[PATCH 6.12 356/869] netfs: Fix missing locking around retry adding new subreqs

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

6.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Howells <dhowells@redhat.com>

[ Upstream commit cce18c263e9623872327ba3c956012f73c1179cc ]

Fix netfs_retry_read_subrequests() and netfs_retry_write_stream() to take
the appropriate lock when adding extra subrequests into
stream->subrequests.

Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item")
Fixes: 288ace2f57c9 ("netfs: New writeback implementation")
Closes: https://sashiko.dev/#/patchset/20260425125426.3855807-1-dhowells%40redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://patch.msgid.link/20260512123404.719402-3-dhowells@redhat.com
cc: Paulo Alcantara <pc@manguebit.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/netfs/write_collect.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/netfs/write_collect.c b/fs/netfs/write_collect.c
index c349867d74c34..ad2edf794f0ff 100644
--- a/fs/netfs/write_collect.c
+++ b/fs/netfs/write_collect.c
@@ -263,7 +263,9 @@ static void netfs_retry_write_stream(struct netfs_io_request *wreq,
 			list_for_each_entry_safe_from(subreq, tmp,
 						      &stream->subrequests, rreq_link) {
 				trace_netfs_sreq(subreq, netfs_sreq_trace_discard);
+				spin_lock_bh(&wreq->lock);
 				list_del(&subreq->rreq_link);
+				spin_unlock_bh(&wreq->lock);
 				netfs_put_subrequest(subreq, false, netfs_sreq_trace_put_done);
 				if (subreq == to)
 					break;
@@ -287,8 +289,10 @@ static void netfs_retry_write_stream(struct netfs_io_request *wreq,
 					     netfs_sreq_trace_new);
 			trace_netfs_sreq(subreq, netfs_sreq_trace_split);
 
+			spin_lock_bh(&wreq->lock);
 			list_add(&subreq->rreq_link, &to->rreq_link);
-			to = list_next_entry(to, rreq_link);
+			spin_unlock_bh(&wreq->lock);
+			to = subreq;
 			trace_netfs_sreq(subreq, netfs_sreq_trace_retry);
 
 			stream->sreq_max_len	= len;
-- 
2.53.0