From 3f6bc9e3ab9b127171d39f9ac6eca1abb693b731 Mon Sep 17 00:00:00 2001 From: David Howells Date: Tue, 7 Jan 2025 18:39:27 +0000 Subject: 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 Closes: https://lore.kernel.org/r/fedd8a40d54b2969097ffa4507979858@3xo.fr/ Signed-off-by: David Howells Link: https://lore.kernel.org/r/608725.1736275167@warthog.procyon.org.uk Tested-by: Nicolas Baranger Acked-by: Paulo Alcantara (Red Hat) cc: Steve French cc: Jeff Layton cc: netfs@lists.linux.dev cc: linux-cifs@vger.kernel.org cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner --- fs/netfs/direct_write.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) (limited to 'fs') 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; } -- cgit v1.2.3