Commits
Tetsuo Handa committed 1e047eaab3b
block/loop: fix deadlock after loop_set_status
syzbot is reporting deadlocks at __blkdev_get() [1].
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[ 92.493919] systemd-udevd D12696 525 1 0x00000000
[ 92.495891] Call Trace:
[ 92.501560] schedule+0x23/0x80
[ 92.502923] schedule_preempt_disabled+0x5/0x10
[ 92.504645] __mutex_lock+0x416/0x9e0
[ 92.510760] __blkdev_get+0x73/0x4f0
[ 92.512220] blkdev_get+0x12e/0x390
[ 92.518151] do_dentry_open+0x1c3/0x2f0
[ 92.519815] path_openat+0x5d9/0xdc0
[ 92.521437] do_filp_open+0x7d/0xf0
[ 92.527365] do_sys_open+0x1b8/0x250
[ 92.528831] do_syscall_64+0x6e/0x270
[ 92.530341] entry_SYSCALL_64_after_hwframe+0x42/0xb7
[ 92.931922] 1 lock held by systemd-udevd/525:
[ 92.933642] #0: 00000000a2849e25 (&bdev->bd_mutex){+.+.}, at: __blkdev_get+0x73/0x4f0
----------------------------------------
The reason of deadlock turned out that wait_event_interruptible() in
blk_queue_enter() got stuck with bdev->bd_mutex held at __blkdev_put()
due to q->mq_freeze_depth == 1.
----------------------------------------
[ 92.787172] a.out S12584 634 633 0x80000002
[ 92.789120] Call Trace:
[ 92.796693] schedule+0x23/0x80
[ 92.797994] blk_queue_enter+0x3cb/0x540
[ 92.803272] generic_make_request+0xf0/0x3d0
[ 92.807970] submit_bio+0x67/0x130
[ 92.810928] submit_bh_wbc+0x15e/0x190
[ 92.812461] __block_write_full_page+0x218/0x460
[ 92.815792] __writepage+0x11/0x50
[ 92.817209] write_cache_pages+0x1ae/0x3d0
[ 92.825585] generic_writepages+0x5a/0x90
[ 92.831865] do_writepages+0x43/0xd0
[ 92.836972] __filemap_fdatawrite_range+0xc1/0x100
[ 92.838788] filemap_write_and_wait+0x24/0x70
[ 92.840491] __blkdev_put+0x69/0x1e0
[ 92.841949] blkdev_close+0x16/0x20
[ 92.843418] __fput+0xda/0x1f0
[ 92.844740] task_work_run+0x87/0xb0
[ 92.846215] do_exit+0x2f5/0xba0
[ 92.850528] do_group_exit+0x34/0xb0
[ 92.852018] SyS_exit_group+0xb/0x10
[ 92.853449] do_syscall_64+0x6e/0x270
[ 92.854944] entry_SYSCALL_64_after_hwframe+0x42/0xb7
[ 92.943530] 1 lock held by a.out/634:
[ 92.945105] #0: 00000000a2849e25 (&bdev->bd_mutex){+.+.}, at: __blkdev_put+0x3c/0x1e0
----------------------------------------
The reason of q->mq_freeze_depth == 1 turned out that loop_set_status()
forgot to call blk_mq_unfreeze_queue() at error paths for
info->lo_encrypt_type != NULL case.
----------------------------------------
[ 37.509497] CPU: 2 PID: 634 Comm: a.out Tainted: G W 4.16.0+ #457
[ 37.513608] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 05/19/2017
[ 37.518832] RIP: 0010:blk_freeze_queue_start+0x17/0x40
[ 37.521778] RSP: 0018:ffffb0c2013e7c60 EFLAGS: 00010246
[ 37.524078] RAX: 0000000000000000 RBX: ffff8b07b1519798 RCX: 0000000000000000
[ 37.527015] RDX: 0000000000000002 RSI: ffffb0c2013e7cc0 RDI: ffff8b07b1519798
[ 37.529934] RBP: ffffb0c2013e7cc0 R08: 0000000000000008 R09: 47a189966239b898
[ 37.532684] R10: dad78b99b278552f R11: 9332dca72259d5ef R12: ffff8b07acd73678
[ 37.535452] R13: 0000000000004c04 R14: 0000000000000000 R15: ffff8b07b841e940
[ 37.538186] FS: 00007fede33b9740(0000) GS:ffff8b07b8e80000(0000) knlGS:0000000000000000
[ 37.541168] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 37.543590] CR2: 00000000206fdf18 CR3: 0000000130b30006 CR4: 00000000000606e0
[ 37.546410] Call Trace:
[ 37.547902] blk_freeze_queue+0x9/0x30
[ 37.549968] loop_set_status+0x67/0x3c0 [loop]
[ 37.549975] loop_set_status64+0x3b/0x70 [loop]
[ 37.549986] lo_ioctl+0x223/0x810 [loop]
[ 37.549995] blkdev_ioctl+0x572/0x980
[ 37.550003] block_ioctl+0x34/0x40
[ 37.550006] do_vfs_ioctl+0xa7/0x6d0
[ 37.550017] ksys_ioctl+0x6b/0x80
[ 37.573076] SyS_ioctl+0x5/0x10
[ 37.574831] do_syscall_64+0x6e/0x270
[ 37.576769] entry_SYSCALL_64_after_hwframe+0x42/0xb7
----------------------------------------
[1] https://syzkaller.appspot.com/bug?id=cd662bc3f6022c0979d01a262c318fab2ee9b56f
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: syzbot <bot+48594378e9851eab70bcd6f99327c7db58c5a28a@syzkaller.appspotmail.com>
Fixes: ecdd09597a572513 ("block/loop: fix race between I/O and set_status")
Cc: Ming Lei <tom.leiming@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: stable <stable@vger.kernel.org>
Cc: Jens Axboe <axboe@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>