cgroup files: move notify_on_release file to separate write handler

This patch moves the write handler for the cgroups notify_on_release
file into a separate handler. This handler requires no cgroups locking
since it relies on atomic bitops for synchronization.
Signed-off-by: Paul Menage <menage@google.com>
Cc: Paul Jackson <pj@sgi.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Serge Hallyn <serue@us.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/cgroup.c

@@ -1474,13 +1474,6 @@ static ssize_t cgroup_common_file_write(struct cgroup *cgrp,
 	case FILE_TASKLIST:
 		retval = attach_task_by_pid(cgrp, buffer);
 		break;
-	case FILE_NOTIFY_ON_RELEASE:
-		clear_bit(CGRP_RELEASABLE, &cgrp->flags);
-		if (simple_strtoul(buffer, NULL, 10) != 0)
-			set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
-		else
-			clear_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
-		break;
 	default:
 		retval = -EINVAL;
 		goto out2;
@@ -2252,6 +2245,18 @@ static u64 cgroup_read_notify_on_release(struct cgroup *cgrp,
 	return notify_on_release(cgrp);
 }
 
+static int cgroup_write_notify_on_release(struct cgroup *cgrp,
+					  struct cftype *cft,
+					  u64 val)
+{
+	clear_bit(CGRP_RELEASABLE, &cgrp->flags);
+	if (val)
+		set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
+	else
+		clear_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
+	return 0;
+}
+
 /*
  * for the common functions, 'private' gives the type of file
  */
@@ -2268,7 +2273,7 @@ static struct cftype files[] = {
 	{
 		.name = "notify_on_release",
 		.read_u64 = cgroup_read_notify_on_release,
-		.write = cgroup_common_file_write,
+		.write_u64 = cgroup_write_notify_on_release,
 		.private = FILE_NOTIFY_ON_RELEASE,
 	},
 };