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SubjectRe: [BUGFIX][PATCH] memcg: fix deadlock between lock_page_cgroup and mapping tree_lock
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.



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