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Subject[tip:sched/core] sched/preempt, futex: Disable preemption in UP futex_atomic_op_inuser() explicitly
Commit-ID:  f3dae07e442a8131a5485b6a38db2aa22a7a48cf
Gitweb: http://git.kernel.org/tip/f3dae07e442a8131a5485b6a38db2aa22a7a48cf
Author: David Hildenbrand <dahi@linux.vnet.ibm.com>
AuthorDate: Mon, 11 May 2015 17:52:13 +0200
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 19 May 2015 08:39:16 +0200

sched/preempt, futex: Disable preemption in UP futex_atomic_op_inuser() explicitly

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.

Reviewed-and-tested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: David.Laight@ACULAB.COM
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: airlied@linux.ie
Cc: akpm@linux-foundation.org
Cc: benh@kernel.crashing.org
Cc: bigeasy@linutronix.de
Cc: borntraeger@de.ibm.com
Cc: daniel.vetter@intel.com
Cc: heiko.carstens@de.ibm.com
Cc: herbert@gondor.apana.org.au
Cc: hocko@suse.cz
Cc: hughd@google.com
Cc: mst@redhat.com
Cc: paulus@samba.org
Cc: ralf@linux-mips.org
Cc: schwidefsky@de.ibm.com
Cc: yang.shi@windriver.com
Link: http://lkml.kernel.org/r/1431359540-32227-9-git-send-email-dahi@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
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) {

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