lkml.org 
[lkml]   [2010]   [Apr]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH 01/13] powerpc: Add rcu_read_lock() to gup_fast() implementation
    From
    Date
    On Thu, 2010-04-08 at 21:17 +0200, Peter Zijlstra wrote:
    > plain text document attachment (powerpc-gup_fast-rcu.patch)
    > 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.

    There's a few other places that need a similar fix then. The hash page
    code for example. All the C cases should end up calling the
    find_linux_pte() helper afaik, so we should be able to stick the lock in
    there (and the hugetlbfs variant, find_linux_pte_or_hugepte()).

    However, we also have cases of tight asm code walking the page tables,
    such as the tlb miss handler on embedded processors. I don't see how I
    could do that there. IE. I only have a handful of registers to play
    with, no stack, etc...

    So we might have to support the interrupt assumption, at least in some
    form, with those guys...

    Cheers,
    Ben.

    > 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: 2010-04-13 03:11    [W:0.031 / U:0.444 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site