| Message ID | 608725.1736275167@warthog.procyon.org.uk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | netfs: Fix kernel async DIO | expand |
On Tue, 07 Jan 2025 18:39:27 +0000, David Howells wrote: > 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: > > [...] Applied to the vfs.fixes branch of the vfs/vfs.git tree. Patches in the vfs.fixes branch should appear in linux-next soon. Please report any outstanding bugs that were missed during review in a new review to the original patch series allowing us to drop it. It's encouraged to provide Acked-bys and Reviewed-bys even though the patch has now been applied. If possible patch trailers will be updated. Note that commit hashes shown below are subject to change due to rebase, trailer updates or similar. If in doubt, please check the listed branch. tree: https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git branch: vfs.fixes [1/1] netfs: Fix kernel async DIO https://git.kernel.org/vfs/vfs/c/3f6bc9e3ab9b
diff --git a/fs/netfs/direct_write.c b/fs/netfs/direct_write.c index 173e8b5e6a93..f9421f3e6d37 100644 --- a/fs/netfs/direct_write.c +++ b/fs/netfs/direct_write.c @@ -67,7 +67,7 @@ ssize_t netfs_unbuffered_write_iter_locked(struct kiocb *iocb, struct iov_iter * * allocate a sufficiently large bvec array and may shorten the * request. */ - if (async || user_backed_iter(iter)) { + if (user_backed_iter(iter)) { n = netfs_extract_user_iter(iter, len, &wreq->iter, 0); if (n < 0) { ret = n; @@ -77,6 +77,11 @@ ssize_t netfs_unbuffered_write_iter_locked(struct kiocb *iocb, struct iov_iter * wreq->direct_bv_count = n; wreq->direct_bv_unpin = iov_iter_extract_will_pin(iter); } else { + /* If this is a kernel-generated async DIO request, + * assume that any resources the iterator points to + * (eg. a bio_vec array) will persist till the end of + * the op. + */ wreq->iter = *iter; }
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@3xo.fr> Closes: https://lore.kernel.org/r/fedd8a40d54b2969097ffa4507979858@3xo.fr/ Signed-off-by: David Howells <dhowells@redhat.com> Tested-by: Nicolas Baranger <nicolas.baranger@3xo.fr> Acked-by: Paulo Alcantara (Red Hat) <pc@manguebit.com> cc: Steve French <smfrench@gmail.com> cc: Jeff Layton <jlayton@kernel.org> cc: netfs@lists.linux.dev cc: linux-cifs@vger.kernel.org cc: linux-fsdevel@vger.kernel.org --- fs/netfs/direct_write.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)