On Mon, 2011-01-24 at 15:34 +0100, Oleg Nesterov wrote: > On 01/24, Peter Zijlstra wrote: > > > > On Fri, 2011-01-21 at 16:33 +0100, Peter Zijlstra wrote: > > > > > Index: linux-2.6/mm/rmap.c > > > =================================================================== > > > --- linux-2.6.orig/mm/rmap.c > > > +++ linux-2.6/mm/rmap.c > > > @@ -1559,9 +1559,20 @@ void __put_anon_vma(struct anon_vma *ano > > > * Synchronize against page_lock_anon_vma() such that > > > * we can safely hold the lock without the anon_vma getting > > > * freed. > > > + * > > > + * Relies on the full mb implied by the atomic_dec_and_test() from > > > + * put_anon_vma() against the full mb implied by mutex_trylock() from > > > + * page_lock_anon_vma(). This orders: > > > + * > > > + * page_lock_anon_vma() VS put_anon_vma() > > > + * mutex_trylock() atomic_dec_and_test() > > > + * smp_mb() smp_mb() > > > + * atomic_read() mutex_is_locked() > > > > Bah!, I thought all mutex_trylock() implementations used an atomic op > > with return value (which implies a mb), but it looks like (at least*) > > PPC doesn't and only provides a LOCK barrier. > > But, mutex_trylock() must imply the one-way barrier, otherwise it > is buggy, no? > If this atomic_read() can leak out of the critical section, then > I think mutex_trylock() should be fixed. Or I misunderstood the > problem completely... It implies the LOCK barrier, the one way permeable thing, not a full mb. But I'm not sure the LOCK is sufficient to make the above scenario work. > BTW, from https://lkml.org/lkml/2010/11/26/213 > > + * Similar to page_get_anon_vma() except it locks the anon_vma. > ... > - struct anon_vma *anon_vma = page_get_anon_vma(page); > > looks like, page_get_anon_vma() becomes unused. In my current tree there's two left in mm/migrate.c. git://git.kernel.org/pub/scm/linux/kernel/git/peterz/linux-2.6-mmu_preempt.git HEAD: 7e23542fae47ed3b811583cb925837e3aa7a3f0f -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
