linux-kernel - Re: [PATCH -mm] slub: kmem_cache_shrink: init discard list after freeing slabs

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Date:	Wed, 11 Feb 2015 18:41:28 +0300
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Christoph Lameter <cl@...ux.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>, Huang Ying <ying.huang@...el.com>,
	"Pekka Enberg" <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	"Joonsoo Kim" <iamjoonsoo.kim@....com>
Subject: Re: [PATCH -mm] slub: kmem_cache_shrink: init discard list after
 freeing slabs

On Wed, Feb 11, 2015 at 09:00:39AM -0600, Christoph Lameter wrote:
> Hmmmm... Thinking about this some more. It may be better to initialize the
> list head at the beginning of the loop?
> 
> Also the promote array should also be initialized in the loop right?

I do initialize promote lists in the loop using list_splice_init, but
yeah, initializing them in the beginning of the loop would look more
readable indeed. The updated patch is below. Thanks!
---
From: Vladimir Davydov <vdavydov@...allels.com>
Subject: [PATCH] slub: kmem_cache_shrink: fix crash due to uninitialized
 discard list

Currently, the discard list is only initialized at the beginning of the
function. As a result, if there are > 1 nodes, we can get use-after-free
while processing the second or higher node:

    WARNING: CPU: 60 PID: 1 at lib/list_debug.c:29 __list_add+0x3c/0xa9()
    list_add corruption. next->prev should be prev (ffff881ff0a6bb98), but was ffffea007ff57020. (next=ffffea007fbf7320).
    Modules linked in:
    CPU: 60 PID: 1 Comm: swapper/0 Not tainted 3.19.0-rc7-next-20150203-gb50cadf #2178
    Hardware name: Intel Corporation BRICKLAND/BRICKLAND, BIOS BIVTSDP1.86B.0038.R02.1307231126 07/23/2013
     0000000000000009 ffff881ff0a6ba88 ffffffff81c2e096 ffffffff810e2d03
     ffff881ff0a6bad8 ffff881ff0a6bac8 ffffffff8108b320 ffff881ff0a6bb18
     ffffffff8154bbc7 ffff881ff0a6bb98 ffffea007fbf7320 ffffea00ffc3c220
    Call Trace:
     [<ffffffff81c2e096>] dump_stack+0x4c/0x65
     [<ffffffff810e2d03>] ? console_unlock+0x398/0x3c7
     [<ffffffff8108b320>] warn_slowpath_common+0xa1/0xbb
     [<ffffffff8154bbc7>] ? __list_add+0x3c/0xa9
     [<ffffffff8108b380>] warn_slowpath_fmt+0x46/0x48
     [<ffffffff8154bbc7>] __list_add+0x3c/0xa9
     [<ffffffff811bf5aa>] __kmem_cache_shrink+0x12b/0x24c
     [<ffffffff81190ca9>] kmem_cache_shrink+0x26/0x38
     [<ffffffff815848b4>] acpi_os_purge_cache+0xe/0x12
     [<ffffffff815c6424>] acpi_purge_cached_objects+0x32/0x7a
     [<ffffffff825f70f1>] acpi_initialize_objects+0x17e/0x1ae
     [<ffffffff825f5177>] ? acpi_sleep_proc_init+0x2a/0x2a
     [<ffffffff825f5209>] acpi_init+0x92/0x25e
     [<ffffffff810002bd>] ? do_one_initcall+0x90/0x17f
     [<ffffffff811bdfcd>] ? kfree+0x1fc/0x2d5
     [<ffffffff825f5177>] ? acpi_sleep_proc_init+0x2a/0x2a
     [<ffffffff8100031a>] do_one_initcall+0xed/0x17f
     [<ffffffff825ae0e2>] kernel_init_freeable+0x1f0/0x278
     [<ffffffff81c1f31a>] ? rest_init+0x13e/0x13e
     [<ffffffff81c1f328>] kernel_init+0xe/0xda
     [<ffffffff81c3ca7c>] ret_from_fork+0x7c/0xb0
     [<ffffffff81c1f31a>] ? rest_init+0x13e/0x13e

Fix this by initializing the discard list at each iteration of the
for_each_kmem_cache_node loop. Also, move promote lists initialization
to the beginning of the loop to conform.

fixes: slub-never-fail-to-shrink-cache
Signed-off-by: Vladimir Davydov <vdavydov@...allels.com>
Reported-by: Huang Ying <ying.huang@...el.com>
Cc: Christoph Lameter <cl@...ux.com>
Cc: Pekka Enberg <penberg@...nel.org>
Cc: David Rientjes <rientjes@...gle.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@....com>

diff --git a/mm/slub.c b/mm/slub.c
index 0909e13cf708..6832c4eab104 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3437,7 +3437,7 @@ int __kmem_cache_shrink(struct kmem_cache *s, bool deactivate)
 	struct kmem_cache_node *n;
 	struct page *page;
 	struct page *t;
-	LIST_HEAD(discard);
+	struct list_head discard;
 	struct list_head promote[SHRINK_PROMOTE_MAX];
 	unsigned long flags;
 	int ret = 0;
@@ -3457,11 +3457,12 @@ int __kmem_cache_shrink(struct kmem_cache *s, bool deactivate)
 		kick_all_cpus_sync();
 	}
 
-	for (i = 0; i < SHRINK_PROMOTE_MAX; i++)
-		INIT_LIST_HEAD(promote + i);
-
 	flush_all(s);
 	for_each_kmem_cache_node(s, node, n) {
+		INIT_LIST_HEAD(&discard);
+		for (i = 0; i < SHRINK_PROMOTE_MAX; i++)
+			INIT_LIST_HEAD(promote + i);
+
 		spin_lock_irqsave(&n->list_lock, flags);
 
 		/*
@@ -3491,7 +3492,7 @@ int __kmem_cache_shrink(struct kmem_cache *s, bool deactivate)
 		 * partial list.
 		 */
 		for (i = SHRINK_PROMOTE_MAX - 1; i >= 0; i--)
-			list_splice_init(promote + i, &n->partial);
+			list_splice(promote + i, &n->partial);
 
 		spin_unlock_irqrestore(&n->list_lock, flags);
 
--
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