From: Jens Axboe <axboe@xxxxxxxxx> Sent: Monday, January 16, 2023 8:02 AM
>
> If we're doing a large IO request which needs to be split into multiple
> bios for issue, then we can run into the same situation as the below
> marked commit fixes - parts will complete just fine, one or more parts
> will fail to allocate a request. This will result in a partially
> completed read or write request, where the caller gets EAGAIN even though
> parts of the IO completed just fine.
>
> Do the same for large bios as we do for splits - fail a NOWAIT request
> with EAGAIN. This isn't technically fixing an issue in the below marked
> patch, but for stable purposes, we should have either none of them or
> both.
>
> This depends on: 613b14884b85 ("block: handle bio_split_to_limits() NULL return")
>
> Cc: stable@xxxxxxxxxxxxxxx # 5.15+
> Fixes: 9cea62b2cbab ("block: don't allow splitting of a REQ_NOWAIT bio")
> Link: https://github.com/axboe/liburing/issues/766
> Reported-and-tested-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
>
> ---
>
> diff --git a/block/fops.c b/block/fops.c
> index 50d245e8c913..a03cb732c2a7 100644
> --- a/block/fops.c
> +++ b/block/fops.c
> @@ -368,6 +368,14 @@ static ssize_t blkdev_direct_IO(struct kiocb *iocb, struct
> iov_iter *iter)
> return __blkdev_direct_IO_simple(iocb, iter, nr_pages);
> return __blkdev_direct_IO_async(iocb, iter, nr_pages);
> }
> + /*
> + * We're doing more than a bio worth of IO (> 256 pages), and we
> + * cannot guarantee that one of the sub bios will not fail getting
> + * issued FOR NOWAIT as error results are coalesced across all of
> + * them. Be safe and ask for a retry of this from blocking context.
> + */
> + if (iocb->ki_flags & IOCB_NOWAIT)
> + return -EAGAIN;
> return __blkdev_direct_IO(iocb, iter, bio_max_segs(nr_pages));
> }
A code observation: __blkdev_direct_IO() has a test for IOCB_NOWAIT
that now can't happen, as this is the only place it is called. But maybe it's
safer to leave the check in case of future code shuffling.
Michael
