From: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx> 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/20211117193932.4049412-1-gerald.schaefer@xxxxxxxxxxxxx Link: https://lkml.kernel.org/r/20211126171848.17534-1-gerald.schaefer@xxxxxxxxxxxxx Fixes: 64dd68497be7 ("mm: slub: move sysfs slab alloc/free interfaces to debugfs") Signed-off-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx> Reported-by: Steffen Maier <maier@xxxxxxxxxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Cc: Faiyaz Mohammed <faiyazm@xxxxxxxxxxxxxx> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Cc: Christoph Lameter <cl@xxxxxxxxx> Cc: Pekka Enberg <penberg@xxxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/slub.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) --- 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; } _
