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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@linux.vnet.ibm.com>
AuthorDate: Mon, 11 May 2015 17:52:14 +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_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@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/1431359540-32227-10-git-send-email-dahi@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.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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