gfs2: Fix debugfs glocks dump

commit 10201655b085df8e000822e496e5d4016a167a36 upstream.

The switch to rhashtables (commit 88ffbf3e03) broke the debugfs glock
dump (/sys/kernel/debug/gfs2/<device>/glocks) for dumps bigger than a
single buffer: the right function for restarting an rhashtable iteration
from the beginning of the hash table is rhashtable_walk_enter;
rhashtable_walk_stop + rhashtable_walk_start will just resume from the
current position.

The upstream commit doesn't directly apply to 4.4.y because 4.4.y
doesn't have rhashtable_walk_enter and the following mainline commits:

  92ecd73a887c4a2b94daf5fc35179d75d1c4ef95
    gfs2: Deduplicate gfs2_{glocks,glstats}_open
  cc37a62785a584f4875788689f3fd1fa6e4eb291
    gfs2: Replace rhashtable_walk_init with rhashtable_walk_enter

Other than rhashtable_walk_enter, rhashtable_walk_init can fail.  To
handle the failure case in gfs2_glock_seq_stop, we check if
rhashtable_walk_init has initialized iter->walker; if it has not, we
must not call rhashtable_walk_stop or rhashtable_walk_exit.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 070901e..ff36f54 100644 (file)
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -1814,13 +1814,10 @@ static void *gfs2_glock_seq_start(struct seq_file *seq, loff_t *pos)
 {
        struct gfs2_glock_iter *gi = seq->private;
        loff_t n = *pos;
-       int ret;
-
-       if (gi->last_pos <= *pos)
-               n = (*pos - gi->last_pos);
 
-       ret = rhashtable_walk_start(&gi->hti);
-       if (ret)
+       if (rhashtable_walk_init(&gl_hash_table, &gi->hti) != 0)
+               return NULL;
+       if (rhashtable_walk_start(&gi->hti) != 0)
                return NULL;
 
        do {
@@ -1828,6 +1825,7 @@ static void *gfs2_glock_seq_start(struct seq_file *seq, loff_t *pos)
        } while (gi->gl && n--);
 
        gi->last_pos = *pos;
+
        return gi->gl;
 }
 
@@ -1839,6 +1837,7 @@ static void *gfs2_glock_seq_next(struct seq_file *seq, void *iter_ptr,
        (*pos)++;
        gi->last_pos = *pos;
        gfs2_glock_iter_next(gi);
+
        return gi->gl;
 }
 
@@ -1847,7 +1846,10 @@ static void gfs2_glock_seq_stop(struct seq_file *seq, void *iter_ptr)
        struct gfs2_glock_iter *gi = seq->private;
 
        gi->gl = NULL;
-       rhashtable_walk_stop(&gi->hti);
+       if (gi->hti.walker) {
+               rhashtable_walk_stop(&gi->hti);
+               rhashtable_walk_exit(&gi->hti);
+       }
 }
 
 static int gfs2_glock_seq_show(struct seq_file *seq, void *iter_ptr)
@@ -1910,12 +1912,10 @@ static int gfs2_glocks_open(struct inode *inode, struct file *file)
                struct gfs2_glock_iter *gi = seq->private;
 
                gi->sdp = inode->i_private;
-               gi->last_pos = 0;
                seq->buf = kmalloc(GFS2_SEQ_GOODSIZE, GFP_KERNEL | __GFP_NOWARN);
                if (seq->buf)
                        seq->size = GFS2_SEQ_GOODSIZE;
                gi->gl = NULL;
-               ret = rhashtable_walk_init(&gl_hash_table, &gi->hti);
        }
        return ret;
 }
@@ -1926,7 +1926,6 @@ static int gfs2_glocks_release(struct inode *inode, struct file *file)
        struct gfs2_glock_iter *gi = seq->private;
 
        gi->gl = NULL;
-       rhashtable_walk_exit(&gi->hti);
        return seq_release_private(inode, file);
 }
 
@@ -1938,12 +1937,10 @@ static int gfs2_glstats_open(struct inode *inode, struct file *file)
                struct seq_file *seq = file->private_data;
                struct gfs2_glock_iter *gi = seq->private;
                gi->sdp = inode->i_private;
-               gi->last_pos = 0;
                seq->buf = kmalloc(GFS2_SEQ_GOODSIZE, GFP_KERNEL | __GFP_NOWARN);
                if (seq->buf)
                        seq->size = GFS2_SEQ_GOODSIZE;
                gi->gl = NULL;
-               ret = rhashtable_walk_init(&gl_hash_table, &gi->hti);
        }
        return ret;
 }