linux-kernel - [tip:sched/core] sched/preempt, futex: Disable preemption in UP futex_atomic_op

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Date:	Tue, 19 May 2015 00:20:26 -0700
From:	tip-bot for David Hildenbrand <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	dahi@...ux.vnet.ibm.com, mingo@...nel.org,
	torvalds@...ux-foundation.org, peterz@...radead.org,
	linux-kernel@...r.kernel.org, hpa@...or.com, tglx@...utronix.de
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@...ux.vnet.ibm.com>
AuthorDate: Mon, 11 May 2015 17:52:13 +0200
Committer:  Ingo Molnar <mingo@...nel.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@...utronix.de>
Signed-off-by: David Hildenbrand <dahi@...ux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: David.Laight@...LAB.COM
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: airlied@...ux.ie
Cc: akpm@...ux-foundation.org
Cc: benh@...nel.crashing.org
Cc: bigeasy@...utronix.de
Cc: borntraeger@...ibm.com
Cc: daniel.vetter@...el.com
Cc: heiko.carstens@...ibm.com
Cc: herbert@...dor.apana.org.au
Cc: hocko@...e.cz
Cc: hughd@...gle.com
Cc: mst@...hat.com
Cc: paulus@...ba.org
Cc: ralf@...ux-mips.org
Cc: schwidefsky@...ibm.com
Cc: yang.shi@...driver.com
Link: http://lkml.kernel.org/r/1431359540-32227-9-git-send-email-dahi@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@...nel.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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