linux-kernel - Re: [PATCH 2/2] cgroup: make css->refcnt clearing on cgroup removal optional

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Message-ID: <20120523222242.GD3933@htj.dyndns.org>
Date:	Wed, 23 May 2012 15:22:42 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Sasha Levin <levinsasha928@...il.com>
Cc:	Li Zefan <lizefan@...wei.com>,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org, fweisbec@...il.com, rni@...gle.com,
	ctalbott@...gle.com, Vivek Goyal <vgoyal@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Balbir Singh <bsingharora@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH 2/2] cgroup: make css->refcnt clearing on cgroup removal
 optional

Hello, Sasha.

Does the following patch fix the problem you're seeing?

Thanks.

---
 kernel/cgroup.c |   17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index ad8eae5..7cf9669 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -896,10 +896,13 @@ static void cgroup_diput(struct dentry *dentry, struct inode *inode)
 		mutex_unlock(&cgroup_mutex);
 
 		/*
-		 * Drop the active superblock reference that we took when we
-		 * created the cgroup
+		 * We want to drop the active superblock reference that we
+		 * took when we created the cgroup after all dentry refs
+		 * are gone - kill_sb gets mighty unhappy otherwise.  Set
+		 * dentry->d_fsdata to cgroup_diput() to tell
+		 * cgroup_d_release() to call deactivate_super().
 		 */
-		deactivate_super(cgrp->root->sb);
+		dentry->d_fsdata = cgroup_diput;
 
 		/*
 		 * if we're getting rid of the cgroup, refcount should ensure
@@ -925,6 +928,13 @@ static int cgroup_delete(const struct dentry *d)
 	return 1;
 }
 
+static void cgroup_d_release(struct dentry *dentry)
+{
+	/* did cgroup_diput() tell me to deactivate super? */
+	if (dentry->d_fsdata == cgroup_diput)
+		deactivate_super(dentry->d_sb);
+}
+
 static void remove_dir(struct dentry *d)
 {
 	struct dentry *parent = dget(d->d_parent);
@@ -1532,6 +1542,7 @@ static int cgroup_get_rootdir(struct super_block *sb)
 	static const struct dentry_operations cgroup_dops = {
 		.d_iput = cgroup_diput,
 		.d_delete = cgroup_delete,
+		.d_release = cgroup_d_release,
 	};
 
 	struct inode *inode =
--
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