Re: [PATCH 01 of 11] mmu-notifier-core

[Jack Steiner]

On Fri, May 02, 2008 at 05:05:04PM +0200, Andrea Arcangeli wrote:
> # HG changeset patch
> # User Andrea Arcangeli <andrea@xxxxxxxxxxxx>
> # Date 1209740175 -7200
> # Node ID 1489529e7b53d3f2dab8431372aa4850ec821caa
> # Parent  5026689a3bc323a26d33ad882c34c4c9c9a3ecd8
> mmu-notifier-core
 


I upgraded to the latest mmu notifier patch & hit a deadlock. (Sorry -
I should have seen this  earlier but I haven't tracked the last couple
of patches).

The GRU does the registration/deregistration of mmu notifiers from mmap/munmap.
At this point, the mmap_sem is already held writeable. I hit a deadlock
in mm_lock.

A quick fix would be to do one of the following:

	- move the mmap_sem locking to the caller of the [de]registration routines.
	  Since the first/last thing done in mm_lock/mm_unlock is to
	  acquire/release mmap_sem, this change does not cause major changes.

	- add a flag to mmu_notifier_[un]register routines to indicate
	  if mmap_sem is already locked.


I've temporarily deleted the mm_lock locking of mmap_sem and am continuing to
test. More later....


--- jack
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