Commit-ID: 388b0e0adbc98a1b12a077dc92851a3ce016db42
Gitweb: http://git.kernel.org/tip/388b0e0adbc98a1b12a077dc92851a3ce016db42
Author: David Hildenbrand <d...@linux.vnet.ibm.com>
AuthorDate: Mon, 11 May 2015 17:52:16 +0200
Committer: Ingo Molnar <mi...@kernel.org>
CommitDate: Tue, 19 May 2015 08:39:17 +0200
sched/preempt, arm/futex: Disable preemption in UP futex_atomic_op_inuser()
explicitly
The !CONFIG_SMP implementation of futex_atomic_op_inuser() seems to rely
on disabled preemption to guarantee mutual exclusion.
>From commit e589ed23dd27 ("[ARM] 5218/1: arm: improved futex support"):
"For UP it's enough to disable preemption to ensure mutual exclusion..."
>From the code itself:
"!SMP, we can work around lack of atomic ops by disabling preemption"
Let's make this explicit, to prepare for pagefault_disable() not
touching preemption anymore.
Reviewed-and-tested-by: Thomas Gleixner <t...@linutronix.de>
Signed-off-by: David Hildenbrand <d...@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Cc: david.lai...@aculab.com
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: airl...@linux.ie
Cc: a...@linux-foundation.org
Cc: b...@kernel.crashing.org
Cc: bige...@linutronix.de
Cc: borntrae...@de.ibm.com
Cc: daniel.vet...@intel.com
Cc: heiko.carst...@de.ibm.com
Cc: herb...@gondor.apana.org.au
Cc: ho...@suse.cz
Cc: hu...@google.com
Cc: m...@redhat.com
Cc: pau...@samba.org
Cc: r...@linux-mips.org
Cc: schwidef...@de.ibm.com
Cc: yang....@windriver.com
Link:
http://lkml.kernel.org/r/1431359540-32227-12-git-send-email-d...@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mi...@kernel.org>
---
arch/arm/include/asm/futex.h | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/arch/arm/include/asm/futex.h b/arch/arm/include/asm/futex.h
index 255bfd1..5eed828 100644
--- a/arch/arm/include/asm/futex.h
+++ b/arch/arm/include/asm/futex.h
@@ -127,7 +127,10 @@ futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
return -EFAULT;
- pagefault_disable(); /* implies preempt_disable() */
+#ifndef CONFIG_SMP
+ preempt_disable();
+#endif
+ pagefault_disable();
switch (op) {
case FUTEX_OP_SET:
@@ -149,7 +152,10 @@ futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
ret = -ENOSYS;
}
- pagefault_enable(); /* subsumes preempt_enable() */
+ pagefault_enable();
+#ifndef CONFIG_SMP
+ preempt_enable();
+#endif
if (!ret) {
switch (cmp) {
--
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