block: don't allow splitting of a REQ_NOWAIT bio
authorJens Axboe <axboe@kernel.dk>
Wed, 4 Jan 2023 15:52:06 +0000 (08:52 -0700)
committerJens Axboe <axboe@kernel.dk>
Wed, 4 Jan 2023 20:24:44 +0000 (13:24 -0700)
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@vger.kernel.org # 5.15+
Link: https://github.com/axboe/liburing/issues/766
Reported-by: Michael Kelley <mikelley@microsoft.com>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
block/blk-merge.c

index 071c5f8cf0cfecbb57cdb7796731d007c0e5429e..b7c193d67185de9dc6b3a320fe49272229ebc32e 100644 (file)
@@ -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;
 
        /*