[lkml]   [2010]   [Aug]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [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.

 \ /
  Last update: 2010-08-27 11:59    [W:0.049 / U:43.052 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site