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

[Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>]

Otherwise, 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

fixes: slub-never-fail-to-shrink-cache
Signed-off-by: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
Reported-by: Huang Ying <ying.huang@xxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
---
 mm/slub.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/slub.c b/mm/slub.c
index 0909e13cf708..59dde3f3efed 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3499,6 +3499,8 @@ int __kmem_cache_shrink(struct kmem_cache *s, bool deactivate)
 		list_for_each_entry_safe(page, t, &discard, lru)
 			discard_slab(s, page);
 
+		INIT_LIST_HEAD(&discard);
+
 		if (slabs_node(s, node))
 			ret = 1;
 	}
-- 
1.7.10.4

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