From 5291984004edfcc7510024e52eaed044573b79c7 Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Fri, 1 Apr 2022 09:47:32 -0400 Subject: [PATCH] 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 [snitzer: revised header, reused dm_io_complete's REQ_POLLED case] Signed-off-by: Mike Snitzer --- 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 ad2e0bbe..3c5fad7 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; } -- 2.7.4