On Sat, Jun 11, 2011 at 06:39:43PM +0200, Andrea Arcangeli wrote: > On Sat, Jun 11, 2011 at 09:04:14AM -0700, Hugh Dickins wrote: > > I had another go at reproducing it, 2 hours that time, then a try with > > 692e0b35427a reverted: it ran overnight for 9 hours when I stopped it. > > > > Andrea, please would you ask Linus to revert that commit before -rc3? > > Or is there something else you'd like us to try instead? I admit that > > I've not actually taken the time to think through exactly how it goes > > wrong, but it does look dangerous. > > Here I was asked if the mem_cgroup_newpage_charge need the mmap_sem at > all. And if not why not to release the mmap_sem early. > > https://lkml.org/lkml/2011/3/14/276 > > So I didn't see why mmap_sem was needed, I also asked confirmation and > who answered agreed it was safe without mmap_sem even if it's the only > place doing that. Maybe that assumption was wrong and we need > mmap_sem after all if this commit is causing problems. > > Or did you find something wrong in the actual patch? > > Do I understand right that the bug just that we must run > alloc_hugepage_vma+mem_cgroup_newpage_charge within the same critical > section protected by the mmap_sem read mode? Do we know why? The problem is that mm->owner points to a stale task structure if the last possible owner is exiting. The mmap_sem just prevented the task from actually exiting through write-acquiring the mmap_sem in khugepaged_exit(). I think enforcing lifetime of an object through locks is not the nicest thing to do, so I stand by what I wrote in the mail you linked to above :) and agree with Kame that mm->owner should just not point to a stale task struct. The memcg code can handle it going NULL. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>