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/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>

diff --git a/mm/slub.c b/mm/slub.c
index a862682..abe7db5 100644 (file)
--- a/mm/slub.c
+++ b/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 seq_file *seq, void *v, loff_t *ppos)
 {
        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;
 }