linux-kernel - [PATCH v3] staging: android/lowmemorykiller: Don't grab tasklist

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Date:	Fri, 3 Feb 2012 04:03:45 +0400
From:	Anton Vorontsov <anton.vorontsov@...aro.org>
To:	Greg KH <gregkh@...uxfoundation.org>,
	Oleg Nesterov <oleg@...hat.com>
Cc:	Arve Hjønnevåg <arve@...roid.com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	San Mehat <san@...gle.com>, Colin Cross <ccross@...roid.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-kernel@...r.kernel.org, kernel-team@...roid.com,
	linaro-kernel@...ts.linaro.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH v3] 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@...hat.com>
Signed-off-by: Anton Vorontsov <anton.vorontsov@...aro.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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