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>]

Reposting updated version as it turned out that we can call do_send_sig_info()
with task_lock held. ;-) ( http://marc.info/?l=linux-mm&m=144059948628905&w=2 )

Tetsuo Handa wrote:
> Should selected_tasksize be added to rem even when TIF_MEMDIE was not set?
Commit e1099a69a624 "android, lmk: avoid setting TIF_MEMDIE if process
has already exited" changed not to add selected_tasksize to rem. But I
noticed that rem is initialized to 0 and there is only one addition
(i.e. rem += selected_tasksize means rem = selected_tasksize) since
commit 7dc19d5affd7 "drivers: convert shrinkers to new count/scan API".
I don't know what values we should return, but this patch restores
pre commit e1099a69a624 because omitting a call to mark_oom_victim()
due to race will not prevent from reclaiming memory because we already
sent SIGKILL.
------------------------------------------------------------
>From b7075abd3a1e903e88f1755c68adc017d2125b0d Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Thu, 27 Aug 2015 00:13:57 +0900
Subject: [PATCH 2/2] 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>
---
 drivers/staging/android/lowmemorykiller.c | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/drivers/staging/android/lowmemorykiller.c b/drivers/staging/android/lowmemorykiller.c
index d5d25e4..af604cf 100644
--- a/drivers/staging/android/lowmemorykiller.c
+++ b/drivers/staging/android/lowmemorykiller.c
@@ -156,26 +156,21 @@ next:
 	}
 	if (selected) {
 		task_lock(selected);
-		if (!selected->mm) {
-			/* Already exited, cannot do mark_tsk_oom_victim() */
-			task_unlock(selected);
-			goto out;
-		}
+		lowmem_print(1, "send sigkill to %d (%s), adj %hd, size %d\n",
+			     selected->pid, selected->comm,
+			     selected_oom_score_adj, selected_tasksize);
+		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);
-		lowmem_print(1, "send sigkill to %d (%s), adj %hd, size %d\n",
-			     selected->pid, selected->comm,
-			     selected_oom_score_adj, selected_tasksize);
+		if (selected->mm)
+			mark_oom_victim(selected);
 		task_unlock(selected);
 		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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