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>

---
 kernel/cgroup.c |   27 +++++++++++++++------------
 1 file changed, 15 insertions(+), 12 deletions(-)

Index: cgroup-2.6.25-mm1/kernel/cgroup.c
===================================================================
--- cgroup-2.6.25-mm1.orig/kernel/cgroup.c
+++ cgroup-2.6.25-mm1/kernel/cgroup.c
@@ -1440,13 +1440,6 @@ static ssize_t cgroup_common_file_write(
 	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;
@@ -2275,6 +2268,18 @@ static u64 cgroup_read_notify_on_release
 	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
  */
@@ -2291,7 +2296,7 @@ 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,
 	},
 };

--
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