[PATCH 01/13] powerpc: Add rcu_read_lock() to gup_fast() implementation

Peter Zijlstra
2010-04-08T19:17:38Z

[-- Attachment #1: powerpc-gup_fast-rcu.patch --]
[-- Type: text/plain, Size: 1467 bytes --]

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);