[18/21] mm/slub: fix endianness bug for alloc/free_traces attributes

Commit Message

Andrew Morton Dec. 10, 2021, 10:47 p.m. UTC

From: Gerald Schaefer <[e-mail]>
Subject: mm/slub: fix endianness bug for alloc/free_traces attributes

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/[e-mail]
Link: https://lkml.kernel.org/r/[e-mail]
Fixes: 64dd68497be7 ("mm: slub: move sysfs slab alloc/free interfaces to debugfs")
Signed-off-by: Gerald Schaefer <[e-mail]>
Reported-by: Steffen Maier <[e-mail]>
Acked-by: Vlastimil Babka <[e-mail]>
Cc: Faiyaz Mohammed <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Christoph Lameter <[e-mail]>
Cc: Pekka Enberg <[e-mail]>
Cc: David Rientjes <[e-mail]>
Cc: Joonsoo Kim <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/slub.c |   15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

Patch

--- a/mm/slub.c~mm-slub-fix-endianness-bug-for-alloc-free_traces-attributes
+++ a/mm/slub.c
@@ -5081,6 +5081,7 @@  struct loc_track {
 	unsigned long max;
 	unsigned long count;
 	struct location *loc;
+	loff_t idx;
 };
 
 static struct dentry *slab_debugfs_root;
@@ -6052,11 +6053,11 @@  __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];
 
@@ -6105,16 +6106,18 @@  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;
 }