Re: [PATCH 2/2] android, lmk: Reverse the order of setting TIF_MEMDIE and sending SIGKILL.

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

Greg KH wrote:
> On Fri, Sep 04, 2015 at 04:05:59PM +0200, Michal Hocko wrote:
> > On Wed 02-09-15 18:06:20, Greg KH wrote:
> > [...]
> > > And if we aren't taking patch 1/2, I guess this one isn't needed either?
> > 
> > Unlike the patch1 which was pretty much cosmetic this fixes a real
> > issue.
> 
> Ok, then it would be great to get this in a format that I can apply it
> in :)

I see. Here is a minimal patch.
(Acked-by: from http://lkml.kernel.org/r/20150827084443.GE14367@dhcp22.suse.cz )
----------------------------------------
>From 118609fa25700af11791b1b7e8349f8973a9e7e4 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Sat, 5 Sep 2015 02:58:12 +0900
Subject: [PATCH] android, lmk: Send SIGKILL before setting TIF_MEMDIE.

It was observed that setting TIF_MEMDIE before sending SIGKILL at
oom_kill_process() allows memory reserves to be depleted by allocations
which are not needed for terminating the OOM victim.

This patch reverts commit 6bc2b856bb7c ("staging: android: lowmemorykiller:
set TIF_MEMDIE before send kill sig"), for oom_kill_process() was updated
to send SIGKILL before setting TIF_MEMDIE.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: Michal Hocko <mhocko@suse.com>
---
 drivers/staging/android/lowmemorykiller.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/drivers/staging/android/lowmemorykiller.c b/drivers/staging/android/lowmemorykiller.c
index 872bd60..569d12c 100644
--- a/drivers/staging/android/lowmemorykiller.c
+++ b/drivers/staging/android/lowmemorykiller.c
@@ -157,26 +157,22 @@ static unsigned long lowmem_scan(struct shrinker *s, struct shrink_control *sc)
 	}
 	if (selected) {
 		task_lock(selected);
-		if (!selected->mm) {
-			/* Already exited, cannot do mark_tsk_oom_victim() */
-			task_unlock(selected);
-			goto out;
-		}
+		send_sig(SIGKILL, selected, 0);
 		/*
 		 * FIXME: lowmemorykiller shouldn't abuse global OOM killer
 		 * infrastructure. There is no real reason why the selected
 		 * task should have access to the memory reserves.
 		 */
-		mark_oom_victim(selected);
+		if (selected->mm)
+			mark_oom_victim(selected);
 		task_unlock(selected);
 		lowmem_print(1, "send sigkill to %d (%s), adj %hd, size %d\n",
 			     selected->pid, selected->comm,
 			     selected_oom_score_adj, selected_tasksize);
 		lowmem_deathpending_timeout = jiffies + HZ;
-		send_sig(SIGKILL, selected, 0);
 		rem += selected_tasksize;
 	}
-out:
+
 	lowmem_print(4, "lowmem_scan %lu, %x, return %lu\n",
 		     sc->nr_to_scan, sc->gfp_mask, rem);
 	rcu_read_unlock();
-- 
1.8.3.1

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