public inbox for linux-kernel@vger.kernel.org
 help / color / mirror / Atom feed
From: Li Zefan <lizf@cn.fujitsu.com>
To: balbir@linux.vnet.ibm.com
Cc: Zefan Li <lizf.kernel@gmail.com>,
	Xiaotian Feng <dfeng@redhat.com>,
	menage@google.com, containers@lists.linux-foundation.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] cgroup: fix reverse unlock sequence in cgroup_get_sb
Date: Wed, 22 Jul 2009 08:53:32 +0800	[thread overview]
Message-ID: <4A66630C.3030303@cn.fujitsu.com> (raw)
In-Reply-To: <20090721120106.GW24157@balbir.in.ibm.com>

>>> Seems reasonable to me. You might also want to mention that elsewhere
>>> the sequence is unlock cgroup_mutex followed by inode->i_mutex.
>>>
>>> Acked-by: Balbir Singh balbir@linux.vnet.ibm.com
>>
>> No, the unlock order is irrelevant. It's the lock order that matters. So
>> this patch
>> fixes nothing.
>>
>> Xiaotian, you didn't run into deadlock, did you?
>>
> 
> 
> Li, Consider the following
> 
> 
> lock(A)
> lock(B)
> unlock(A) 
> unlock(B)
> 
> Tomorrow if a unsuspecting programmer does this
> 
> lock(A)
> lock(B)
> unlock(A) 
> 
> code block 
> 
> unlock(B)
> 
> 
> What protects code block? lock B? Is that the intention?
> 

I won't worry about that. If unlock order is a concern,
we should have taught lockdep to detect it.

Here's a reply from Linus on this issue:

	http://lkml.org/lkml/2008/10/8/150

  parent reply	other threads:[~2009-07-22  0:55 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-07-21 10:25 [PATCH] cgroup: fix reverse unlock sequence in cgroup_get_sb Xiaotian Feng
2009-07-21 11:10 ` Balbir Singh
2009-07-21 11:12   ` Danny Feng
     [not found]   ` <8522a3d30907210438u6fce081fi835bf964d0c01e8a@mail.gmail.com>
2009-07-21 12:01     ` Balbir Singh
2009-07-21 15:34       ` Paul Menage
2009-07-21 15:47         ` Balbir Singh
2009-07-22  0:53       ` Li Zefan [this message]
2009-07-22  1:42         ` Danny Feng
2009-07-21 16:03 ` Paul Menage
2009-07-22  1:57   ` Danny Feng
2009-07-22  2:18     ` Li Zefan
2009-07-22  2:32       ` Danny Feng

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=4A66630C.3030303@cn.fujitsu.com \
    --to=lizf@cn.fujitsu.com \
    --cc=balbir@linux.vnet.ibm.com \
    --cc=containers@lists.linux-foundation.org \
    --cc=dfeng@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=lizf.kernel@gmail.com \
    --cc=menage@google.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox