linux-kernel - Re: [PATCH v2 6/6] cgroup: remove bogus comments in cgroup

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Message-ID: <5101ED8C.9030205@huawei.com>
Date:	Fri, 25 Jan 2013 10:27:24 +0800
From:	Li Zefan <lizefan@...wei.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Cgroups <cgroups@...r.kernel.org>
Subject: Re: [PATCH v2 6/6] cgroup: remove bogus comments in cgroup_diput()

> On Thu, Jan 24, 2013 at 02:32:02PM +0800, Li Zefan wrote:
>> Since commit 48ddbe194623ae089cc0576e60363f2d2e85662a
>> ("cgroup: make css->refcnt clearing on cgroup removal optional"),
>> each css holds a ref on cgroup's dentry, so cgroup_diput() won't be
>> called until all css' refs go down to 0, which invalids the comments.
>>
>> Signed-off-by: Li Zefan <lizefan@...wei.com>
>> ---
>>  kernel/cgroup.c | 6 ------
>>  1 file changed, 6 deletions(-)
>>
>> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
>> index f18b0d9..368cff1 100644
>> --- a/kernel/cgroup.c
>> +++ b/kernel/cgroup.c
>> @@ -899,12 +899,6 @@ static void cgroup_diput(struct dentry *dentry, struct inode *inode)
>>  		struct cgroup *cgrp = dentry->d_fsdata;
>>  
>>  		BUG_ON(!(cgroup_is_removed(cgrp)));
>> -		/* It's possible for external users to be holding css
>> -		 * reference counts on a cgroup; css_put() needs to
>> -		 * be able to access the cgroup after decrementing
>> -		 * the reference count in order to know if it needs to
>> -		 * queue the cgroup to be handled by the release
>> -		 * agent */
> 
> The latter half is still true tho.  I applied the patch anyway as the
> comment isn't all that useful without covering everything intended to
> be covered with RCU.  Can you please write up another patch
> documenting what's covered by RCU (stuff that we intend to keep
> guaranteeing to be safe to access only w/ RCU)?
> 

Sure. I'll try.

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