[RFC PATCH 1/1] mm/slub: fix endless "No data" printing for alloc/free_traces attribute

From: Gerald Schaefer
Date: Wed Nov 17 2021 - 14:40:07 EST

Reading from alloc/free_traces attribute in /sys/kernel/debug/slab/ results
in an endless sequence of "No data". This is because slab_debugfs_start()
does not check for a "past end of file" condition and return NULL.

Fix it by adding such a check and return NULL.

Fixes: 64dd68497be7 ("mm: slub: move sysfs slab alloc/free interfaces to debugfs")
Cc: <stable@xxxxxxxxxxxxxxx> # v5.14+
Reported-by: Steffen Maier <maier@xxxxxxxxxxxxx>
Signed-off-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx>
mm/slub.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/mm/slub.c b/mm/slub.c
index f7368bfffb7a..336609671bc2 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -6115,6 +6115,11 @@ static void *slab_debugfs_next(struct seq_file *seq, void *v, loff_t *ppos)

static void *slab_debugfs_start(struct seq_file *seq, loff_t *ppos)
+ struct loc_track *t = seq->private;
+ if (*ppos > t->count)
+ return NULL;
return ppos;