On 10/25/2012 10:39 AM, Peter Zijlstra wrote: > On Thu, 2012-10-25 at 14:19 +0200, Peter Zijlstra wrote: >> On Wed, 2012-10-24 at 17:08 -0700, David Rientjes wrote: >>> Ok, this looks the same but it's actually a different issue: >>> mpol_misplaced(), which now only exists in linux-next and not in 3.7-rc2, >>> calls get_vma_policy() which may take the shared policy mutex. This >>> happens while holding page_table_lock from do_huge_pmd_numa_page() but >>> also from do_numa_page() while holding a spinlock on the ptl, which is >>> coming from the sched/numa branch. >>> >>> Is there anyway that we can avoid changing the shared policy mutex back >>> into a spinlock (it was converted in b22d127a39dd ["mempolicy: fix a race >>> in shared_policy_replace()"])? >>> >>> Adding Peter, Rik, and Mel to the cc. >> >> Urgh, crud I totally missed that. >> >> So the problem is that we need to compute if the current page is placed >> 'right' while holding pte_lock in order to avoid multiple pte_lock >> acquisitions on the 'fast' path. >> >> I'll look into this in a bit, but one thing that comes to mind is having >> both a spnilock and a mutex and require holding both for modification >> while either one is sufficient for read. >> >> That would allow sp_lookup() to use the spinlock, while insert and >> replace can hold both. >> >> Not sure it will work for this, need to stare at this code a little >> more. > > So I think the below should work, we hold the spinlock over both rb-tree > modification as sp free, this makes mpol_shared_policy_lookup() which > returns the policy with an incremented refcount work with just the > spinlock. > > Comments? > > --- It made the warnings I've reported go away. Thanks, Sasha -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>