[PATCH 4.19 101/190] btrfs: scrub: fix circular locking dependency warning

Greg Kroah-Hartman
2019-09-13T13:15:57Z

[ Upstream commit 1cec3f27168d7835ff3d23ab371cd548440131bb ]

This fixes a longstanding lockdep warning triggered by
fstests/btrfs/011.

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 -f /dev/sdb
$ mount /dev/sdb /btrfs
$ btrfs scrub start -B /btrfs

In fact we have fs_info::scrub_workers_refcnt to track 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().

[359.258534] ======================================================
[359.260305] WARNING: possible circular locking dependency detected
[359.261938] 5.0.0-rc6-default #461 Not tainted
[359.263135] ------------------------------------------------------
[359.264672] btrfs/20975 is trying to acquire lock:
[359.265927] 00000000d4d32bea ((wq_completion)"%s-%s""btrfs", name){+.+.}, at: flush_workqueue+0x87/0x540
[359.268416]
[359.268416] but task is already holding lock:
[359.270061] 0000000053ea26a6 (&fs_info->scrub_lock){+.+.}, at: btrfs_scrub_dev+0x322/0x590 [btrfs]
[359.272418]
[359.272418] which lock already depends on the new lock.
[359.272418]
[359.274692]
[359.274692] the existing dependency chain (in reverse order) is:
[359.276671]
[359.276671] -> #3 (&fs_info->scrub_lock){+.+.}:
[359.278187] __mutex_lock+0x86/0x9c0
[359.279086] btrfs_scrub_pause+0x31/0x100 [btrfs]
[359.280421] btrfs_commit_transaction+0x1e4/0x9e0 [btrfs]
[359.281931] close_ctree+0x30b/0x350 [btrfs]
[359.283208] generic_shutdown_super+0x64/0x100
[359.284516] kill_anon_super+0x14/0x30
[359.285658] btrfs_kill_super+0x12/0xa0 [btrfs]
[359.286964] deactivate_locked_super+0x29/0x60
[359.288242] cleanup_mnt+0x3b/0x70
[359.289310] task_work_run+0x98/0xc0
[359.290428] exit_to_usermode_loop+0x83/0x90
[359.291445] do_syscall_64+0x15b/0x180
[359.292598] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[359.294011]
[359.294011] -> #2 (sb_internal#2){.+.+}:
[359.295432] __sb_start_write+0x113/0x1d0
[359.296394] start_transaction+0x369/0x500 [btrfs]
[359.297471] btrfs_finish_ordered_io+0x2aa/0x7c0 [btrfs]
[359.298629] normal_work_helper+0xcd/0x530 [btrfs]
[359.299698] process_one_work+0x246/0x610
[359.300898] worker_thread+0x3c/0x390
[359.302020] kthread+0x116/0x130
[359.303053] ret_from_fork+0x24/0x30
[359.304152]
[359.304152] -> #1 ((work_completion)(&work->normal_work)){+.+.}:
[359.306100] process_one_work+0x21f/0x610
[359.307302] worker_thread+0x3c/0x390
[359.308465] kthread+0x116/0x130
[359.309357] ret_from_fork+0x24/0x30
[359.310229]
[359.310229] -> #0 ((wq_completion)"%s-%s""btrfs", name){+.+.}:
[359.311812] lock_acquire+0x90/0x180
[359.312929] flush_workqueue+0xaa/0x540
[359.313845] drain_workqueue+0xa1/0x180
[359.314761] destroy_workqueue+0x17/0x240
[359.315754] btrfs_destroy_workqueue+0x57/0x200 [btrfs]
[359.317245] scrub_workers_put+0x2c/0x60 [btrfs]
[359.318585] btrfs_scrub_dev+0x336/0x590 [btrfs]
[359.319944] btrfs_dev_replace_by_ioctl.cold.19+0x179/0x1bb [btrfs]
[359.321622] btrfs_ioctl+0x28a4/0x2e40 [btrfs]
[359.322908] do_vfs_ioctl+0xa2/0x6d0
[359.324021] ksys_ioctl+0x3a/0x70
[359.325066] __x64_sys_ioctl+0x16/0x20
[359.326236] do_syscall_64+0x54/0x180
[359.327379] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[359.328772]
[359.328772] other info that might help us debug this:
[359.328772]
[359.330990] Chain exists of:
[359.330990] (wq_completion)"%s-%s""btrfs", name --> sb_internal#2 --> &fs_info->scrub_lock
[359.330990]
[359.334376] Possible unsafe locking scenario:
[359.334376]
[359.336020] CPU0 CPU1
[359.337070] ---- ----
[359.337821] lock(&fs_info->scrub_lock);
[359.338506] lock(sb_internal#2);
[359.339506] lock(&fs_info->scrub_lock);
[359.341461] lock((wq_completion)"%s-%s""btrfs", name);
[359.342437]
[359.342437] *** DEADLOCK ***
[359.342437]
[359.343745] 1 lock held by btrfs/20975:
[359.344788] #0: 0000000053ea26a6 (&fs_info->scrub_lock){+.+.}, at: btrfs_scrub_dev+0x322/0x590 [btrfs]
[359.346778]
[359.346778] stack backtrace:
[359.347897] CPU: 0 PID: 20975 Comm: btrfs Not tainted 5.0.0-rc6-default #461
[359.348983] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.11.2-0-gf9626cc-prebuilt.qemu-project.org 04/01/2014
[359.350501] Call Trace:
[359.350931] dump_stack+0x67/0x90
[359.351676] print_circular_bug.isra.37.cold.56+0x15c/0x195
[359.353569] check_prev_add.constprop.44+0x4f9/0x750
[359.354849] ? check_prev_add.constprop.44+0x286/0x750
[359.356505] __lock_acquire+0xb84/0xf10
[359.357505] lock_acquire+0x90/0x180
[359.358271] ? flush_workqueue+0x87/0x540
[359.359098] flush_workqueue+0xaa/0x540
[359.359912] ? flush_workqueue+0x87/0x540
[359.360740] ? drain_workqueue+0x1e/0x180
[359.361565] ? drain_workqueue+0xa1/0x180
[359.362391] drain_workqueue+0xa1/0x180
[359.363193] destroy_workqueue+0x17/0x240
[359.364539] btrfs_destroy_workqueue+0x57/0x200 [btrfs]
[359.365673] scrub_workers_put+0x2c/0x60 [btrfs]
[359.366618] btrfs_scrub_dev+0x336/0x590 [btrfs]
[359.367594] ? start_transaction+0xa1/0x500 [btrfs]
[359.368679] btrfs_dev_replace_by_ioctl.cold.19+0x179/0x1bb [btrfs]
[359.369545] btrfs_ioctl+0x28a4/0x2e40 [btrfs]
[359.370186] ? __lock_acquire+0x263/0xf10
[359.370777] ? kvm_clock_read+0x14/0x30
[359.371392] ? kvm_sched_clock_read+0x5/0x10
[359.372248] ? sched_clock+0x5/0x10
[359.372786] ? sched_clock_cpu+0xc/0xc0
[359.373662] ? do_vfs_ioctl+0xa2/0x6d0
[359.374552] do_vfs_ioctl+0xa2/0x6d0
[359.375378] ? do_sigaction+0xff/0x250
[359.376233] ksys_ioctl+0x3a/0x70
[359.376954] __x64_sys_ioctl+0x16/0x20
[359.377772] do_syscall_64+0x54/0x180
[359.378841] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[359.380422] RIP: 0033:0x7f5429296a97

Backporting to older kernels: scrub_nocow_workers must be freed the same
way as the others.

CC: stable@vger.kernel.org # 4.4+
Signed-off-by: Anand Jain <anand.jain@oracle.com>
[ update changelog ]
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 56c4d2236484f..a08a4d6f540f9 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -3778,16 +3778,6 @@ fail_scrub_workers:
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)
@@ -3796,6 +3786,9 @@ 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;
@@ -3935,9 +3928,16 @@ 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;
--
2.20.1