Messages in this thread | | | Date | Fri, 27 Aug 2010 11:55:46 +0200 | From | Andrea Arcangeli <> | Subject | Re: [PATCH] mm: fix hang on anon_vma->root->lock |
| |
On Thu, Aug 26, 2010 at 06:43:31PM -0700, Hugh Dickins wrote: > some light., I think you're mistaking the role that RCU plays here.
That's exactly correct, I thought it prevented reuse of the slab entry, not only of the whole slab... SLAB_DESTROY_BY_RCU is a lot more tricky to use than I though...
However at the light of this, I think page_lock_anon_vma could have returned a freed and reused anon_vma well before the anon-vma changes.
The anon_vma could have been freed after the first page_mapped check succeed but before taking the spinlock. I think, it worked fine because the rmap walks are robust enough just not to fall apart on a reused anon_vma while the lock is hold. It become a visible problem now because we were unlocking the wrong lock leading to a deadlock. But I guess it wasn't too intentional to return a reused anon_vma out of page_lock_anon_vma.
| |