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Subject[PATCH 4.4 31/41] gfs2: Fix debugfs glocks dump
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andreas Gruenbacher <agruenba@redhat.com>

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>
---
fs/gfs2/glock.c | 21 +++++++++------------
1 file changed, 9 insertions(+), 12 deletions(-)

--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -1814,13 +1814,10 @@ static void *gfs2_glock_seq_start(struct
{
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
} while (gi->gl && n--);

gi->last_pos = *pos;
+
return gi->gl;
}

@@ -1839,6 +1837,7 @@ static void *gfs2_glock_seq_next(struct
(*pos)++;
gi->last_pos = *pos;
gfs2_glock_iter_next(gi);
+
return gi->gl;
}

@@ -1847,7 +1846,10 @@ static void gfs2_glock_seq_stop(struct s
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
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 in
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 inod
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;
}

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