On Wed, Aug 25, 2010 at 11:41 PM, David Miller <davem@xxxxxxxxxxxxx> wrote: > From: Hugh Dickins <hughd@xxxxxxxxxx> > 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@xxxxxxxxxx> > > 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 -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>