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

[Andrew Morton]

On Wed, 13 May 2009 13:30:31 +0900
Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx> 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.

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