[PATCH v4 14/21] afs: Use scoped_seqlock_read() rather than manually doing seqlock stuff

[David Howells <dhowells@redhat.com>]

This is an addendum to the patch to remove the erroneous seq |= 1 in volume
lookup loop.

Switch to using scoped_seqlock_read() as suggested by Oleg Nesterov[1].

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Li RongQing <lirongqing@baidu.com>
cc: linux-afs@lists.infradead.org
Link: https://lore.kernel.org/r/aifaeKvz3KemfzaS@redhat.com/ [1]
---
 fs/afs/callback.c | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/fs/afs/callback.c b/fs/afs/callback.c
index 833ac3178ddc..dd7a407ea368 100644
--- a/fs/afs/callback.c
+++ b/fs/afs/callback.c
@@ -113,16 +113,12 @@ static struct afs_volume *afs_lookup_volume_rcu(struct afs_cell *cell,
 {
 	struct afs_volume *volume = NULL;
 	struct rb_node *p;
-	int seq = 1;
 
-	for (;;) {
+	scoped_seqlock_read(&cell->volume_lock, ss_lock) {
 		/* Unfortunately, rbtree walking doesn't give reliable results
 		 * under just the RCU read lock, so we have to check for
 		 * changes.
 		 */
-		seq++; /* 2 on the 1st/lockless path, otherwise odd */
-		read_seqbegin_or_lock(&cell->volume_lock, &seq);
-
 		p = rcu_dereference_raw(cell->volumes.rb_node);
 		while (p) {
 			volume = rb_entry(p, struct afs_volume, cell_node);
@@ -138,11 +134,8 @@ static struct afs_volume *afs_lookup_volume_rcu(struct afs_cell *cell,
 
 		if (volume && afs_try_get_volume(volume, afs_volume_trace_get_callback))
 			break;
-		if (!need_seqretry(&cell->volume_lock, seq))
-			break;
 	}
 
-	done_seqretry(&cell->volume_lock, seq);
 	return volume;
 }