[PATCH RT 25/36] scheduling while atomic in cgroup code

From: Steven Rostedt
Date: Thu Mar 12 2015 - 15:27:15 EST

3.12.38-rt53-rc1 stable review patch.
If anyone has any objections, please let me know.


From: Mike Galbraith <umgwanakikbuti@xxxxxxxxx>

mm, memcg: make refill_stock() use get_cpu_light()

Nikita reported the following memcg scheduling while atomic bug:

Call Trace:
[e22d5a90] [c0007ea8] show_stack+0x4c/0x168 (unreliable)
[e22d5ad0] [c0618c04] __schedule_bug+0x94/0xb0
[e22d5ae0] [c060b9ec] __schedule+0x530/0x550
[e22d5bf0] [c060bacc] schedule+0x30/0xbc
[e22d5c00] [c060ca24] rt_spin_lock_slowlock+0x180/0x27c
[e22d5c70] [c00b39dc] res_counter_uncharge_until+0x40/0xc4
[e22d5ca0] [c013ca88] drain_stock.isra.20+0x54/0x98
[e22d5cc0] [c01402ac] __mem_cgroup_try_charge+0x2e8/0xbac
[e22d5d70] [c01410d4] mem_cgroup_charge_common+0x3c/0x70
[e22d5d90] [c0117284] __do_fault+0x38c/0x510
[e22d5df0] [c011a5f4] handle_pte_fault+0x98/0x858
[e22d5e50] [c060ed08] do_page_fault+0x42c/0x6fc
[e22d5f40] [c000f5b4] handle_page_fault+0xc/0x80

What happens:

spin_lock() <== boom

Fix it by replacing get/put_cpu_var() with get/put_cpu_light().

Cc: stable-rt@xxxxxxxxxxxxxxx
Reported-by: Nikita Yushchenko <nyushchenko@xxxxxxxxxxxxx>
Signed-off-by: Mike Galbraith <umgwanakikbuti@xxxxxxxxx>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
mm/memcontrol.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 003521e47622..ba7a8ae06476 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2474,14 +2474,17 @@ static void __init memcg_stock_init(void)
static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
- struct memcg_stock_pcp *stock = &get_cpu_var(memcg_stock);
+ struct memcg_stock_pcp *stock;
+ int cpu = get_cpu_light();
+ stock = &per_cpu(memcg_stock, cpu);

if (stock->cached != memcg) { /* reset if necessary */
stock->cached = memcg;
stock->nr_pages += nr_pages;
- put_cpu_var(memcg_stock);
+ put_cpu_light();


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