linux-kernel - Re: [COUNTERPATCH] mm: avoid overflowing preempt_count() in mmu_take_all

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Message-ID: <4BB480CC.2060503@redhat.com>
Date:	Thu, 01 Apr 2010 14:17:32 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	aarcange@...hat.com, akpm@...ux-foundation.org,
	Kent Overstreet <kent.overstreet@...il.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [COUNTERPATCH] mm: avoid overflowing preempt_count() in mmu_take_all_locks()

On 04/01/2010 02:13 PM, Avi Kivity wrote:
>
>> Anyway, I don't see a reason why we can't convert those locks to
>> mutexes and get rid of the whole preempt disabled region.
>
> If someone is willing to audit all code paths to make sure these locks 
> are always taken in schedulable context I agree that's a better fix.
>

 From mm/rmap.c:

> /*
>  * Lock ordering in mm:
>  *
>  * inode->i_mutex    (while writing or truncating, not reading or 
> faulting)
>  *   inode->i_alloc_sem (vmtruncate_range)
>  *   mm->mmap_sem
>  *     page->flags PG_locked (lock_page)
>  *       mapping->i_mmap_lock
>  *         anon_vma->lock
...
> *
>  * (code doesn't rely on that order so it could be switched around)
>  * ->tasklist_lock
>  *   anon_vma->lock      (memory_failure, collect_procs_anon)
>  *     pte map lock
>  */

i_mmap_lock is a spinlock, and tasklist_lock is a rwlock, so some 
changes will be needed.

-- 
error compiling committee.c: too many arguments to function

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