linux-kernel - Re: 3.5-rc3: BUG: Dentry still in use (1) [unmount of cgroup cgroup]

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Message-ID: <20120703171033.GC555@google.com>
Date:	Tue, 3 Jul 2012 10:10:33 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Li Zefan <lizefan@...wei.com>, shyju pv <shyju.pv@...wei.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
	Sanil kumar <sanil.kumar@...wei.com>,
	Masanari Iida <standby24x7@...il.com>
Subject: Re: 3.5-rc3: BUG: Dentry still in use (1) [unmount of cgroup
 cgroup]

Hello, Al.

On Sat, Jun 30, 2012 at 09:34:21AM +0100, Al Viro wrote:
> Now that I've looked at that code again...  What's the story with
>                 simple_unlink(d->d_inode, d);
> in cgroup_rm_file()?  Wrong parent inode, at the very least...

Yeah, indeed.  My mistake while refactoring the code.  Will fix.

> While we are at it, what the hell is going on in
> static void cgroup_clear_directory(struct dentry *dir)
> {
>         struct cgroup *cgrp = __d_cgrp(dir);
> 
>         while (!list_empty(&cgrp->files))
>                 cgroup_rm_file(cgrp, NULL);
> }
> Are you fighting some kind of race against somebody adding stuff
> there?  Unless I'm seriously misreading cgroup_rm_file(), it'll
> do all the work on the first call...

cgroup_rm_file() finds the file matching @cft, deletes that one file
and returns.  Passing in %NULL @cft makes it deletes the first file
but it still returns after deleting one.  Maybe breaking up
list_for_each_entry() so that deletion and returning is outside the
loop would make that clearer.

Thanks.

-- 
tejun
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