From 5291984004edfcc7510024e52eaed044573b79c7 Mon Sep 17 00:00:00 2001
From: Ming Lei <ming.lei@redhat.com>
Date: Fri, 1 Apr 2022 09:47:32 -0400
Subject: [PATCH] dm: fix bio polling to handle possibile BLK_STS_AGAIN
Git-commit: 5291984004edfcc7510024e52eaed044573b79c7
Patch-mainline: v5.18-rc1
References: jsc#PED-2765
Expanded testing of DM's bio polling support (using more fio threads
to dm-linear ontop of null_blk) exposed the possibility for polled
bios to hang (repeatedly polling in io_uring) when null_blk responds
with BLK_STS_AGAIN (due to lack of resources):
1) io_complete_rw_iopoll() is called from blkdev_bio_end_io_async() to
notify kiocb is done, that is the completion interface between block
layer and io_uring
2) io_complete_rw_iopoll() is called from io_do_iopoll()
3) dm returns BLK_STS_AGAIN for one bio (on behalf of underlying
driver), then io_complete_rw_iopoll is called, but io_do_iopoll()
doesn't handle -EAGAIN at all (due to logic in io_rw_should_reissue)
4) reason for dm's BLK_STS_AGAIN is underlying null_blk driver ran out
of requests (easier to reproduce by setting low hw_queue_depth).
5) dm should handle BLK_STS_AGAIN for POLLED underlying IO, and may
retry in dm layer.
This fix adds REQ_POLLED specific BLK_STS_AGAIN handling to
dm_io_complete() that clears REQ_POLLED and requeues the bio to DM
using queue_io().
Fixes: b99fdcdc3636 ("dm: support bio polling")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
[snitzer: revised header, reused dm_io_complete's REQ_POLLED case]
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Coly Li <colyli@suse.de>
---
drivers/md/dm.c | 20 +++++++++++++-------
1 file changed, 13 insertions(+), 7 deletions(-)
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index ad2e0bbeb559..3c5fad7c4ee6 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -892,13 +892,19 @@ static void dm_io_complete(struct dm_io *io)
if (unlikely(wq_has_sleeper(&md->wait)))
wake_up(&md->wait);
- if (io_error == BLK_STS_DM_REQUEUE) {
- /*
- * Upper layer won't help us poll split bio, io->orig_bio
- * may only reflect a subset of the pre-split original,
- * so clear REQ_POLLED in case of requeue
- */
- bio->bi_opf &= ~REQ_POLLED;
+ if (io_error == BLK_STS_DM_REQUEUE || io_error == BLK_STS_AGAIN) {
+ if (bio->bi_opf & REQ_POLLED) {
+ /*
+ * Upper layer won't help us poll split bio (io->orig_bio
+ * may only reflect a subset of the pre-split original)
+ * so clear REQ_POLLED in case of requeue.
+ */
+ bio->bi_opf &= ~REQ_POLLED;
+ if (io_error == BLK_STS_AGAIN) {
+ /* io_uring doesn't handle BLK_STS_AGAIN (yet) */
+ queue_io(md, bio);
+ }
+ }
return;
}
--
2.35.3