[PATCH v1] mm: slub: fix the leak of alloc/free traces debugfs interface

[Faiyaz Mohammed]

fix the leak of alloc/free traces debugfs interface, reported
by kmemleak like below,

unreferenced object 0xffff00091ae1b540 (size 64):
  comm "lsbug", pid 1607, jiffies 4294958291 (age 1476.340s)
  hex dump (first 32 bytes):
    02 00 00 00 00 00 00 00 6b 6b 6b 6b 6b 6b 6b 6b  ........kkkkkkkk
    6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
  backtrace:
    [<ffff8000106b06b8>] slab_post_alloc_hook+0xa0/0x418
    [<ffff8000106b5c7c>] kmem_cache_alloc_trace+0x1e4/0x378
    [<ffff8000106b5e40>] slab_debugfs_start+0x30/0x50
    slab_debugfs_start at mm/slub.c:5831
    [<ffff8000107b3dbc>] seq_read_iter+0x214/0xd50
    [<ffff8000107b4b84>] seq_read+0x28c/0x418
    [<ffff8000109560b4>] full_proxy_read+0xdc/0x148
    [<ffff800010738f24>] vfs_read+0x104/0x340
    [<ffff800010739ee0>] ksys_read+0xf8/0x1e0
    [<ffff80001073a03c>] __arm64_sys_read+0x74/0xa8
    [<ffff8000100358d4>] invoke_syscall.constprop.0+0xdc/0x1d8
    [<ffff800010035ab4>] do_el0_svc+0xe4/0x298
    [<ffff800011138528>] el0_svc+0x20/0x30
    [<ffff800011138b08>] el0t_64_sync_handler+0xb0/0xb8
    [<ffff80001001259c>] el0t_64_sync+0x178/0x17c

Fixes: 84a2bdb1b458fc968d6d9e07dab388dc679bd747 ("mm: slub: move sysfs slab alloc/free interfaces to debugfs")
Link: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/mm/slub.c?h=next-20210617&id=84a2bdb1b458fc968d6d9e07dab388dc679bd747

Signed-off-by: Faiyaz Mohammed <faiyazm@xxxxxxxxxxxxxx>
---
 mm/slub.c | 17 +++++------------
 1 file changed, 5 insertions(+), 12 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index fcb0c50..f006766 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -5785,31 +5785,24 @@ static int slab_debugfs_show(struct seq_file *seq, void *v)
 
 static void slab_debugfs_stop(struct seq_file *seq, void *v)
 {
-	kfree(v);
 }
 
 static void *slab_debugfs_next(struct seq_file *seq, void *v, loff_t *ppos)
 {
-	loff_t *spos = v;
 	struct loc_track *t = seq->private;
 
+	v = ppos;
 	if (*ppos < t->count) {
-		*ppos = ++*spos;
-		return spos;
+		++*ppos;
+		return v;
 	}
-	*ppos = ++*spos;
+	++*ppos;
 	return NULL;
 }
 
 static void *slab_debugfs_start(struct seq_file *seq, loff_t *ppos)
 {
-	loff_t *spos = kmalloc(sizeof(loff_t), GFP_KERNEL);
-
-	if (!spos)
-		return NULL;
-
-	*spos = *ppos;
-	return spos;
+	return ppos;
 }
 
 static const struct seq_operations slab_debugfs_sops = {
-- 
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