On 11/26/21 18:18, Gerald Schaefer wrote: > 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 > 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> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> With a nit below: > --- > mm/slub.c | 15 +++++++++------ > 1 file changed, 9 insertions(+), 6 deletions(-) > > diff --git a/mm/slub.c b/mm/slub.c > index a8626825a829..abe7db581d68 100644 > --- 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; What I had in mind, and to be more in line with the seq_file example, would be to return &t->idx here. Then it's what gets passed to slab_debugfs_show() as 'v'. But since we ignore 'v' there, it probably doesn't matter. > > 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; And same here. > } > >
