Messages in this thread | | | Date | Fri, 9 Apr 2010 13:11:40 +1000 | From | Nick Piggin <> | Subject | Re: [PATCH 01/13] powerpc: Add rcu_read_lock() to gup_fast() implementation |
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It's not wrong per se, but the entire powerpc memory management code does the IRQ disabling for its pagetable RCU code. So I think it would be better to do the whole thing in one go.
I don't think Paul will surprise-break powerpc :)
It's up to Ben really, though.
On Thu, Apr 08, 2010 at 09:17:38PM +0200, Peter Zijlstra wrote: > The powerpc page table freeing relies on the fact that IRQs hold off > an RCU grace period, this is currently true for all existing RCU > implementations but is not an assumption Paul wants to support. > > Therefore, also take the RCU read lock along with disabling IRQs to > ensure the RCU grace period does at least cover these lookups. > > Requested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> > Cc: Nick Piggin <npiggin@suse.de> > Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> > --- > arch/powerpc/mm/gup.c | 3 +++ > 1 file changed, 3 insertions(+) > > Index: linux-2.6/arch/powerpc/mm/gup.c > =================================================================== > --- linux-2.6.orig/arch/powerpc/mm/gup.c > +++ linux-2.6/arch/powerpc/mm/gup.c > @@ -142,6 +142,7 @@ int get_user_pages_fast(unsigned long st > * So long as we atomically load page table pointers versus teardown, > * we can follow the address down to the the page and take a ref on it. > */ > + rcu_read_lock(); > local_irq_disable(); > > pgdp = pgd_offset(mm, addr); > @@ -162,6 +163,7 @@ int get_user_pages_fast(unsigned long st > } while (pgdp++, addr = next, addr != end); > > local_irq_enable(); > + rcu_read_unlock(); > > VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT); > return nr; > @@ -171,6 +173,7 @@ int get_user_pages_fast(unsigned long st > > slow: > local_irq_enable(); > + rcu_read_unlock(); > slow_irqon: > pr_devel(" slow path ! nr = %d\n", nr); > >
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