[PATCH v1 08/15] futex: UP futex_atomic_op_inuser() relies on disabled preemption

David Hildenbrand
2015-05-11T15:53:04Z

Let's explicitly disable/enable preemption in the !CONFIG_SMP version
of futex_atomic_op_inuser, to prepare for pagefault_disable() not
touching preemption anymore.

Otherwise we might break mutual exclusion when relying on a get_user()/
put_user() implementation.

Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
---
include/asm-generic/futex.h | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/asm-generic/futex.h b/include/asm-generic/futex.h
index b59b5a5..3586017 100644
--- a/include/asm-generic/futex.h
+++ b/include/asm-generic/futex.h
@@ -8,8 +8,7 @@
#ifndef CONFIG_SMP
/*
* The following implementation only for uniprocessor machines.
- * For UP, it's relies on the fact that pagefault_disable() also disables
- * preemption to ensure mutual exclusion.
+ * It relies on preempt_disable() ensuring mutual exclusion.
*
*/

@@ -38,6 +37,7 @@ futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
oparg = 1 << oparg;

+ preempt_disable();
pagefault_disable();

ret = -EFAULT;
@@ -72,6 +72,7 @@ futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)

out_pagefault_enable:
pagefault_enable();
+ preempt_enable();

if (ret == 0) {
switch (cmp) {
--
2.1.4