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>
20b2e3029e