Re: [COUNTERPATCH] mm: avoid overflowing preempt_count() in mmu_take_all_locks()

Avi Kivity
2010-04-01T16:34:23Z

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