[PATCH] Reduce cpuset.c write_lock_irq() to read_lock()

[Paul Menage <menage@google.com>]

cpuset.c:update_nodemask() uses a write_lock_irq() on tasklist_lock to
block concurrent forks; a read_lock() suffices and is less intrusive.

Signed-off-by: Paul Menage<menage@google.com>

---
 kernel/cpuset.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Index: scratch-2.6.22-rc1-mm1/kernel/cpuset.c
===================================================================
--- scratch-2.6.22-rc1-mm1.orig/kernel/cpuset.c
+++ scratch-2.6.22-rc1-mm1/kernel/cpuset.c
@@ -923,10 +923,10 @@ static int update_nodemask(struct cpuset
 		mmarray = kmalloc(ntasks * sizeof(*mmarray), GFP_KERNEL);
 		if (!mmarray)
 			goto done;
-		write_lock_irq(&tasklist_lock);		/* block fork */
+		read_lock(&tasklist_lock);		/* block fork */
 		if (atomic_read(&cs->count) <= ntasks)
 			break;				/* got enough */
-		write_unlock_irq(&tasklist_lock);	/* try again */
+		read_unlock(&tasklist_lock);	/* try again */
 		kfree(mmarray);
 	}
 
@@ -948,7 +948,7 @@ static int update_nodemask(struct cpuset
 			continue;
 		mmarray[n++] = mm;
 	} while_each_thread(g, p);
-	write_unlock_irq(&tasklist_lock);
+	read_unlock(&tasklist_lock);
 
 	/*
 	 * Now that we've dropped the tasklist spinlock, we can