On 11/26/2018 05:59 PM, Nikolay Borisov wrote:
On 26.11.18 г. 11:07 ч., Anand Jain wrote:Circular locking dependency check reports warning[1], that's because the btrfs_scrub_dev() calls the stack #0 below with, the fs_info::scrub_lock held. The test case leading to this warning.. mkfs.btrfs -fq /dev/sdb && mount /dev/sdb /btrfs btrfs scrub start -B /btrfs In fact we have fs_info::scrub_workers_refcnt to tack if the init and destroy of the scrub workers are needed. So once we have incremented and decremented the fs_info::scrub_workers_refcnt value in the thread, its ok to drop the scrub_lock, and then actually do the btrfs_destroy_workqueue() part. So this patch drops the scrub_lock before calling btrfs_destroy_workqueue(). [1] [ 76.146826] ====================================================== [ 76.147086] WARNING: possible circular locking dependency detected [ 76.147316] 4.20.0-rc3+ #41 Not tainted [ 76.147489] ------------------------------------------------------ [ 76.147722] btrfs/4065 is trying to acquire lock: [ 76.147984] 0000000038593bc0 ((wq_completion)"%s-%s""btrfs", name){+.+.}, at: flush_workqueue+0x70/0x4d0 [ 76.148337] but task is already holding lock: [ 76.148594] 0000000062392ab7 (&fs_info->scrub_lock){+.+.}, at: btrfs_scrub_dev+0x316/0x5d0 [btrfs] [ 76.148909] which lock already depends on the new lock. [ 76.149191] the existing dependency chain (in reverse order) is: [ 76.149446] -> #3 (&fs_info->scrub_lock){+.+.}: [ 76.149707] btrfs_scrub_dev+0x11f/0x5d0 [btrfs] [ 76.149924] btrfs_ioctl+0x1ac3/0x2d80 [btrfs] [ 76.150216] do_vfs_ioctl+0xa9/0x6d0 [ 76.150468] ksys_ioctl+0x60/0x90 [ 76.150716] __x64_sys_ioctl+0x16/0x20 [ 76.150911] do_syscall_64+0x50/0x180 [ 76.151182] entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 76.151469] -> #2 (&fs_devs->device_list_mutex){+.+.}: [ 76.151851] reada_start_machine_worker+0xca/0x3f0 [btrfs] [ 76.152195] normal_work_helper+0xf0/0x4c0 [btrfs] [ 76.152489] process_one_work+0x1f4/0x520 [ 76.152751] worker_thread+0x46/0x3d0 [ 76.153715] kthread+0xf8/0x130 [ 76.153912] ret_from_fork+0x3a/0x50 [ 76.154178] -> #1 ((work_completion)(&work->normal_work)){+.+.}: [ 76.154575] worker_thread+0x46/0x3d0 [ 76.154828] kthread+0xf8/0x130 [ 76.155108] ret_from_fork+0x3a/0x50 [ 76.155357] -> #0 ((wq_completion)"%s-%s""btrfs", name){+.+.}: [ 76.155751] flush_workqueue+0x9a/0x4d0 [ 76.155911] drain_workqueue+0xca/0x1a0 [ 76.156182] destroy_workqueue+0x17/0x230 [ 76.156455] btrfs_destroy_workqueue+0x5d/0x1c0 [btrfs] [ 76.156756] scrub_workers_put+0x2e/0x60 [btrfs] [ 76.156931] btrfs_scrub_dev+0x329/0x5d0 [btrfs] [ 76.157219] btrfs_ioctl+0x1ac3/0x2d80 [btrfs] [ 76.157491] do_vfs_ioctl+0xa9/0x6d0 [ 76.157742] ksys_ioctl+0x60/0x90 [ 76.157910] __x64_sys_ioctl+0x16/0x20 [ 76.158177] do_syscall_64+0x50/0x180 [ 76.158429] entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 76.158716] other info that might help us debug this: [ 76.158908] Chain exists of: (wq_completion)"%s-%s""btrfs", name --> &fs_devs->device_list_mutex --> &fs_info->scrub_lock [ 76.159629] Possible unsafe locking scenario: [ 76.160607] CPU0 CPU1 [ 76.160934] ---- ---- [ 76.161210] lock(&fs_info->scrub_lock); [ 76.161458] lock(&fs_devs->device_list_mutex); [ 76.161805] lock(&fs_info->scrub_lock); [ 76.161909] lock((wq_completion)"%s-%s""btrfs", name); [ 76.162201] *** DEADLOCK *** [ 76.162627] 2 locks held by btrfs/4065: [ 76.162897] #0: 00000000bef2775b (sb_writers#12){.+.+}, at: mnt_want_write_file+0x24/0x50 [ 76.163335] #1: 0000000062392ab7 (&fs_info->scrub_lock){+.+.}, at: btrfs_scrub_dev+0x316/0x5d0 [btrfs] [ 76.163796] stack backtrace: [ 76.163911] CPU: 1 PID: 4065 Comm: btrfs Not tainted 4.20.0-rc3+ #41 [ 76.164228] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006 [ 76.164646] Call Trace: [ 76.164872] dump_stack+0x5e/0x8b [ 76.165128] print_circular_bug.isra.37+0x1f1/0x1fe [ 76.165398] __lock_acquire+0x14aa/0x1620 [ 76.165652] lock_acquire+0xb0/0x190 [ 76.165910] ? flush_workqueue+0x70/0x4d0 [ 76.166175] flush_workqueue+0x9a/0x4d0 [ 76.166420] ? flush_workqueue+0x70/0x4d0 [ 76.166671] ? drain_workqueue+0x52/0x1a0 [ 76.166911] drain_workqueue+0xca/0x1a0 [ 76.167167] destroy_workqueue+0x17/0x230 [ 76.167428] btrfs_destroy_workqueue+0x5d/0x1c0 [btrfs] [ 76.167720] scrub_workers_put+0x2e/0x60 [btrfs] [ 76.168233] btrfs_scrub_dev+0x329/0x5d0 [btrfs] [ 76.168504] ? __sb_start_write+0x121/0x1b0 [ 76.168759] ? mnt_want_write_file+0x24/0x50 [ 76.169654] btrfs_ioctl+0x1ac3/0x2d80 [btrfs] [ 76.169934] ? find_held_lock+0x2d/0x90 [ 76.170204] ? find_held_lock+0x2d/0x90 [ 76.170450] do_vfs_ioctl+0xa9/0x6d0 [ 76.170690] ? __fget+0x101/0x1f0 [ 76.170910] ? __fget+0x5/0x1f0 [ 76.171157] ksys_ioctl+0x60/0x90 [ 76.171391] __x64_sys_ioctl+0x16/0x20 [ 76.171634] do_syscall_64+0x50/0x180 [ 76.171892] entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 76.172186] RIP: 0033:0x7f61d422e567 [ 76.172425] Code: 44 00 00 48 8b 05 29 09 2d 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d f9 08 2d 00 f7 d8 64 89 01 48 [ 76.172911] RSP: 002b:00007f61d3936d68 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 [ 76.173328] RAX: ffffffffffffffda RBX: 00000000019026b0 RCX: 00007f61d422e567 [ 76.173649] RDX: 00000000019026b0 RSI: 00000000c400941b RDI: 0000000000000003 [ 76.173909] RBP: 0000000000000000 R08: 00007f61d3937700 R09: 0000000000000000 [ 76.174244] R10: 00007f61d3937700 R11: 0000000000000246 R12: 0000000000000000 [ 76.174566] R13: 0000000000801000 R14: 0000000000000000 R15: 00007f61d3937700 [ 76.175217] btrfs (4065) used greatest stack depth: 11424 bytes left Signed-off-by: Anand Jain <anand.j...@oracle.com> --- fs/btrfs/scrub.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c index b1c2d1cdbd4b..3fc31eeef2a7 100644 --- a/fs/btrfs/scrub.c +++ b/fs/btrfs/scrub.c @@ -3757,10 +3757,13 @@ static noinline_for_stack int scrub_workers_get(struct btrfs_fs_info *fs_info,static noinline_for_stack void scrub_workers_put(struct btrfs_fs_info *fs_info){ + lockdep_assert_held(&fs_info->scrub_lock); if (--fs_info->scrub_workers_refcnt == 0) { + mutex_unlock(&fs_info->scrub_lock); btrfs_destroy_workqueue(fs_info->scrub_workers); btrfs_destroy_workqueue(fs_info->scrub_wr_completion_workers); btrfs_destroy_workqueue(fs_info->scrub_parity_workers); + mutex_lock(&fs_info->scrub_lock); }This looks ok, however:
Thanks for suggesting. 1-2 (below) can go into a new patch.
1. lockdep_assert_held should also be added to get scrub workers
ok. Added in v2 patch set.
2. scrub_workers_refcnt must eventually be converted to refcount_t type
ok. Added in v2 patch set.
and the _refcnt dropped from the name
name scrub_workers is already taken in this struct. scrub_workers_refcnt is also ok IMO.
3. Do we really need 3 workqueues for scrub? Are we really winning anything by having that many instead of one or just queueing scrub to a generic one?
yes the additional two workqueues are needed for disgustingly separate operations with in scrub, like repair bad block when dev replace, raid56 parity verification. Thanks, Anand
WARN_ON(fs_info->scrub_workers_refcnt < 0); }
