linux-kernel - [PATCH] mm: slub: remove dead and buggy code from sysfs_slab

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Date:   Fri, 30 Sep 2022 10:47:42 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] mm: slub: remove dead and buggy code from sysfs_slab_add()

The function sysfs_slab_add() has two callers:

One is slab_sysfs_init(), which first initializes slab_kset, and only
when that succeeds sets slab_state to FULL, and then proceeds to call
sysfs_slab_add() for all previously created slabs.

The other is __kmem_cache_create(), but only after a

	if (slab_state <= UP)
		return 0;

check.

So in other words, sysfs_slab_add() is never called without
slab_kset (aka the return value of cache_kset()) being non-NULL.

And this is just as well, because if we ever did take this path and
called kobject_init(&s->kobj), and then later when called again from
slab_sysfs_init() would end up calling kobject_init_and_add(), we
would hit

	if (kobj->state_initialized) {
		/* do not error out as sometimes we can recover */
		pr_err("kobject (%p): tried to init an initialized object, something is seriously wrong.\n",
		dump_stack();
	}

in kobject.c.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
 mm/slub.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 4b98dff9be8e..04a7f75a7b1f 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -5937,11 +5937,6 @@ static int sysfs_slab_add(struct kmem_cache *s)
 	struct kset *kset = cache_kset(s);
 	int unmergeable = slab_unmergeable(s);
 
-	if (!kset) {
-		kobject_init(&s->kobj, &slab_ktype);
-		return 0;
-	}
-
 	if (!unmergeable && disable_higher_order_debug &&
 			(slub_debug & DEBUG_METADATA_FLAGS))
 		unmergeable = 1;
-- 
2.37.2