396] [<ffffffff810bf460>] __lock_acquire+0x6a0/0xe10 [25176.848955] [<ffffffff810bfd1e>] lock_acquire+0xce/0x2c0 [25176.849491] [<ffffffff816489af>] mutex_lock_nested+0x7f/0x410 [25176.850029] [<ffffffffa04d04ff>] scrub_stripe+0x4df/0x1080 [btrfs] [25176.850575] [<ffffffffa04d11b1>] scrub_chunk.isra.19+0x111/0x130 [btrfs] [25176.851110] [<ffffffffa04d144c>] scrub_enumerate_chunks+0x27c/0x510 [btrfs] [25176.851660] [<ffffffffa04d3b87>] btrfs_scrub_dev+0x1c7/0x6c0 [btrfs] [25176.852189] [<ffffffffa04e918e>] btrfs_dev_replace_start+0x36e/0x450 [btrfs] [25176.852771] [<ffffffffa04a98e0>] btrfs_ioctl+0x1e10/0x2d20 [btrfs] [25176.853315] [<ffffffff8121c5b8>] do_vfs_ioctl+0x318/0x570 [25176.853868] [<ffffffff8121c851>] SyS_ioctl+0x41/0x80 [25176.854406] [<ffffffff8164da17>] system_call_fastpath+0x12/0x6f [25176.854935] irq event stamp: 51506 [25176.855511] hardirqs last enabled at (51506): [<ffffffff810d4ce5>] vprintk_emit+0x225/0x5e0 [25176.856059] hardirqs last disabled at (51505): [<ffffffff810d4b77>] vprintk_emit+0xb7/0x5e0 [25176.856642] softirqs last enabled at (50886): [<ffffffff81067a23>] __do_softirq+0x363/0x640 [25176.857184] softirqs last disabled at (50949): [<ffffffff8106804d>] irq_exit+0x10d/0x120 [25176.857746] other info that might help us debug this: [25176.858845] Possible unsafe locking scenario: [25176.859981] CPU0 [25176.860537] ---- [25176.861059] lock(&wr_ctx->wr_lock); [25176.861705] <Interrupt> [25176.862272] lock(&wr_ctx->wr_lock); [25176.862881] *** DEADLOCK *** Reason: Above warning is caused by: Interrupt -> bio_endio() -> ... -> scrub_put_ctx() -> scrub_free_ctx() *1 -> ... -> mutex_lock(&wr_ctx->wr_lock); scrub_put_ctx() is allowed to be called in end_bio interrupt, but in code design, it will never call scrub_free_ctx(sctx) in interrupe context(above *1), because btrfs_scrub_dev() get one additional reference of sctx->refs, which makes scrub_free_ctx() only called withine btrfs_scrub_dev(). Now the code runs out of our wish, because free sequence in scrub_pending_bio_dec() have a gap. Current code: -----------------------------------+----------------------------------- scrub_pending_bio_dec() | btrfs_scrub_dev -----------------------------------+----------------------------------- atomic_dec(&sctx->bios_in_flight); | wake_up(&sctx->list_wait); | | scrub_put_ctx() | -> atomic_dec_and_test(&sctx->refs) scrub_put_ctx(sctx); | -> atomic_dec_and_test(&sctx->refs)| -> scrub_free_ctx() | -----------------------------------+----------------------------------- We expected: -----------------------------------+----------------------------------- scrub_pending_bio_dec() | btrfs_scrub_dev -----------------------------------+----------------------------------- atomic_dec(&sctx->bios_in_flight); | wake_up(&sctx->list_wait); | scrub_put_ctx(sctx); | -> atomic_dec_and_test(&sctx->refs)| | scrub_put_ctx() | -> atomic_dec_and_test(&sctx->refs) | -> scrub_free_ctx() -----------------------------------+----------------------------------- Fix: Move scrub_pending_bio_dec() to a workqueue, to avoid this function run in interrupt context. Tested by check tracelog in debug. Changelog v1->v2: Use workqueue instead of adjust function call sequence in v1, because v1 will introduce a bug pointed out by: Filipe David Manana <fdmanana@gmail.com> Reported-by: Qu Wenruo <quwenruo@cn.fujitsu.com> Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com> Reviewed-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Chris Mason <clm@fb.com>
2015-02-16btrfs: use correct type for workqueue flagsDavid Sterba1-2/+2
Through all the local wrappers to alloc_workqueue, __alloc_workqueue_key takes an unsigned int. Signed-off-by: David Sterba <dsterba@suse.cz>
2014-10-02btrfs: remove unlikely from NULL checksDavid Sterba1-5/+5
Unlikely is implicit for NULL checks of pointers. Signed-off-by: David Sterba <dsterba@suse.cz>
2014-09-17Btrfs: implement repair function when direct read failsMiao Xie1-0/+1
This patch implement data repair function when direct read fails. The detail of the implementation is: - When we find the data is not right, we try to read the data from the other mirror. - When the io on the mirror ends, we will insert the endio work into the dedicated btrfs workqueue, not common read endio workqueue, because the original endio work is still blocked in the btrfs endio workqueue, if we insert the endio work of the io on the mirror into that workqueue, deadlock would happen. - After we get right data, we write it back to the corrupted mirror. - And if the data on the new mirror is still corrupted, we will try next mirror until we read right data or all the mirrors are traversed. - After the above work, we set the uptodate flag according to the result. Signed-off-by: Miao Xie <miaox@cn.fujitsu.com> Signed-off-by: Chris Mason <clm@fb.com>
2014-08-24Btrfs: fix task hang under heavy compressed writeLiu Bo1-8/+36
This has been reported and discussed for a long time, and this hang occurs in both 3.15 and 3.16. Btrfs now migrates to use kernel workqueue, but it introduces this hang problem. Btrfs has a kind of work queued as an ordered way, which means that its ordered_func() must be processed in the way of FIFO, so it usually looks like -- normal_work_helper(arg) work = container_of(arg, struct btrfs_work, normal_work); work->func() <---- (we name it work X) for ordered_work in wq->ordered_list ordered_work->ordered_func() ordered_work->ordered_free() The hang is a rare case, first when we find free space, we get an uncached block group, then we go to read its free space cache inode for free space information, so it will file a readahead request btrfs_readpages() for page that is not in page cache __do_readpage() submit_extent_page() btrfs_submit_bio_hook() btrfs_bio_wq_end_io() submit_bio() end_workqueue_bio() <--(ret by the 1st endio) queue a work(named work Y) for the 2nd also the real endio() So the hang occurs when work Y's work_struct and work X's work_struct happens to share the same address. A bit more explanation, A,B,C -- struct btrfs_work arg -- struct work_struct kthread: worker_thread() pick up a work_struct from @worklist process_one_work(arg) worker->current_work = arg; <-- arg is A->normal_work worker->current_func(arg) normal_work_helper(arg) A = container_of(arg, struct btrfs_work, normal_work); A->func() A->ordered_func() A->ordered_free() <-- A gets freed B->ordered_func() submit_compressed_extents() find_free_extent() load_free_space_inode() ... <-- (the above readhead stack) end_workqueue_bio() btrfs_queue_work(work C) B->ordered_free() As if work A has a high priority in wq->ordered_list and there are more ordered works queued after it, such as B->ordered_func(), its memory could have been freed before normal_work_helper() returns, which means that kernel workqueue code worker_thread() still has worker->current_work pointer to be work A->normal_work's, ie. arg's address. Meanwhile, work C is allocated after work A is freed, work C->normal_work and work A->normal_work are likely to share the same address(I confirmed this with ftrace output, so I'm not just guessing, it's rare though). When another kthread picks up work C->normal_work to process, and finds our kthread is processing it(see find_worker_executing_work()), it'll think work C as a collision and skip then, which ends up nobody processing work C. So the situation is that our kthread is waiting forever on work C. Besides, there're other cases that can lead to deadlock, but the real problem is that all btrfs workqueue shares one work->func, -- normal_work_helper, so this makes each workqueue to have its own helper function, but only a wraper pf normal_work_helper. With this patch, I no long hit the above hang. Signed-off-by: Liu Bo <bo.li.liu@oracle.com> Signed-off-by: Chris Mason <clm@fb.com>
2014-04-07btrfs: fix crash in remount(thread_pool=) caseSergei Trofimovich1-0/+2
Reproducer: mount /dev/ubda /mnt mount -oremount,thread_pool=42 /mnt Gives a crash: ? btrfs_workqueue_set_max+0x0/0x70 btrfs_resize_thread_pool+0xe3/0xf0 ? sync_filesystem+0x0/0xc0 ? btrfs_resize_thread_pool+0x0/0xf0 btrfs_remount+0x1d2/0x570 ? kern_path+0x0/0x80 do_remount_sb+0xd9/0x1c0 do_mount+0x26a/0xbf0 ? kfree+0x0/0x1b0 SyS_mount+0xc4/0x110 It's a call btrfs_workqueue_set_max(fs_info->scrub_wr_completion_workers, new_pool_size); with fs_info->scrub_wr_completion_workers = NULL; as scrub wqs get created only on user's demand. Patch skips not-created-yet workqueues. Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org> CC: Qu Wenruo <quwenruo@cn.fujitsu.com> CC: Chris Mason <clm@fb.com> CC: Josef Bacik <jbacik@fb.com> CC: linux-btrfs@vger.kernel.org Signed-off-by: Chris Mason <clm@fb.com>
2014-03-20btrfs: Add trace for btrfs_workqueue alloc/destroyQu Wenruo1-2/+5
Since most of the btrfs_workqueue is printed as pointer address, for easier analysis, add trace for btrfs_workqueue alloc/destroy. So it is possible to determine the workqueue that a given work belongs to(by comparing the wq pointer address with alloc trace event). Signed-off-by: Qu Wenruo <quenruo@cn.fujitsu.com> Signed-off-by: Chris Mason <clm@fb.com>
2014-03-20Btrfs: add missing kfree in btrfs_destroy_workqueueFilipe Manana1-0/+1
Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com> Signed-off-by: Chris Mason <clm@fb.com>
2014-03-10btrfs: Add ftrace for btrfs_workqueueQu Wenruo1-0/+7
Add ftrace for btrfs_workqueue for further workqueue tunning. This patch needs to applied after the workqueue replace patchset. Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com> Signed-off-by: Josef Bacik <jbacik@fb.com>
2014-03-10btrfs: Cleanup the btrfs_workqueue related function typeQu Wenruo1-3/+3
The new btrfs_workqueue still use open-coded function defition, this patch will change them into btrfs_func_t type which is much the same as kernel workqueue. Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com> Signed-off-by: Josef Bacik <jbacik@fb.com>
2014-03-10btrfs: Cleanup the "_struct" suffix in btrfs_workequeueQu Wenruo1-33/+33
Since the "_struct" suffix is mainly used for distinguish the differnt btrfs_work between the original and the newly created one, there is no need using the suffix since all btrfs_workers are changed into btrfs_workqueue. Also this patch fixed some codes whose code style is changed due to the too long "_struct" suffix. Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com> Tested-by: David Sterba <dsterba@suse.cz> Signed-off-by: Josef Bacik <jbacik@fb.com>
2014-03-10btrfs: Cleanup the old btrfs_worker.Qu Wenruo1-704/+3
Since all the btrfs_worker is replaced with the newly created btrfs_workqueue, the old codes can be easily remove. Signed-off-by: Quwenruo <quwenruo@cn.fujitsu.com> Tested-by: David Sterba <dsterba@suse.cz> Signed-off-by: Josef Bacik <jbacik@fb.com>
2014-03-10btrfs: Add threshold workqueue based on kernel workqueueQu Wenruo1-8/+99
The original btrfs_workers has thresholding functions to dynamically create or destroy kthreads. Though there is no such function in kernel workqueue because the worker is not created manually, we can still use the workqueue_set_max_active to simulated the behavior, mainly to achieve a better HDD performance by setting a high threshold on submit_workers. (Sadly, no resource can be saved) So in this patch, extra workqueue pending counters are introduced to dynamically change the max active of each btrfs_workqueue_struct, hoping to restore the behavior of the original thresholding function. Also, workqueue_set_max_active use a mutex to protect workqueue_struct, which is not meant to be called too frequently, so a new interval mechanism is applied, that will only call workqueue_set_max_active after a count of work is queued. Hoping to balance both the random and sequence performance on HDD. Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com> Tested-by: David Sterba <dsterba@suse.cz> Signed-off-by: Josef Bacik <jbacik@fb.com>
2014-03-10btrfs: Add high priority workqueue support for btrfs_workqueue_structQu Wenruo1-12/+79
Add high priority function to btrfs_workqueue. This is implemented by embedding a btrfs_workqueue into a btrfs_workqueue and use some helper functions to differ the normal priority wq and high priority wq. So the high priority wq is completely independent from the normal workqueue. Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com> Tested-by: David Sterba <dsterba@suse.cz> Signed-off-by: Josef Bacik <jbacik@fb.com>
2014-03-10btrfs: Added btrfs_workqueue_struct implemented ordered execution based on ↵Qu Wenruo1-0/+137
kernel workqueue Use kernel workqueue to implement a new btrfs_workqueue_struct, which has the ordering execution feature like the btrfs_worker. The func is executed in a concurrency way, and the ordred_func/ordered_free is executed in the sequence them are queued after the corresponding func is done. The new btrfs_workqueue works much like the original one, one workqueue for normal work and a list for ordered work. When a work is queued, ordered work will be added to the list and helper function will be queued into the workqueue. The helper function will execute a normal work and then check and execute as many ordered work as possible in the sequence they were queued. At this patch, high priority work queue or thresholding is not added yet. The high priority feature and thresholding will be added in the following patches. Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Tested-by: David Sterba <dsterba@suse.cz> Signed-off-by: Josef Bacik <jbacik@fb.com>
2014-03-10btrfs: always choose work from prio_head firstStanislaw Gruszka1-4/+5
In case we do not refill, we can overwrite cur pointer from prio_head by one from not prioritized head, what looks as something that was not intended. This change make we always take works from prio_head first until it's not empty. Signed-off-by: Stanislaw Gruszka <stf_xl@wp.pl> Signed-off-by: Josef Bacik <jbacik@fb.com>
2013-11-20Btrfs: fix __btrfs_start_workers retvalIlya Dryomov1-0/+1
__btrfs_start_workers returns 0 in case it raced with btrfs_stop_workers and lost the race. This is wrong because worker in this case is not allowed to start and is in fact destroyed. Return -EINVAL instead. Signed-off-by: Ilya Dryomov <idryomov@gmail.com> Signed-off-by: Josef Bacik <jbacik@fusionio.com> Signed-off-by: Chris Mason <chris.mason@fusionio.com>
2013-11-11btrfs: Fix checkpatch.pl warning of spacing issuesDulshani Gunawardhana1-1/+1
Fix spacing issues detected via checkpatch.pl in accordance with the kernel style guidelines. Signed-off-by: Dulshani Gunawardhana <dulshani.gunawardhana89@gmail.com> Signed-off-by: Josef Bacik <jbacik@fusionio.com> Signed-off-by: Chris Mason <chris.mason@fusionio.com>
2013-10-04Btrfs: eliminate races in worker stopping codeIlya Dryomov1-6/+19
The current implementation of worker threads in Btrfs has races in worker stopping code, which cause all kinds of panics and lockups when running btrfs/011 xfstest in a loop. The problem is that btrfs_stop_workers is unsynchronized with respect to check_idle_worker, check_busy_worker and __btrfs_start_workers. E.g., check_idle_worker race flow: btrfs_stop_workers(): check_idle_worker(aworker): - grabs the lock - splices the idle list into the working list - removes the first worker from the working list - releases the lock to wait for its kthread's completion - grabs the lock - if aworker is on the working list, moves aworker from the working list to the idle list - releases the lock - grabs the lock - puts the worker - removes the second worker from the working list ...... btrfs_stop_workers returns, aworker is on the idle list FS is umounted, memory is freed ...... aworker is waken up, fireworks ensue With this applied, I wasn't able to trigger the problem in 48 hours, whereas previously I could reliably reproduce at least one of these races within an hour. Reported-by: David Sterba <dsterba@suse.cz> Signed-off-by: Ilya Dryomov <idryomov@gmail.com> Signed-off-by: Josef Bacik <jbacik@fusionio.com>
2012-07-25Btrfs: call the ordered free operation without any locks heldChris Mason1-1/+8
Each ordered operation has a free callback, and this was called with the worker spinlock held. Josef made the free callback also call iput, which we can't do with the spinlock. This drops the spinlock for the free operation and grabs it again before moving through the rest of the list. We'll circle back around to this and find a cleaner way that doesn't bounce the lock around so much. Signed-off-by: Chris Mason <chris.mason@fusionio.com> cc: stable@kernel.org
2012-03-22btrfs: return void in functions without error conditionsJeff Mahoney1-10/+5
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
2011-12-25Merge branch 'pm-sleep' into pm-for-linusRafael J. Wysocki1-1/+1
* pm-sleep: (51 commits) PM: Drop generic_subsys_pm_ops PM / Sleep: Remove forward-only callbacks from AMBA bus type PM / Sleep: Remove forward-only callbacks from platform bus type PM: Run the driver callback directly if the subsystem one is not there PM / Sleep: Make pm_op() and pm_noirq_op() return callback pointers PM / Sleep: Merge internal functions in generic_ops.c PM / Sleep: Simplify generic system suspend callbacks PM / Hibernate: Remove deprecated hibernation snapshot ioctls PM / Sleep: Fix freezer failures due to racy usermodehelper_is_disabled() PM / Sleep: Recommend [un]lock_system_sleep() over using pm_mutex directly PM / Sleep: Replace mutex_[un]lock(&pm_mutex) with [un]lock_system_sleep() PM / Sleep: Make [un]lock_system_sleep() generic PM / Sleep: Use the freezer_count() functions in [un]lock_system_sleep() APIs PM / Freezer: Remove the "userspace only" constraint from freezer[_do_not]_count() PM / Hibernate: Replace unintuitive 'if' condition in kernel/power/user.c with 'else' Freezer / sunrpc / NFS: don't allow TASK_KILLABLE sleeps to block the freezer PM / Sleep: Unify diagnostic messages from device suspend/resume ACPI / PM: Do not save/restore NVS on Asus K54C/K54HR PM / Hibernate: Remove deprecated hibernation test modes PM / Hibernate: Thaw processes in SNAPSHOT_CREATE_IMAGE ioctl test path ... Conflicts: kernel/kmod.c
2011-12-23Btrfs: fix worker lock misuse in find_workerChris Mason1-1/+2
Dan Carpenter noticed that we were doing a double unlock on the worker lock, and sometimes picking a worker thread without the lock held. This fixes both errors. Signed-off-by: Chris Mason <chris.mason@oracle.com> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
2011-12-21Merge branch 'master' into pm-sleepRafael J. Wysocki1-62/+55
* master: (848 commits) SELinux: Fix RCU deref check warning in sel_netport_insert() binary_sysctl(): fix memory leak mm/vmalloc.c: remove static declaration of va from __get_vm_area_node ipmi_watchdog: restore settings when BMC reset oom: fix integer overflow of points in oom_badness memcg: keep root group unchanged if creation fails nilfs2: potential integer overflow in nilfs_ioctl_clean_segments() nilfs2: unbreak compat ioctl cpusets: stall when updating mems_allowed for mempolicy or disjoint nodemask evm: prevent racing during tfm allocation evm: key must be set once during initialization mmc: vub300: fix type of firmware_rom_wait_states module parameter Revert "mmc: enable runtime PM by default" mmc: sdhci: remove "state" argument from sdhci_suspend_host x86, dumpstack: Fix code bytes breakage due to missing KERN_CONT IB/qib: Correct sense on freectxts increment and decrement RDMA/cma: Verify private data length cgroups: fix a css_set not found bug in cgroup_attach_proc oprofile: Fix uninitialized memory access when writing to writing to oprofilefs Revert "xen/pv-on-hvm kexec: add xs_reset_watches to shutdown watches from old kernel" ... Conflicts: kernel/cgroup_freezer.c
2011-12-15Merge branch 'for-chris' of ↵Chris Mason1-61/+54
http://git.kernel.org/pub/scm/linux/kernel/git/josef/btrfs-work into integration Conflicts: fs/btrfs/inode.c Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-12-15Btrfs: fix num_workers_starting bug and other bugs in async threadJosef Bacik1-61/+54
Al pointed out we have some random problems with the way we account for num_workers_starting in the async thread stuff. First of all we need to make sure to decrement num_workers_starting if we fail to start the worker, so make __btrfs_start_workers do this. Also fix __btrfs_start_workers so that it doesn't call btrfs_stop_workers(), there is no point in stopping everybody if we failed to create a worker. Also check_pending_worker_creates needs to call __btrfs_start_work in it's work function since it already increments num_workers_starting. People only start one worker at a time, so get rid of the num_workers argument everywhere, and make btrfs_queue_worker a void since it will always succeed. Thanks, Signed-off-by: Josef Bacik <josef@redhat.com>
2011-12-15Btrfs: add a cond_resched() into the worker loopChris Mason1-1/+1
If we have a constant stream of end_io completions or crc work, we can hit softlockup messages from the async helper threads. This adds a cond_resched() into the loop to avoid them. Signed-off-by: Chris Mason <chris.mason@oracle.com>
2011-11-21freezer: unexport refrigerator() and update try_to_freeze() slightlyTejun Heo1-1/+1
There is no reason to export two functions for entering the refrigerator. Calling refrigerator() instead of try_to_freeze() doesn't save anything noticeable or removes any race condition. * Rename refrigerator() to __refrigerator() and make it return bool indicating whether it scheduled out for freezing. * Update try_to_freeze() to return bool and relay the return value of __refrigerator() if freezing(). * Convert all refrigerator() users to try_to_freeze(). * Update documentation accordingly. * While at it, add might_sleep() to try_to_freeze(). Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Samuel Ortiz <samuel@sortiz.org> Cc: Chris Mason <chris.mason@oracle.com> Cc: "Theodore Ts'o" <tytso@mit.edu> Cc: Steven Whitehouse <swhiteho@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Jan Kara <jack@suse.cz> Cc: KONISHI Ryusuke <konishi.ryusuke@lab.ntt.co.jp> Cc: Christoph Hellwig <hch@infradead.org>
2010-05-25Btrfs: don't walk around with task->state != TASK_RUNNINGChris Mason1-0/+1
Yan Zheng noticed two places we were doing a lot of work without task->state set to TASK_RUNNING. This sets the state properly after we get ready to sleep but decide not to. Signed-off-by: Chris Mason <chris.mason@oracle.com>
2010-03-30include cleanup: Update gfp.h and slab.h includes to prepare for breaking ↵Tejun Heo1-0/+1
implicit slab.h inclusion from percpu.h percpu.h is included by sched.h and module.h and thus ends up being included when building most .c files. percpu.h includes slab.h which in turn includes gfp.h making everything defined by the two files universally available and complicating inclusion dependencies. percpu.h -> slab.h dependency is about to be removed. Prepare for this change by updating users of gfp and slab facilities include those headers directly instead of assuming availability. As this conversion needs to touch large number of source files, the following script is used as the basis of conversion. http://userweb.kernel.org/~tj/misc/slabh-sweep.py The script does the followings. * Scan files for gfp and slab usages and update includes such that only the necessary includes are there. ie. if only gfp is used, gfp.h, if slab is used, slab.h. * When the script inserts a new include, it looks at the include blocks and try to put the new include such that its order conforms to its surrounding. It's put in the include block which contains core kernel includes, in the same order that the rest are ordered - alphabetical, Christmas tree, rev-Xmas-tree or at the end if there doesn't seem to be any matching order. * If the script can't find a place to put a new include (mostly because the file doesn't have fitting include block), it prints out an error message indicating which .h file needs to be added to the file. The conversion was done in the following steps. 1. The initial automatic conversion of all .c files updated slightly over 4000 files, deleting around 700 includes and adding ~480 gfp.h and ~3000 slab.h inclusions. The script emitted errors for ~400 files. 2. Each error was manually checked. Some didn't need the inclusion, some needed manual addition while adding it to implementation .h or embedding .c file was more appropriate for others. This step added inclusions to around 150 files. 3. The script was run again and the output was compared to the edits from #2 to make sure no file was left behind. 4. Several build tests were done and a couple of problems were fixed. e.g. lib/decompress_*.c used malloc/free() wrappers around slab APIs requiring slab.h to be added manually. 5. The script was run on all .h files but without automatically editing them as sprinkling gfp.h and slab.h inclusions around .h files could easily lead to inclusion dependency hell. Most gfp.h inclusion directives were ignored as stuff from gfp.h was usually wildly available and often used in preprocessor macros. Each slab.h inclusion directive was examined and added manually as necessary. 6. percpu.h was updated not to include slab.h. 7. Build test were done on the following configurations and failures were fixed. CONFIG_GCOV_KERNEL was turned off for all tests (as my distributed build env didn't work with gcov compiles) and a few more options had to be turned off depending on archs to make things build (like ipr on powerpc/64 which failed due to missing writeq). * x86 and x86_64 UP and SMP allmodconfig and a custom test config. * powerpc and powerpc64 SMP allmodconfig * sparc and sparc64 SMP allmodconfig * ia64 SMP allmodconfig * s390 SMP allmodconfig * alpha SMP allmodconfig * um on x86_64 SMP allmodconfig 8. percpu.h modifications were reverted so that it could be applied as a separate patch and serve as bisection point. Given the fact that I had only a couple of failures from tests on step 6, I'm fairly confident about the coverage of this conversion patch. If there is a breakage, it's likely to be something in one of the arch headers which should be easily discoverable easily on most builds of the specific arch. Signed-off-by: Tejun Heo <tj@kernel.org> Guess-its-ok-by: Christoph Lameter <cl@linux-foundation.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
2009-10-05Btrfs: fix deadlock on async thread startupChris Mason1-8/+73
The btrfs async worker threads are used for a wide variety of things, including processing bio end_io functions. This means that when the endio threads aren't running, the rest of the FS isn't able to do the final processing required to clear PageWriteback. The endio threads also try to exit as they become idle and start more as the work piles up. The problem is that starting more threads means kthreadd may need to allocate ram, and that allocation may wait until the global number of writeback pages on the system is below a certain limit. The result of that throttling is that end IO threads wait on kthreadd, who is waiting on IO to end, which will never happen. This commit fixes the deadlock by handing off thread startup to a dedicated thread. It also fixes a bug where the on-demand thread creation was creating far too many threads because it didn't take into account threads being started by other procs. Signed-off-by: Chris Mason <chris.mason@oracle.com>
2009-09-15Btrfs: Fix async thread shutdown raceChris Mason1-6/+10
It was possible for an async worker thread to be selected to receive a new work item, but exit before the work item was actually placed into that thread's work list. This commit fixes the race by incrementing the num_pending counter earlier, and making sure to check the number of pending work items before a thread exits. Signed-off-by: Chris Mason <chris.mason@oracle.com>
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