]> www.pilppa.org Git - linux-2.6-omap-h63xx.git/commitdiff
cgroup: fix potential deadlock in pre_destroy
authorKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Wed, 19 Nov 2008 23:36:34 +0000 (15:36 -0800)
committerLinus Torvalds <torvalds@linux-foundation.org>
Thu, 20 Nov 2008 02:49:58 +0000 (18:49 -0800)
As Balbir pointed out, memcg's pre_destroy handler has potential deadlock.

It has following lock sequence.

cgroup_mutex (cgroup_rmdir)
    -> pre_destroy -> mem_cgroup_pre_destroy-> force_empty
-> cpu_hotplug.lock. (lru_add_drain_all->
      schedule_work->
                                      get_online_cpus)

But, cpuset has following.
cpu_hotplug.lock (call notifier)
-> cgroup_mutex. (within notifier)

Then, this lock sequence should be fixed.

Considering how pre_destroy works, it's not necessary to holding
cgroup_mutex() while calling it.

As a side effect, we don't have to wait at this mutex while memcg's
force_empty works.(it can be long when there are tons of pages.)

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
kernel/cgroup.c

index 358e77564e6f8b0b4c3964a36da48cc3051d6e73..1a06be61dcd02810fabe8c0ca40d3f60be676488 100644 (file)
@@ -2472,10 +2472,7 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
                mutex_unlock(&cgroup_mutex);
                return -EBUSY;
        }
-
-       parent = cgrp->parent;
-       root = cgrp->root;
-       sb = root->sb;
+       mutex_unlock(&cgroup_mutex);
 
        /*
         * Call pre_destroy handlers of subsys. Notify subsystems
@@ -2483,7 +2480,14 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
         */
        cgroup_call_pre_destroy(cgrp);
 
-       if (cgroup_has_css_refs(cgrp)) {
+       mutex_lock(&cgroup_mutex);
+       parent = cgrp->parent;
+       root = cgrp->root;
+       sb = root->sb;
+
+       if (atomic_read(&cgrp->count)
+           || !list_empty(&cgrp->children)
+           || cgroup_has_css_refs(cgrp)) {
                mutex_unlock(&cgroup_mutex);
                return -EBUSY;
        }