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[021/146] mm/slab_common: use WARN() if cache still has objects on destroy

Message ID 20220114220358.-PVz8K_7b%akpm@linux-foundation.org (mailing list archive)
State New
Headers show
Series [001/146] kthread: add the helper function kthread_run_on_cpu() | expand

Commit Message

Andrew Morton Jan. 14, 2022, 10:03 p.m. UTC 
From: Marco Elver <elver@google.com>
Subject: mm/slab_common: use WARN() if cache still has objects on destroy

Calling kmem_cache_destroy() while the cache still has objects allocated
is a kernel bug, and will usually result in the entire cache being leaked.
While the message in kmem_cache_destroy() resembles a warning, it is
currently not implemented using a real WARN().

This is problematic for infrastructure testing the kernel, all of which
rely on the specific format of WARN()s to pick up on bugs.

Some 13 years ago this used to be a simple WARN_ON() in slub, but
d629d8195793 ("slub: improve kmem_cache_destroy() error message") changed
it into an open-coded warning to avoid confusion with a bug in slub
itself.

Instead, turn the open-coded warning into a real WARN() with the message
preserved, so that test systems can actually identify these issues, and we
get all the other benefits of using a normal WARN().  The warning message
is extended with "when called from <caller-ip>" to make it even clearer
where the fault lies.

For most configurations this is only a cosmetic change, however, note that
WARN() here will now also respect panic_on_warn.

Link: https://lkml.kernel.org/r/20211102170733.648216-1-elver@google.com
Signed-off-by: Marco Elver <elver@google.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/slab_common.c |   11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)
diff mbox series

Patch

--- a/mm/slab_common.c~mm-slab_common-use-warn-if-cache-still-has-objects-on-destroy
+++ a/mm/slab_common.c
@@ -489,8 +489,6 @@  void slab_kmem_cache_release(struct kmem
 
 void kmem_cache_destroy(struct kmem_cache *s)
 {
-	int err;
-
 	if (unlikely(!s))
 		return;
 
@@ -501,12 +499,9 @@  void kmem_cache_destroy(struct kmem_cach
 	if (s->refcount)
 		goto out_unlock;
 
-	err = shutdown_cache(s);
-	if (err) {
-		pr_err("%s %s: Slab cache still has objects\n",
-		       __func__, s->name);
-		dump_stack();
-	}
+	WARN(shutdown_cache(s),
+	     "%s %s: Slab cache still has objects when called from %pS",
+	     __func__, s->name, (void *)_RET_IP_);
 out_unlock:
 	mutex_unlock(&slab_mutex);
 	cpus_read_unlock();