| Submitter | Andrew Morton |
|---|---|
| Date | April 27, 2010, 9:10 p.m. |
| Message ID | <201004272110.o3RLAl7P019943@imap1.linux-foundation.org> |
| Download | mbox | patch |
| Permalink | /patch/51102/ |
| State | Rejected |
| Headers | show |
Comments
On Tue, Apr 27, 2010 at 02:10:47PM -0700, Andrew Morton wrote: > From: Peter Zijlstra <a.p.zijlstra@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.zijlstra@chello.nl> > Requested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > Cc: Nick Piggin <npiggin@suse.de> > Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> > Reviewed-by: Rik van Riel <riel@redhat.com> > Signed-off-by: Andrew Morton <akpm@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); > > _
On Wed, 2010-04-28 at 13:29 +1000, Nick Piggin wrote: > 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. Right, on my todo list. Cheers, Ben.
On Tue, 2010-04-27 at 14:10 -0700, akpm@linux-foundation.org wrote: > From: Peter Zijlstra <a.p.zijlstra@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. Nah, that's not right. The right fix is to use call_rcu_sched() from the powerpc page table freeing code. Please drop. Cheers, Ben. > Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> > Requested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > Cc: Nick Piggin <npiggin@suse.de> > Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> > Reviewed-by: Rik van Riel <riel@redhat.com> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org> > --- > > 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); > > _
Patch
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);