ChangeSet@1.1136.78.2  2003-12-07 12:43:34-02:00  wli at holomorphy.com
[PATCH] out_of_memory() locking

On Sun, Nov 30, 2003 at 08:18:02AM -0800, William Lee Irwin III wrote:
> (1) the timestamps/etc. weren't locked, and when cpus raced, it caused
>  false OOM kills
> (2) the mm could go away while scanning the tasklist, causing the thing
>  to try to kill kernel threads
> Here's a preliminary backport (please do _NOT_ apply until I or someone
> tests it) for you to comment on. Basically, do you want (1) and (2)
> split out, is the basic thing okay, etc.?

out_of_memory()'s operational variables are not locked, and can be
reset by multiple cpus simultaneously, causing false OOM kills.

This patch adds an oom_lock to out_of_memory() to protect its operational
variables.


-- wli



--- linux-2.4.23/mm/oom_kill.c.orig	Tue Dec  9 00:20:47 2003
+++ linux-2.4.23/mm/oom_kill.c	Tue Dec  9 00:24:20 2003
@@ -202,6 +202,11 @@
  */
 void out_of_memory(void)
 {
+	/*
+	* oom_lock protects out_of_memory()'s static variables.
+	* It's a global lock; this is not performance-critical.
+	*/
+	static spinlock_t oom_lock = SPIN_LOCK_UNLOCKED;
 	static unsigned long first, last, count, lastkill;
 	unsigned long now, since;
 
@@ -211,6 +216,7 @@
 	if (nr_swap_pages > 0)
 		return;
 
+	spin_lock(&oom_lock);
 	now = jiffies;
 	since = now - last;
 	last = now;
@@ -229,14 +235,14 @@
 	 */
 	since = now - first;
 	if (since < HZ)
-		return;
+		goto out_unlock;
 
 	/*
 	 * If we have gotten only a few failures,
 	 * we're not really oom. 
 	 */
 	if (++count < 10)
-		return;
+		goto out_unlock;
 
 	/*
 	 * If we just killed a process, wait a while
@@ -245,17 +251,25 @@
 	 */
 	since = now - lastkill;
 	if (since < HZ*5)
-		return;
+		goto out_unlock;
 
 	/*
 	 * Ok, really out of memory. Kill something.
 	 */
 	lastkill = now;
+	
+	/* oom_kill() can sleep */
+	spin_unlock(&oom_lock);
 	oom_kill();
+	spin_lock(&oom_lock);
 
 reset:
-	first = now;
+	if (first < now)
+		first = now;
 	count = 0;
+
+out_unlock:
+	spin_unlock(&oom_lock);
 }
 
 #endif	/* Unused file */