Messages in this thread |  | | | Date | Thu, 26 Aug 2010 03:54:28 -0700 | | Subject | Re: [PATCH] mm: fix hang on anon_vma->root->lock | | From | Hugh Dickins <> |
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On Wed, Aug 25, 2010 at 11:41 PM, David Miller <davem@davemloft.net> wrote: > From: Hugh Dickins <hughd@google.com> > Date: Wed, 25 Aug 2010 23:12:54 -0700 (PDT) > >> After several hours, kbuild tests hang with anon_vma_prepare() spinning on >> a newly allocated anon_vma's lock - on a box with CONFIG_TREE_PREEMPT_RCU=y >> (which makes this very much more likely, but it could happen without). >> >> The ever-subtle page_lock_anon_vma() now needs a further twist: since >> anon_vma_prepare() and anon_vma_fork() are liable to change the ->root >> of a reused anon_vma structure at any moment, page_lock_anon_vma() >> needs to check page_mapped() again before succeeding, otherwise >> page_unlock_anon_vma() might address a different root->lock. >> >> Signed-off-by: Hugh Dickins <hughd@google.com> > > Interesting, is the condition which allows this to trigger specific > to this merge window or was it always possible?
Just specific to this merge window, which started using anon_vma->root->lock in place of anon_vma->lock (anon_vma->root is often anon_vma itself, but not always). I _think_ that change was itself a simplification of the locking in 2.6.35, rather than plugging a particular hole (it's not been backported to -stable), but I may be wrong on that - Rik?
Hugh
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