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>
---
v3->v4: Fix list corruption as reported by btrfs/073 by David.
[1]
https://patchwork.kernel.org/patch/10705741/
Which I was able to reproduce with an instrumented kernel but not with
btrfs/073.
In v3 patch, it releases the fs_info::scrub_lock to destroy the work
queue
which raced with new scrub requests, overwriting the scrub workers
pointers. So in v4, it kills the function scrub_workers_put(), and
performs the destroy_workqueue in two stages, with worker pointers
copied locally.
v2->v3: none
v1->v2: none
fs/btrfs/scrub.c | 22 +++++++++++-----------
1 file changed, 11 insertions(+), 11 deletions(-)
diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 33f2793bdee0..f2f0be7864b8 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -3770,16 +3770,6 @@ static noinline_for_stack int scrub_workers_get(struct
btrfs_fs_info *fs_info,
return -ENOMEM;
}
-static noinline_for_stack void scrub_workers_put(struct btrfs_fs_info *fs_info)
-{
- if (--fs_info->scrub_workers_refcnt == 0) {
- btrfs_destroy_workqueue(fs_info->scrub_workers);
- btrfs_destroy_workqueue(fs_info->scrub_wr_completion_workers);
- btrfs_destroy_workqueue(fs_info->scrub_parity_workers);
- }
- WARN_ON(fs_info->scrub_workers_refcnt < 0);
-}
-
int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64 devid, u64 start,
u64 end, struct btrfs_scrub_progress *progress,
int readonly, int is_dev_replace)
@@ -3788,6 +3778,9 @@ int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64
devid, u64 start,
int ret;
struct btrfs_device *dev;
unsigned int nofs_flag;
+ struct btrfs_workqueue *scrub_workers = NULL;
+ struct btrfs_workqueue *scrub_wr_comp = NULL;
+ struct btrfs_workqueue *scrub_parity = NULL;
if (btrfs_fs_closing(fs_info))
return -EINVAL;
@@ -3932,9 +3925,16 @@ int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64
devid, u64 start,
mutex_lock(&fs_info->scrub_lock);
dev->scrub_ctx = NULL;
- scrub_workers_put(fs_info);
+ if (--fs_info->scrub_workers_refcnt == 0) {
+ scrub_workers = fs_info->scrub_workers;
+ scrub_wr_comp = fs_info->scrub_wr_completion_workers;
+ scrub_parity = fs_info->scrub_parity_workers;
+ }
mutex_unlock(&fs_info->scrub_lock);
+ btrfs_destroy_workqueue(scrub_workers);
+ btrfs_destroy_workqueue(scrub_wr_comp);
+ btrfs_destroy_workqueue(scrub_parity);
scrub_put_ctx(sctx);
return ret;
--
1.8.3.1
