[PATCH RESEND v2 1/1] fix a dead loop when in heavy low memory

From: Figo Zhang
Date: Sat Dec 26 2015 - 20:22:28 EST

Android System UI hang when run heavy monkey stress test.

V2: add more detail about how to re-produce this issue, the
important is install more than 100 apps/games.

Re-produce step:
Run this monkey stress test script with more than 100
apps/games installed:

adb shell "monkey --ignore-crashes --ignore-timeouts
--kill-process-after-error --ignore-security-exceptions
--throttle 200 -v 20000000"

kernel log:
[ 1526.272125] lowmem_scan start: 128, 213da, ofree -9849 34419, ma 529
[ 1526.272260] lowmemorykiller: select 'dTi-lm' (27289), adj 647, size 10630, to kill
[ 1526.272299] lowmem_d_timeout=4296194081
[ 1526.272303] Killing 'dTi-lm' (27289), adj 647,
[ 1526.272303] to free 42520kB on behalf of 'servicemanager' (2365) because
[ 1526.272303] cache 137676kB is below limit 221184kB for oom_score_adj 529
[ 1526.272303] Free memory is -39396kB above reserved
[ 1526.272304] lowmem_scan end: 128, 213da, return 10630
[ 1526.272710] lowmem_scan start: 128, 213da, ofree -9849 34373, ma 529
[ 1526.272832] lowmem: TIF_MEMDIE, adj=647, dTi-lm, jiffies=4296193081, 4296194081
[ 1526.274450] lowmem_scan start: 128, 280da, ofree -9601 34327, ma 529
[ 1526.274695] lowmem: TIF_MEMDIE, adj=647, dTi-lm, jiffies=4296193083, 4296194081
[ 1526.282292] lowmem_scan start: 128, 213da, ofree -9703 34327, ma 529
[ 1526.282727] lowmem: TIF_MEMDIE, adj=647, dTi-lm, jiffies=4296193090, 4296194081
[ 1526.316888] lowmem_scan start: 128, 213da, ofree -9766 34465, ma 529
[ 1526.317019] lowmem: TIF_MEMDIE, adj=647, dTi-lm, jiffies=4296193125, 4296194081
[ 1526.319311] lowmem_scan start: 128, 213da, ofree -9856 34419, ma 529
[ 1526.319442] lowmem: TIF_MEMDIE, adj=647, dTi-lm, jiffies=4296193125, 4296194081
[ 1526.322026] lowmem_scan start: 128, 280da, ofree -9841 34327, ma 529
[ 1526.360831] lowmem: TIF_MEMDIE, adj=647, dTi-lm, jiffies=4296193166, 4296194081
[ 1526.532233] lowmem_scan start: 128, 213da, ofree -9846 34511, ma 529
[ 1526.644046] lowmem_scan start: 128, 213da, ofree -9785 34235, ma 529
[ 1527.437578] lowmem: TIF_MEMDIE, adj=647, dTi-lm, jiffies=4296194246, 4296195109
[ 1527.442559] lowmem_scan start: 128, 213da, ofree -9850 41884, ma 529
[ 1527.459540] lowmem: TIF_MEMDIE, adj=647, dTi-lm, jiffies=4296194268, 4296195109
[ 1527.500352] lowmem: TIF_MEMDIE, adj=647, dTi-lm, jiffies=4296194309, 4296195109

when this happened, the android system UI will hang, no process can be
select to kill.

i found the the value of "lowmem_deathpending_timeout" will be modified
strangely, like in last killing, the value is 4296194081, but why not it
had changed to 4296195109? so it will cause the deadloop in low memory
state which will cause the android system UI hang, because no process will
be kill.

commit e5d7965f88a3 ("staging: android: lowmemorykiller: Don't wait more
than one second for a process to die") said wait 1 seconds, i think it no
need to wait 1 second, because we don't select the process with
"TIF_MEMDIE" to kill.

Signed-off-by: Figo Zhang <tianfei.zhang@xxxxxxxxx>
---
drivers/staging/android/lowmemorykiller.c | 9 ++-------
1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/drivers/staging/android/lowmemorykiller.c b/drivers/staging/android/lowmemorykiller.c
index e679d84..13c7182 100644
--- a/drivers/staging/android/lowmemorykiller.c
+++ b/drivers/staging/android/lowmemorykiller.c
@@ -59,8 +59,6 @@ static int lowmem_minfree[6] = {
};
static int lowmem_minfree_size = 4;

-static unsigned long lowmem_deathpending_timeout;
-
#define lowmem_print(level, x...) \
do { \
if (lowmem_debug_level >= (level)) \
@@ -128,11 +126,9 @@ static unsigned long lowmem_scan(struct shrinker *s, struct shrink_control *sc)
if (!p)
continue;

- if (test_tsk_thread_flag(p, TIF_MEMDIE) &&
- time_before_eq(jiffies, lowmem_deathpending_timeout)) {
+ if (test_tsk_thread_flag(p, TIF_MEMDIE)) {
task_unlock(p);
- rcu_read_unlock();
- return 0;
+ continue;
}
oom_score_adj = p->signal->oom_score_adj;
if (oom_score_adj < min_score_adj) {
@@ -170,7 +166,6 @@ static unsigned long lowmem_scan(struct shrinker *s, struct shrink_control *sc)
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;
rem += selected_tasksize;
}

--
1.7.9.5

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