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From: Fabian Ebner <f.ebner@proxmox.com>
To: pve-devel@lists.proxmox.com
Date: Wed, 28 Jul 2021 12:55:55 +0200
Message-Id: <20210728105555.1225184-1-f.ebner@proxmox.com>
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Subject: [pve-devel] [PATCH qemu] block/io_uring: resubmit when result is
-EAGAIN
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Quoting from [0]:
Some setups, like SCSI, can throw spurious -EAGAIN off the softirq
completion path. Normally we expect this to happen inline as part
of submission, but apparently SCSI has a weird corner case where it
can happen as part of normal completions.
Host kernels without patch [0] can panic when this happens [1], and
resubmitting makes the panic more likely. On the other hand, for
kernels with patch [0], resubmitting ensures that a block job is not
aborted just because of such spurious errors. In particular, this
should fix the problem reported in [2] with PBS backups of LVM-backed
VMs.
[0]: https://lore.kernel.org/io-uring/20210727165811.284510-3-axboe@kernel.dk/T/#u
[1]:
#9 [ffffb732000c8b70] asm_exc_page_fault at ffffffffa4800ade
#10 [ffffb732000c8bf8] io_prep_async_work at ffffffffa3d89c16
#11 [ffffb732000c8c50] io_rw_reissue at ffffffffa3d8b2e1
#12 [ffffb732000c8c78] io_complete_rw at ffffffffa3d8baa8
#13 [ffffb732000c8c98] blkdev_bio_end_io at ffffffffa3d62a80
#14 [ffffb732000c8cc8] bio_endio at ffffffffa3f4e800
#15 [ffffb732000c8ce8] dec_pending at ffffffffa432f854
#16 [ffffb732000c8d30] clone_endio at ffffffffa433170c
#17 [ffffb732000c8d70] bio_endio at ffffffffa3f4e800
#18 [ffffb732000c8d90] blk_update_request at ffffffffa3f53a37
#19 [ffffb732000c8dd0] scsi_end_request at ffffffffa4233a5c
#20 [ffffb732000c8e08] scsi_io_completion at ffffffffa423432c
#21 [ffffb732000c8e58] scsi_finish_command at ffffffffa422c527
#22 [ffffb732000c8e88] scsi_softirq_done at ffffffffa42341e4
[2]: https://forum.proxmox.com/threads/backup-job-failed-with-err-11-on-2-of-6-vms.92568/
Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>
---
Mail sent upstream:
https://lists.nongnu.org/archive/html/qemu-devel/2021-07/msg06765.html
block/io_uring.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/block/io_uring.c b/block/io_uring.c
index 00a3ee9fb8..77d162cb24 100644
--- a/block/io_uring.c
+++ b/block/io_uring.c
@@ -165,7 +165,7 @@ static void luring_process_completions(LuringState *s)
total_bytes = ret + luringcb->total_read;
if (ret < 0) {
- if (ret == -EINTR) {
+ if (ret == -EINTR || ret == -EAGAIN) {
luring_resubmit(s, luringcb);
continue;
}
--
2.30.2