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Subject[PATCH 3/6] staging: android/lowmemorykiller: Don't grab tasklist_lock
Grabbing tasklist_lock has its disadvantages, i.e. it blocks
process creation and destruction. If there are lots of processes,
blocking doesn't sound as a great idea.

For LMK, it is sufficient to surround tasks list traverse with
rcu_read_{,un}lock().
From now on using force_sig() is not safe, as it can race with an
already exiting task, so we use send_sig() now. As a downside, it
won't kill PID namespace init processes, but that's not what we
want anyway.

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
drivers/staging/android/lowmemorykiller.c | 7 ++++---
1 files changed, 4 insertions(+), 3 deletions(-)
diff --git a/drivers/staging/android/lowmemorykiller.c b/drivers/staging/android/lowmemorykiller.c
index 2d8d2b7..63da844 100644
--- a/drivers/staging/android/lowmemorykiller.c
+++ b/drivers/staging/android/lowmemorykiller.c
@@ -34,6 +34,7 @@
#include <linux/mm.h>
#include <linux/oom.h>
#include <linux/sched.h>
+#include <linux/rcupdate.h>
#include <linux/profile.h>
#include <linux/notifier.h>

@@ -132,7 +133,7 @@ static int lowmem_shrink(struct shrinker *s, struct shrink_control *sc)
}
selected_oom_adj = min_adj;

- read_lock(&tasklist_lock);
+ rcu_read_lock();
for_each_process(p) {
struct mm_struct *mm;
struct signal_struct *sig;
@@ -180,12 +181,12 @@ static int lowmem_shrink(struct shrinker *s, struct shrink_control *sc)
lowmem_deathpending = selected;
task_handoff_register(&task_nb);
#endif
- force_sig(SIGKILL, selected);
+ send_sig(SIGKILL, selected, 0);
rem -= selected_tasksize;
}
lowmem_print(4, "lowmem_shrink %lu, %x, return %d\n",
sc->nr_to_scan, sc->gfp_mask, rem);
- read_unlock(&tasklist_lock);
+ rcu_read_unlock();
return rem;
}

--
1.7.7.6


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