If we split a bio marked with REQ_NOWAIT, then we can trigger spurious EAGAIN if constituent parts of that split bio end up failing request allocations. Parts will complete just fine, but just a single failure in one of the chained bios will yield an EAGAIN final result for the parent bio. Return EAGAIN early if we end up needing to split such a bio, which allows for saner recovery handling. Cc: stable@xxxxxxxxxxxxxxx # 5.15+ Link: https://github.com/axboe/liburing/issues/766 Reported-by: Michael Kelley <mikelley@xxxxxxxxxxxxx> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> --- block/blk-merge.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/block/blk-merge.c b/block/blk-merge.c index 071c5f8cf0cf..b7c193d67185 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -309,6 +309,16 @@ static struct bio *bio_split_rw(struct bio *bio, const struct queue_limits *lim, *segs = nsegs; return NULL; split: + /* + * We can't sanely support splitting for a REQ_NOWAIT bio. End it + * with EAGAIN if splitting is required and return an error pointer. + */ + if (bio->bi_opf & REQ_NOWAIT) { + bio->bi_status = BLK_STS_AGAIN; + bio_endio(bio); + return ERR_PTR(-EAGAIN); + } + *segs = nsegs; /* -- 2.39.0
