On Fri, Apr 23, 2010 at 11:35:49PM +0200, Andrea Arcangeli wrote: > On Fri, Apr 23, 2010 at 09:39:48PM +0200, Andrea Arcangeli wrote: > > On Fri, Apr 23, 2010 at 08:23:12PM +0100, Mel Gorman wrote: > > > On Fri, Apr 23, 2010 at 08:31:35PM +0200, Andrea Arcangeli wrote: > > > > Hi Mel, > > > > > > > > On Thu, Apr 22, 2010 at 04:44:43PM +0100, Mel Gorman wrote: > > > > > heh, I thought of a similar approach at the same time as you but missed > > > > > this mail until later. However, with this approach I suspect there is a > > > > > possibility that two walkers of the same anon_vma list could livelock if > > > > > two locks on the list are held at the same time. Am still thinking of > > > > > how it could be resolved without introducing new locking. > > > > > > > > Trying to understand this issue and I've some questions. This > > > > vma_adjust and lock inversion troubles with the anon-vma lock in > > > > rmap_walk are a new issue introduced by the recent anon-vma changes, > > > > right? > > > > > > > > > > In a manner of speaking. There was no locking going on but prior to the > > > anon_vma changes, there would have been only one anon_vma lock and the > > > fix would be easier - just take the lock on anon_vma->lock while the > > > VMAs are being updated. > > > > So it was very much a bug before too and we could miss to find some > > pte mapping the page if vm_start was adjusted? > > Well I looked deeper into it myself as I wanted to have this bit (and > other bits) sorted out in aa.git, and definitely this is a bug > introduced by the newest anon-vma changes in 2.6.34-rc so aa.git > cannot be affected as it's using the 2.6.33 anon-vma (and prev) code. > I think you're right. This is a new bug introduced by the anon_vma changes. On the plus side, it means we don't have to worry about -stable. > vma_adjust already takes the anon_vma->lock and of course I also > further verified that trying to apply your snippet to vma_adjust > results in immediately deadlock as the very same lock is already taken > in my tree as it's the same anon-vma (simpler). Yes, I expected that. Previously, there was only one anon_vma so if you double-take the lock, bad things happen. > So aa.git will be > immune from these bugs for now. > It should be. I expect that's why you have never seen the bugon in swapops. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>