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authorMing Lei <ming.lei@redhat.com>2022-04-01 16:47:32 +0300
committerMike Snitzer <snitzer@kernel.org>2022-04-01 20:23:12 +0300
commit5291984004edfcc7510024e52eaed044573b79c7 (patch)
tree886bcb0cc01c81100aa0cff22679cf942ddb5db2 /drivers/md
parentaad5b23ebf21573a32b6f07644f028d64492a5d6 (diff)
downloadlinux-5291984004edfcc7510024e52eaed044573b79c7.tar.xz
dm: fix bio polling to handle possibile BLK_STS_AGAIN
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>
Diffstat (limited to 'drivers/md')
-rw-r--r--drivers/md/dm.c20
1 files 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;
}