Re: [PATCH] cgroup: fix reverse unlock sequence in cgroup_get_sb

[Danny Feng]

On 07/22/2009 08:53 AM, Li Zefan wrote:
> > > > 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@xxxxxxxxxxxxxxxxxx
> > > >          
> > > 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
>    
OK, this patch is trivial. Just for consistency with previous unlock 
sequence:-)
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