David Howells <dhowells@xxxxxxxxxx> writes:
> netfs: Fix kernel async DIO
>
> Netfslib needs to be able to handle kernel-initiated asynchronous DIO that
> is supplied with a bio_vec[] array. Currently, because of the async flag,
> this gets passed to netfs_extract_user_iter() which throws a warning and
> fails because it only handles IOVEC and UBUF iterators. This can be
> triggered through a combination of cifs and a loopback blockdev with
> something like:
>
> mount //my/cifs/share /foo
> dd if=/dev/zero of=/foo/m0 bs=4K count=1K
> losetup --sector-size 4096 --direct-io=on /dev/loop2046 /foo/m0
> echo hello >/dev/loop2046
>
> This causes the following to appear in syslog:
>
> WARNING: CPU: 2 PID: 109 at fs/netfs/iterator.c:50 netfs_extract_user_iter+0x170/0x250 [netfs]
>
> and the write to fail.
>
> Fix this by removing the check in netfs_unbuffered_write_iter_locked() that
> causes async kernel DIO writes to be handled as userspace writes. Note
> that this change relies on the kernel caller maintaining the existence of
> the bio_vec array (or kvec[] or folio_queue) until the op is complete.
>
> Fixes: 153a9961b551 ("netfs: Implement unbuffered/DIO write support")
> Reported by: Nicolas Baranger <nicolas.baranger@xxxxxx>
> Closes: https://lore.kernel.org/r/fedd8a40d54b2969097ffa4507979858@xxxxxx/
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> cc: Steve French <smfrench@xxxxxxxxx>
> cc: Jeff Layton <jlayton@xxxxxxxxxx>
> cc: netfs@xxxxxxxxxxxxxxx
> cc: linux-cifs@xxxxxxxxxxxxxxx
> cc: linux-fsdevel@xxxxxxxxxxxxxxx
> ---
> fs/netfs/direct_write.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
LGTM. Feel free to add:
Acked-by: Paulo Alcantara (Red Hat) <pc@xxxxxxxxxxxxx>
Thanks Christoph and Dave!
