Re: [BUGFIX][PATCH] memcg: fix deadlock between lock_page_cgroupand mapping tree_lock

[Balbir Singh <balbir@linux.vnet.ibm.com>]

* Andrew Morton <akpm@linux-foundation.org> [2009-05-13 11:56:26]:

> On Wed, 13 May 2009 13:30:31 +0900
> Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
> 
> > mapping->tree_lock can be aquired from interrupt context.
> > Then, following dead lock can occur.
> > 
> > Assume "A" as a page.
> > 
> >  CPU0:
> >        lock_page_cgroup(A)
> > 		interrupted
> > 			-> take mapping->tree_lock.
> >  CPU1:
> >        take mapping->tree_lock
> > 		-> lock_page_cgroup(A)
> 
> And we didn't find out about this because lock_page_cgroup() uses
> bit_spin_lock(), and lockdep doesn't handle bit_spin_lock().
> 
> It would perhaps be useful if one of you guys were to add a spinlock to
> struct page, convert lock_page_cgroup() to use that spinlock then run a
> full set of tests under lockdep, see if it can shake out any other bugs.
>

May be under DEBUG_VM we could do that. Good suggestion! 

-- 
	Balbir

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