On Tue, Apr 27, 2010 at 02:10:47PM -0700, Andrew Morton wrote:
> From: Peter Zijlstra <a.p.zijls...@chello.nl>
>
> 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.
>
> Signed-off-by: Peter Zijlstra <a.p.zijls...@chello.nl>
> Requested-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> Cc: Nick Piggin <npig...@suse.de>
> Cc: Benjamin Herrenschmidt <b...@kernel.crashing.org>
> Reviewed-by: Rik van Riel <r...@redhat.com>
> Signed-off-by: Andrew Morton <a...@linux-foundation.org>
I think I nacked this because the rest of the powerpc code also
assumes irq disables provide an rcu critical section. The plan was
to convert powerpc pagetable code to use call_rcu_sched.
> ---
>
> arch/powerpc/mm/gup.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff -puN
> arch/powerpc/mm/gup.c~powerpc-add-rcu_read_lock-to-gup_fast-implementation
> arch/powerpc/mm/gup.c
> ---
> a/arch/powerpc/mm/gup.c~powerpc-add-rcu_read_lock-to-gup_fast-implementation
> +++ a/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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