[PATCH mmotm] memcg: avoid vmpressure oops when memcg disabled

[PATCH mmotm] memcg: avoid vmpressure oops when memcg disabled

[Hugh Dickins]

A CONFIG_MEMCG=y kernel booted with "cgroup_disable=memory" crashes on
a NULL memcg (but non-NULL root_mem_cgroup) when vmpressure kicks in.
Here's the patch I use to avoid that, but you might prefer a test on
mem_cgroup_disabled() somewhere.

Signed-off-by: Hugh Dickins <hughd@google.com>
---
To be folded in to
mm-memcontrol-hook-up-vmpressure-to-socket-pressure.patch
if Hannes does not prefer to fix it differently.

 mm/vmpressure.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- 4.4-next/mm/vmpressure.c	2016-01-06 10:32:21.387741753 -0800
+++ linux/mm/vmpressure.c	2016-01-06 10:48:05.956149779 -0800
@@ -260,7 +260,7 @@ void vmpressure(gfp_t gfp, struct mem_cg
 		enum vmpressure_levels level;
 
 		/* For now, no users for root-level efficiency */
-		if (memcg == root_mem_cgroup)
+		if (!memcg || memcg == root_mem_cgroup)
 			return;
 
 		spin_lock(&vmpr->sr_lock);

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Re: [PATCH mmotm] memcg: avoid vmpressure oops when memcg disabled

[Johannes Weiner]

On Sat, Jan 09, 2016 at 05:21:44PM -0800, Hugh Dickins wrote:
> A CONFIG_MEMCG=y kernel booted with "cgroup_disable=memory" crashes on
> a NULL memcg (but non-NULL root_mem_cgroup) when vmpressure kicks in.
> Here's the patch I use to avoid that, but you might prefer a test on
> mem_cgroup_disabled() somewhere.
> 
> Signed-off-by: Hugh Dickins <hughd@google.com>

Thanks Hugh. This looks good.

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

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