From 6f6b8951897e487ea6f77b90ea01f70a9c363770 Mon Sep 17 00:00:00 2001 From: Andrey Vagin Date: Wed, 28 Aug 2013 16:35:20 -0700 Subject: [PATCH] memcg: check that kmem_cache has memcg_params before accessing it If the system had a few memory groups and all of them were destroyed, memcg_limited_groups_array_size has non-zero value, but all new caches are created without memcg_params, because memcg_kmem_enabled() returns false. We try to enumirate child caches in a few places and all of them are potentially dangerous. For example my kernel is compiled with CONFIG_SLAB and it crashed when I tryed to mount a NFS share after a few experiments with kmemcg. BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 IP: [] do_tune_cpucache+0x8a/0xd0 PGD b942a067 PUD b999f067 PMD 0 Oops: 0000 [#1] SMP Modules linked in: fscache(+) ip6table_filter ip6_tables iptable_filter ip_tables i2c_piix4 pcspkr virtio_net virtio_balloon i2c_core floppy CPU: 0 PID: 357 Comm: modprobe Not tainted 3.11.0-rc7+ #59 Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 task: ffff8800b9f98240 ti: ffff8800ba32e000 task.ti: ffff8800ba32e000 RIP: 0010:[] [] do_tune_cpucache+0x8a/0xd0 RSP: 0018:ffff8800ba32fb70 EFLAGS: 00010246 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000006 RDX: 0000000000000000 RSI: ffff8800b9f98910 RDI: 0000000000000246 RBP: ffff8800ba32fba0 R08: 0000000000000002 R09: 0000000000000004 R10: 0000000000000001 R11: 0000000000000001 R12: 0000000000000010 R13: 0000000000000008 R14: 00000000000000d0 R15: ffff8800375d0200 FS: 00007f55f1378740(0000) GS:ffff8800bfa00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b CR2: 00007f24feba57a0 CR3: 0000000037b51000 CR4: 00000000000006f0 Call Trace: enable_cpucache+0x49/0x100 setup_cpu_cache+0x215/0x280 __kmem_cache_create+0x2fa/0x450 kmem_cache_create_memcg+0x214/0x350 kmem_cache_create+0x2b/0x30 fscache_init+0x19b/0x230 [fscache] do_one_initcall+0xfa/0x1b0 load_module+0x1c41/0x26d0 SyS_finit_module+0x86/0xb0 system_call_fastpath+0x16/0x1b Signed-off-by: Andrey Vagin Cc: Pekka Enberg Cc: Christoph Lameter Cc: Glauber Costa Cc: Joonsoo Kim Cc: Michal Hocko Cc: Johannes Weiner Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/slab.h | 2 ++ 1 file changed, 2 insertions(+) diff --git a/mm/slab.h b/mm/slab.h index 620ceeddbe1a..a535033f7e9a 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -162,6 +162,8 @@ static inline const char *cache_name(struct kmem_cache *s) static inline struct kmem_cache *cache_from_memcg(struct kmem_cache *s, int idx) { + if (!s->memcg_params) + return NULL; return s->memcg_params->memcg_caches[idx]; }