Re: [PATCH v2] virtio-blk: Fix WARN_ON_ONCE in virtio_queue_rq()

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Wed, Aug 31, 2022 at 12:01:53AM +0900, Suwan Kim wrote:
> If a request fails at virtio_queue_rqs(), it is inserted to requeue_list
> and passed to virtio_queue_rq(). Then blk_mq_start_request() can be called
> again at virtio_queue_rq() and trigger WARN_ON_ONCE like below trace because
> request state was already set to MQ_RQ_IN_FLIGHT in virtio_queue_rqs()
> despite the failure.
> 
> [    1.890468] ------------[ cut here ]------------
> [    1.890776] WARNING: CPU: 2 PID: 122 at block/blk-mq.c:1143
> blk_mq_start_request+0x8a/0xe0
> [    1.891045] Modules linked in:
> [    1.891250] CPU: 2 PID: 122 Comm: journal-offline Not tainted 5.19.0+ #44
> [    1.891504] Hardware name: ChromiumOS crosvm, BIOS 0
> [    1.891739] RIP: 0010:blk_mq_start_request+0x8a/0xe0
> [    1.891961] Code: 12 80 74 22 48 8b 4b 10 8b 89 64 01 00 00 8b 53
> 20 83 fa ff 75 08 ba 00 00 00 80 0b 53 24 c1 e1 10 09 d1 89 48 34 5b
> 41 5e c3 <0f> 0b eb b8 65 8b 05 2b 39 b6 7e 89 c0 48 0f a3 05 39 77 5b
> 01 0f
> [    1.892443] RSP: 0018:ffffc900002777b0 EFLAGS: 00010202
> [    1.892673] RAX: 0000000000000000 RBX: ffff888004bc0000 RCX: 0000000000000000
> [    1.892952] RDX: 0000000000000000 RSI: ffff888003d7c200 RDI: ffff888004bc0000
> [    1.893228] RBP: 0000000000000000 R08: 0000000000000001 R09: ffff888004bc0100
> [    1.893506] R10: ffffffffffffffff R11: ffffffff8185ca10 R12: ffff888004bc0000
> [    1.893797] R13: ffffc90000277900 R14: ffff888004ab2340 R15: ffff888003d86e00
> [    1.894060] FS:  00007ffa143a4640(0000) GS:ffff88807dd00000(0000)
> knlGS:0000000000000000
> [    1.894412] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [    1.894682] CR2: 00005648577d9088 CR3: 00000000053da004 CR4: 0000000000170ee0
> [    1.894953] Call Trace:
> [    1.895139]  <TASK>
> [    1.895303]  virtblk_prep_rq+0x1e5/0x280
> [    1.895509]  virtio_queue_rq+0x5c/0x310
> [    1.895710]  ? virtqueue_add_sgs+0x95/0xb0
> [    1.895905]  ? _raw_spin_unlock_irqrestore+0x16/0x30
> [    1.896133]  ? virtio_queue_rqs+0x340/0x390
> [    1.896453]  ? sbitmap_get+0xfa/0x220
> [    1.896678]  __blk_mq_issue_directly+0x41/0x180
> [    1.896906]  blk_mq_plug_issue_direct+0xd8/0x2c0
> [    1.897115]  blk_mq_flush_plug_list+0x115/0x180
> [    1.897342]  blk_add_rq_to_plug+0x51/0x130
> [    1.897543]  blk_mq_submit_bio+0x3a1/0x570
> [    1.897750]  submit_bio_noacct_nocheck+0x418/0x520
> [    1.897985]  ? submit_bio_noacct+0x1e/0x260
> [    1.897989]  ext4_bio_write_page+0x222/0x420
> [    1.898000]  mpage_process_page_bufs+0x178/0x1c0
> [    1.899451]  mpage_prepare_extent_to_map+0x2d2/0x440
> [    1.899603]  ext4_writepages+0x495/0x1020
> [    1.899733]  do_writepages+0xcb/0x220
> [    1.899871]  ? __seccomp_filter+0x171/0x7e0
> [    1.900006]  file_write_and_wait_range+0xcd/0xf0
> [    1.900167]  ext4_sync_file+0x72/0x320
> [    1.900308]  __x64_sys_fsync+0x66/0xa0
> [    1.900449]  do_syscall_64+0x31/0x50
> [    1.900595]  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> [    1.900747] RIP: 0033:0x7ffa16ec96ea
> [    1.900883] Code: b8 4a 00 00 00 0f 05 48 3d 00 f0 ff ff 77 41 c3
> 48 83 ec 18 89 7c 24 0c e8 e3 02 f8 ff 8b 7c 24 0c 89 c2 b8 4a 00 00
> 00 0f 05 <48> 3d 00 f0 ff ff 77 36 89 d7 89 44 24 0c e8 43 03 f8 ff 8b
> 44 24
> [    1.901302] RSP: 002b:00007ffa143a3ac0 EFLAGS: 00000293 ORIG_RAX:
> 000000000000004a
> [    1.901499] RAX: ffffffffffffffda RBX: 0000560277ec6fe0 RCX: 00007ffa16ec96ea
> [    1.901696] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000016
> [    1.901884] RBP: 0000560277ec5910 R08: 0000000000000000 R09: 00007ffa143a4640
> [    1.902082] R10: 00007ffa16e4d39e R11: 0000000000000293 R12: 00005602773f59e0
> [    1.902459] R13: 0000000000000000 R14: 00007fffbfc007ff R15: 00007ffa13ba4000
> [    1.902763]  </TASK>
> [    1.902877] ---[ end trace 0000000000000000 ]---
> 
> To avoid calling blk_mq_start_request() twice, This patch moves the
> execution of blk_mq_start_request() to the end of virtblk_prep_rq().
> And instead of requeuing failed request to plug list in the error path of
> virtblk_add_req_batch(), it uses blk_mq_requeue_request() to change failed
> request state to MQ_RQ_IDLE. Then virtblk can safely handle the request
> on the next trial.
> 
> Fixes: 0e9911fa768f ("virtio-blk: support mq_ops->queue_rqs()")
> Reported-by: Alexandre Courbot <acourbot@chromium.org>
> Tested-by: Alexandre Courbot <acourbot@chromium.org>
> Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
> ---
> v1 -> v2
>  - Call blk_mq_start_request() after virtblk_add_req() can break the timestamp.
>    So move virtblk_add_req() before blk_mq_start_request().
>  - Use blk_mq_requeue_request() instead of requeuing failed request to plug list
>    if virtblk_add_req() fails within virtblk_add_req_batch(). 
> 
> 
>  drivers/block/virtio_blk.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)

Thanks for solving the timestamp issue. I'm not familiar enough which
blk_mq_requeue_request() to confirm this version is correct, but from
the virtio_blk perspective:

Acked-by: Stefan Hajnoczi <stefanha@redhat.com>

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