[PATCH 5.15 062/171] mm/slub: fix endianness bug for alloc/free_traces attributes

Greg Kroah-Hartman
2021-12-13T10:23:29Z

From: Gerald Schaefer <gerald.schaefer@linux.ibm.com>

commit 005a79e5c254c3f60ec269a459cc41b55028c798 upstream.

On big-endian s390, the alloc/free_traces attributes produce endless
output, because of always 0 idx in slab_debugfs_show().

idx is de-referenced from *v, which points to a loff_t value, with

unsigned int idx = *(unsigned int *)v;

This will only give the upper 32 bits on big-endian, which remain 0.

Instead of only fixing this de-reference, during discussion it seemed
more appropriate to change the seq_ops so that they use an explicit
iterator in private loc_track struct.

This patch adds idx to loc_track, which will also fix the endianness
bug.

Link: https://lore.kernel.org/r/20211117193932.4049412-1-gerald.schaefer@linux.ibm.com
Link: https://lkml.kernel.org/r/20211126171848.17534-1-gerald.schaefer@linux.ibm.com
Fixes: 64dd68497be7 ("mm: slub: move sysfs slab alloc/free interfaces to debugfs")
Signed-off-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Reported-by: Steffen Maier <maier@linux.ibm.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Faiyaz Mohammed <faiyazm@codeaurora.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
mm/slub.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)

--- a/mm/slub.c
+++ b/mm/slub.c
@@ -5072,6 +5072,7 @@ struct loc_track {
unsigned long max;
unsigned long count;
struct location *loc;
+ loff_t idx;
};

static struct dentry *slab_debugfs_root;
@@ -6035,11 +6036,11 @@ __initcall(slab_sysfs_init);
#if defined(CONFIG_SLUB_DEBUG) && defined(CONFIG_DEBUG_FS)
static int slab_debugfs_show(struct seq_file *seq, void *v)
{
-
- struct location *l;
- unsigned int idx = *(unsigned int *)v;
struct loc_track *t = seq->private;
+ struct location *l;
+ unsigned long idx;

+ idx = (unsigned long) t->idx;
if (idx < t->count) {
l = &t->loc[idx];

@@ -6088,16 +6089,18 @@ static void *slab_debugfs_next(struct se
{
struct loc_track *t = seq->private;

- v = ppos;
- ++*ppos;
+ t->idx = ++(*ppos);
if (*ppos <= t->count)
- return v;
+ return ppos;

return NULL;
}

static void *slab_debugfs_start(struct seq_file *seq, loff_t *ppos)
{
+ struct loc_track *t = seq->private;
+
+ t->idx = *ppos;
return ppos;
}