[PATCH v5 02/24] netfs: Fix missing locking around retry adding new subreqs

[David Howells <dhowells@redhat.com>]

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>
cc: Paulo Alcantara <pc@manguebit.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 fs/netfs/read_retry.c  | 6 +++++-
 fs/netfs/write_retry.c | 6 +++++-
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/fs/netfs/read_retry.c b/fs/netfs/read_retry.c
index cca9ac43c077..5ec548b996d6 100644
--- a/fs/netfs/read_retry.c
+++ b/fs/netfs/read_retry.c
@@ -175,7 +175,9 @@ static void netfs_retry_read_subrequests(struct netfs_io_request *rreq)
 			list_for_each_entry_safe_from(subreq, tmp,
 						      &stream->subrequests, rreq_link) {
 				trace_netfs_sreq(subreq, netfs_sreq_trace_superfluous);
+				spin_lock(&rreq->lock);
 				list_del(&subreq->rreq_link);
+				spin_unlock(&rreq->lock);
 				netfs_put_subrequest(subreq, netfs_sreq_trace_put_done);
 				if (subreq == to)
 					break;
@@ -203,8 +205,10 @@ static void netfs_retry_read_subrequests(struct netfs_io_request *rreq)
 					     refcount_read(&subreq->ref),
 					     netfs_sreq_trace_new);
 
+			spin_lock(&rreq->lock);
 			list_add(&subreq->rreq_link, &to->rreq_link);
-			to = list_next_entry(to, rreq_link);
+			spin_unlock(&rreq->lock);
+			to = subreq;
 			trace_netfs_sreq(subreq, netfs_sreq_trace_retry);
 
 			stream->sreq_max_len	= umin(len, rreq->rsize);
diff --git a/fs/netfs/write_retry.c b/fs/netfs/write_retry.c
index 29489a23a220..32735abfa03f 100644
--- a/fs/netfs/write_retry.c
+++ b/fs/netfs/write_retry.c
@@ -130,7 +130,9 @@ 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(&wreq->lock);
 				list_del(&subreq->rreq_link);
+				spin_unlock(&wreq->lock);
 				netfs_put_subrequest(subreq, netfs_sreq_trace_put_done);
 				if (subreq == to)
 					break;
@@ -153,8 +155,10 @@ 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(&wreq->lock);
 			list_add(&subreq->rreq_link, &to->rreq_link);
-			to = list_next_entry(to, rreq_link);
+			spin_unlock(&wreq->lock);
+			to = subreq;
 			trace_netfs_sreq(subreq, netfs_sreq_trace_retry);
 
 			stream->sreq_max_len	= len;