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

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Date:	Tue, 19 May 2015 00:20:45 -0700
From:	tip-bot for David Hildenbrand <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	peterz@...radead.org, mingo@...nel.org, hpa@...or.com,
	dahi@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, torvalds@...ux-foundation.org
Subject: [tip:sched/core] sched/preempt, futex:
  Disable preemption in UP futex_atomic_cmpxchg_inatomic() explicitly

Commit-ID:  d9b9ff8c18891d74dc7076800bde81b774f7d032
Gitweb:     http://git.kernel.org/tip/d9b9ff8c18891d74dc7076800bde81b774f7d032
Author:     David Hildenbrand <dahi@...ux.vnet.ibm.com>
AuthorDate: Mon, 11 May 2015 17:52:14 +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_cmpxchg_inatomic() explicitly

Let's explicitly disable/enable preemption in the !CONFIG_SMP version
of futex_atomic_cmpxchg_inatomic(), to prepare for pagefault_disable() not
touching preemption anymore. This is needed for this function to be
callable from both, atomic and non-atomic context.

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/1431359540-32227-10-git-send-email-dahi@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 include/asm-generic/futex.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/asm-generic/futex.h b/include/asm-generic/futex.h
index 3586017..e56272c 100644
--- a/include/asm-generic/futex.h
+++ b/include/asm-generic/futex.h
@@ -107,6 +107,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 {
 	u32 val;
 
+	preempt_disable();
 	if (unlikely(get_user(val, uaddr) != 0))
 		return -EFAULT;
 
@@ -114,6 +115,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 		return -EFAULT;
 
 	*uval = val;
+	preempt_enable();
 
 	return 0;
 }
--
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