This is a note to let you know that I've just added the patch titled block: don't allow splitting of a REQ_NOWAIT bio to the 6.0-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: block-don-t-allow-splitting-of-a-req_nowait-bio.patch and it can be found in the queue-6.0 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 9cea62b2cbabff8ed46f2df17778b624ad9dd25a Mon Sep 17 00:00:00 2001 From: Jens Axboe <axboe@xxxxxxxxx> Date: Wed, 4 Jan 2023 08:52:06 -0700 Subject: block: don't allow splitting of a REQ_NOWAIT bio From: Jens Axboe <axboe@xxxxxxxxx> commit 9cea62b2cbabff8ed46f2df17778b624ad9dd25a upstream. 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> Reviewed-by: Keith Busch <kbusch@xxxxxxxxxx> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- block/blk-merge.c | 10 ++++++++++ 1 file changed, 10 insertions(+) --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -300,6 +300,16 @@ static struct bio *bio_split_rw(struct b *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; /* Patches currently in stable-queue which might be from axboe@xxxxxxxxx are queue-6.0/io_uring-check-for-valid-register-opcode-earlier.patch queue-6.0/arm-renumber-bits-related-to-_tif_work_mask.patch queue-6.0/ublk-honor-io_uring_f_nonblock-for-handling-control-.patch queue-6.0/io_uring-fix-cq-waiting-timeout-handling.patch queue-6.0/block-don-t-allow-splitting-of-a-req_nowait-bio.patch queue-6.0/io_uring-io-wq-free-worker-if-task_work-creation-is-canceled.patch