[PATCH] gfs2: Stop using rhashtable_walk_peek

[Andreas Gruenbacher]

Function rhashtable_walk_peek is problematic because there is no
guarantee that the glock previously returned still exists; when that key
is deleted, rhashtable_walk_peek can end up returning a different key,
which would cause an inconsistent glock dump.  So instead of using
rhashtable_walk_peek, keep track of the current glock in the seq file
iterator functions.

Signed-off-by: Andreas Gruenbacher <agruenba@xxxxxxxxxx>
---
 fs/gfs2/glock.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 82fb5583445c..f1fc353875d3 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -55,6 +55,7 @@ struct gfs2_glock_iter {
 	struct gfs2_sbd *sdp;		/* incore superblock           */
 	struct rhashtable_iter hti;	/* rhashtable iterator         */
 	struct gfs2_glock *gl;		/* current glock struct        */
+	bool gl_held;
 	loff_t last_pos;		/* last position               */
 };
 
@@ -1923,9 +1924,11 @@ void gfs2_glock_exit(void)
 
 static void gfs2_glock_iter_next(struct gfs2_glock_iter *gi, loff_t n)
 {
-	if (n == 0)
-		gi->gl = rhashtable_walk_peek(&gi->hti);
-	else {
+	if (n != 0 || !gi->gl) {
+		if (gi->gl_held) {
+			gfs2_glock_queue_put(gi->gl);
+			gi->gl_held = false;
+		}
 		gi->gl = rhashtable_walk_next(&gi->hti);
 		n--;
 	}
@@ -1988,7 +1991,10 @@ static void gfs2_glock_seq_stop(struct seq_file *seq, void *iter_ptr)
 {
 	struct gfs2_glock_iter *gi = seq->private;
 
-	gi->gl = NULL;
+	if (gi->gl) {
+		lockref_get(&gi->gl->gl_lockref);
+		gi->gl_held = true;
+	}
 	rhashtable_walk_stop(&gi->hti);
 }
 
@@ -2061,6 +2067,7 @@ static int __gfs2_glocks_open(struct inode *inode, struct file *file,
 		 */
 		gi->last_pos = -1;
 		gi->gl = NULL;
+		gi->gl_held = false;
 		rhashtable_walk_enter(&gl_hash_table, &gi->hti);
 	}
 	return ret;
@@ -2076,7 +2083,8 @@ static int gfs2_glocks_release(struct inode *inode, struct file *file)
 	struct seq_file *seq = file->private_data;
 	struct gfs2_glock_iter *gi = seq->private;
 
-	gi->gl = NULL;
+	if (gi->gl_held)
+		gfs2_glock_put(gi->gl);
 	rhashtable_walk_exit(&gi->hti);
 	return seq_release_private(inode, file);
 }
-- 
2.14.3