lkml.org 
[lkml]   [2010]   [Apr]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 01/13] powerpc: Add rcu_read_lock() to gup_fast() implementation
    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);
    >
    >


    \
     
     \ /
      Last update: 2010-04-09 05:15    [W:0.047 / U:31.992 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site