Fix netfs_read_gaps() to use separate folios rather than re-using a single
sink folio to discard the unwanted data so that cifs checksum checking sees
all the data that was fetched.

Fixes: 7f84a7b9892d ("netfs: Make netfs_read_folio() handle streaming-write pages")
Reported-by: Frank Sorenson <sorenson@redhat.com>
Closes: https://lore.kernel.org/r/a385053c-1c4a-4060-a3bb-befa007ddb33@redhat.com/
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Frank Sorenson <sorenson@redhat.com>
cc: Paulo Alcantara <pc@manguebit.org>
cc: Namjae Jeon <linkinjeon@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-cifs@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
---
 fs/netfs/buffered_read.c |   34 +++++++++++++++++++---------------
 1 file changed, 19 insertions(+), 15 deletions(-)

diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c
index 424df70a5c30..105194de6e13 100644
--- a/fs/netfs/buffered_read.c
+++ b/fs/netfs/buffered_read.c
@@ -482,15 +482,14 @@ static int netfs_read_gaps(struct file *file, struct folio *folio)
 	struct netfs_group *group = netfs_folio_group(folio);
 	struct netfs_folio *finfo = netfs_folio_info(folio);
 	struct netfs_inode *ctx = netfs_inode(mapping->host);
-	struct folio *sink = NULL;
-	struct bio_vec *bvec;
+	struct bio_vec *bvec = NULL;
 	unsigned int from = finfo->dirty_offset;
 	unsigned int to = from + finfo->dirty_len;
-	unsigned int off = 0, i = 0;
+	unsigned int off = 0;
 	size_t flen = folio_size(folio);
 	size_t nr_bvec = flen / PAGE_SIZE + 2;
 	size_t part;
-	int ret;
+	int ret, i = 0, sink_from = -1, sink_to = -1;
 
 	_enter("%lx", folio->index);
 
@@ -515,24 +514,23 @@ static int netfs_read_gaps(struct file *file, struct folio *folio)
 	if (!bvec)
 		goto discard;
 
-	sink = folio_alloc(GFP_KERNEL, 0);
-	if (!sink) {
-		kfree(bvec);
-		goto discard;
-	}
-
 	trace_netfs_folio(folio, netfs_folio_trace_read_gaps);
 
-	rreq->direct_bv = bvec;
-	rreq->direct_bv_count = nr_bvec;
 	if (from > 0) {
 		bvec_set_folio(&bvec[i++], folio, from, 0);
 		off = from;
 	}
+	sink_from = i;
 	while (off < to) {
+		struct folio *sink = folio_alloc(GFP_KERNEL, 0);
+
+		if (!sink)
+			goto discard;
 		part = min_t(size_t, to - off, PAGE_SIZE);
-		bvec_set_folio(&bvec[i++], sink, part, 0);
+		bvec_set_folio(&bvec[i], sink, part, 0);
 		off += part;
+		sink_to = i;
+		i++;
 	}
 	if (to < flen)
 		bvec_set_folio(&bvec[i++], folio, flen - to, to);
@@ -553,8 +551,10 @@ static int netfs_read_gaps(struct file *file, struct folio *folio)
 		folio_mark_uptodate(folio);
 	}
 
-	if (sink)
-		folio_put(sink);
+	if (sink_to >= 0)
+		for (; sink_from <= sink_to; sink_from++)
+			folio_put(bvec_folio(&bvec[sink_from]));
+	kfree(bvec);
 	folio_unlock(folio);
 	netfs_put_request(rreq, netfs_rreq_trace_put_return);
 	return ret < 0 ? ret : 0;
@@ -563,6 +563,10 @@ static int netfs_read_gaps(struct file *file, struct folio *folio)
 	netfs_put_failed_request(rreq);
 alloc_error:
 	folio_unlock(folio);
+	if (sink_to >= 0)
+		for (; sink_from <= sink_to; sink_from++)
+			folio_put(bvec_folio(&bvec[sink_from]));
+	kfree(bvec);
 	return ret;
 }
 

On Mon, 14 Sep 2026 16:20:27 +0100, David Howells wrote:
> 
> Fix netfs_read_gaps() to use separate folios rather than re-using a single
> sink folio to discard the unwanted data so that cifs checksum checking sees
> all the data that was fetched.

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 netfs_read_gaps() to use separate sink folios
      https://git.kernel.org/vfs/vfs/c/fc3ae66514ca

David Howells <dhowells@redhat.com> writes:

>     
> Fix netfs_read_gaps() to use separate folios rather than re-using a single
> sink folio to discard the unwanted data so that cifs checksum checking sees
> all the data that was fetched.
>
> Fixes: 7f84a7b9892d ("netfs: Make netfs_read_folio() handle streaming-write pages")
> Reported-by: Frank Sorenson <sorenson@redhat.com>
> Closes: https://lore.kernel.org/r/a385053c-1c4a-4060-a3bb-befa007ddb33@redhat.com/
> Signed-off-by: David Howells <dhowells@redhat.com>
> Tested-by: Frank Sorenson <sorenson@redhat.com>
> cc: Paulo Alcantara <pc@manguebit.org>
> cc: Namjae Jeon <linkinjeon@kernel.org>
> cc: netfs@lists.linux.dev
> cc: linux-cifs@vger.kernel.org
> cc: linux-fsdevel@vger.kernel.org

Reviewed-by: Paulo Alcantara <pc@manguebit.org>