Thanks!
I ported the patch to linus/master (see below) and it looks pretty much the
same as yours, give or take tabs getting converted to spaces.
Could I put you down as a Tested-by?
David
---
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(-)
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;
}
