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authorMichal Hocko <mhocko@suse.com>2016-12-02 17:26:45 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2016-12-02 18:48:03 -0800
commit20ab67a563f5299c09a234164c372aba5a59add8 (patch)
tree319ffd0791411bbe39f64941899a14ca23454cd8
parent8dc0f265d39a3933f4c1f846c7c694f12a2ab88a (diff)
downloadlinux-stericsson-20ab67a563f5299c09a234164c372aba5a59add8.tar.gz
mm: workingset: fix NULL ptr in count_shadow_nodes
Commit 0a6b76dd23fa ("mm: workingset: make shadow node shrinker memcg aware") has made the workingset shadow nodes shrinker memcg aware. The implementation is not correct though because memcg_kmem_enabled() might become true while we are doing a global reclaim when the sc->memcg might be NULL which is exactly what Marek has seen: BUG: unable to handle kernel NULL pointer dereference at 0000000000000400 IP: [<ffffffff8122d520>] mem_cgroup_node_nr_lru_pages+0x20/0x40 PGD 0 Oops: 0000 [#1] SMP CPU: 0 PID: 60 Comm: kswapd0 Tainted: G O 4.8.10-12.pvops.qubes.x86_64 #1 task: ffff880011863b00 task.stack: ffff880011868000 RIP: mem_cgroup_node_nr_lru_pages+0x20/0x40 RSP: e02b:ffff88001186bc70 EFLAGS: 00010293 RAX: 0000000000000000 RBX: ffff88001186bd20 RCX: 0000000000000002 RDX: 000000000000000c RSI: 0000000000000000 RDI: 0000000000000000 RBP: ffff88001186bc70 R08: 28f5c28f5c28f5c3 R09: 0000000000000000 R10: 0000000000006c34 R11: 0000000000000333 R12: 00000000000001f6 R13: ffffffff81c6f6a0 R14: 0000000000000000 R15: 0000000000000000 FS: 0000000000000000(0000) GS:ffff880013c00000(0000) knlGS:ffff880013d00000 CS: e033 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000400 CR3: 00000000122f2000 CR4: 0000000000042660 Call Trace: count_shadow_nodes+0x9a/0xa0 shrink_slab.part.42+0x119/0x3e0 shrink_node+0x22c/0x320 kswapd+0x32c/0x700 kthread+0xd8/0xf0 ret_from_fork+0x1f/0x40 Code: 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 3b 35 dd eb b1 00 55 48 89 e5 73 2c 89 d2 31 c9 31 c0 4c 63 ce 48 0f a3 ca 73 13 <4a> 8b b4 cf 00 04 00 00 41 89 c8 4a 03 84 c6 80 00 00 00 83 c1 RIP mem_cgroup_node_nr_lru_pages+0x20/0x40 RSP <ffff88001186bc70> CR2: 0000000000000400 ---[ end trace 100494b9edbdfc4d ]--- This patch fixes the issue by checking sc->memcg rather than memcg_kmem_enabled() which is sufficient because shrink_slab makes sure that only memcg aware shrinkers will get non-NULL memcgs and only if memcg_kmem_enabled is true. Fixes: 0a6b76dd23fa ("mm: workingset: make shadow node shrinker memcg aware") Link: http://lkml.kernel.org/r/20161201132156.21450-1-mhocko@kernel.org Signed-off-by: Michal Hocko <mhocko@suse.com> Reported-by: Marek Marczykowski-Górecki <marmarek@mimuw.edu.pl> Tested-by: Marek Marczykowski-Górecki <marmarek@mimuw.edu.pl> Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Balbir Singh <bsingharora@gmail.com> Cc: <stable@vger.kernel.org> [4.6+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/workingset.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/workingset.c b/mm/workingset.c
index 617475f529f4..fb1f9183d89a 100644
--- a/mm/workingset.c
+++ b/mm/workingset.c
@@ -348,7 +348,7 @@ static unsigned long count_shadow_nodes(struct shrinker *shrinker,
shadow_nodes = list_lru_shrink_count(&workingset_shadow_nodes, sc);
local_irq_enable();
- if (memcg_kmem_enabled()) {
+ if (sc->memcg) {
pages = mem_cgroup_node_nr_lru_pages(sc->memcg, sc->nid,
LRU_ALL_FILE);
} else {