[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 <agrue...@redhat.com>
---
 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