Re: [PATCH v5 5/9] block: fail a short atomic pin in bio_iov_iter_get_pages()

[Hannes Reinecke]

On 9/24/26 1:56 AM, Tal Zussman wrote:
> On a partial page pin, __blkdev_direct_IO_simple() and
> __blkdev_direct_IO_async() submit what was pinned with REQ_ATOMIC set
> and leave the rest to the buffered fallback, tearing an IOCB_ATOMIC
> write.
>
> This can be triggered deterministically. A 16K pwritev2(RWF_ATOMIC)
> whose last page is PROT_NONE, on a scsi_debug device with atomic_wr=1,
> completes short with only three of the four pages written, violating
> RWF_ATOMIC semantics.
>
> Make bio_iov_iter_get_pages() release the pins and return -EINVAL when
> a REQ_ATOMIC bio doesn't cover the whole iterator, since an atomic
> write is submitted as a single bio and a short one would be torn. That
> covers iomap as well, where a partially unmapped buffer could trip the
> WARN_ON_ONCE() in iomap_dio_bio_iter_one(). The async block device path
> currently sets REQ_ATOMIC after pinning, so set it before, and move
> REQ_NOWAIT along with it.
>
> Fixes: caf336f81b3a ("block: Add fops atomic write support")
> Reported-by: Sashiko <sashiko-bot@xxxxxxxxxx>
> Link: https://sashiko.dev/#/patchset/20260802-blkdev-fixes-v1-0-a82fc549fd74%40columbia.edu?part=2
> Assisted-by: Claude:claude-fable-5
> Reviewed-by: John Garry <john.garry@xxxxxxxxx>
> Signed-off-by: Tal Zussman <tz2294@xxxxxxxxxxxx>
> ---
>   block/bio.c  | 46 ++++++++++++++++++++++++++++++----------------
>   block/fops.c | 12 ++++++------
>   2 files changed, 36 insertions(+), 22 deletions(-)
Reviewed-by: Hannes Reinecke <hare@xxxxxxxxxx>

Cheers,

Hannes
--
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@xxxxxxx                                +49 911 74053 688
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