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Commit 1c8158ee authored by Li Zefan's avatar Li Zefan Committed by Tejun Heo
Browse files

cgroup: fix umount vs cgroup_event_remove() race 



 commit 5db9a4d9
 Author: Tejun Heo <tj@kernel.org>
 Date:   Sat Jul 7 16:08:18 2012 -0700

     cgroup: fix cgroup hierarchy umount race

This commit fixed a race caused by the dput() in css_dput_fn(), but
the dput() in cgroup_event_remove() can also lead to the same BUG().

Signed-off-by: default avatarLi Zefan <lizefan@huawei.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: stable@vger.kernel.org
parent 084457f2

kernel/cgroup.c

+19 −6
Original line number Diff line number Diff line
@@ -3821,6 +3821,23 @@ static int cgroup_write_notify_on_release(struct cgroup *cgrp, 
	return 0;

}



/*

 * When dput() is called asynchronously, if umount has been done and

 * then deactivate_super() in cgroup_free_fn() kills the superblock,

 * there's a small window that vfs will see the root dentry with non-zero

 * refcnt and trigger BUG().

 *

 * That's why we hold a reference before dput() and drop it right after.

 */

static void cgroup_dput(struct cgroup *cgrp)

{

	struct super_block *sb = cgrp->root->sb;



	atomic_inc(&sb->s_active);

	dput(cgrp->dentry);

	deactivate_super(sb);

}



/*

 * Unregister event and free resources.

 *
@@ -3841,7 +3858,7 @@ static void cgroup_event_remove(struct work_struct *work) 


	eventfd_ctx_put(event->eventfd);

	kfree(event);

	dput(cgrp->dentry);

	cgroup_dput(cgrp);

}



/*
@@ -4129,12 +4146,8 @@ static void css_dput_fn(struct work_struct *work) 
{

	struct cgroup_subsys_state *css =

		container_of(work, struct cgroup_subsys_state, dput_work);

	struct dentry *dentry = css->cgroup->dentry;

	struct super_block *sb = dentry->d_sb;



	atomic_inc(&sb->s_active);

	dput(dentry);

	deactivate_super(sb);

	cgroup_dput(css->cgroup);

}



static void css_release(struct percpu_ref *ref)