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Message-Id: <1430934639-2131-12-git-send-email-dahi@linux.vnet.ibm.com>
Date: Wed, 6 May 2015 19:50:35 +0200
From: David Hildenbrand <dahi@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: dahi@...ux.vnet.ibm.com, mingo@...hat.com, peterz@...radead.org,
yang.shi@...driver.com, bigeasy@...utronix.de,
benh@...nel.crashing.org, paulus@...ba.org,
akpm@...ux-foundation.org, heiko.carstens@...ibm.com,
schwidefsky@...ibm.com, borntraeger@...ibm.com, mst@...hat.com,
tglx@...utronix.de, David.Laight@...LAB.COM, hughd@...gle.com,
hocko@...e.cz, ralf@...ux-mips.org, herbert@...dor.apana.org.au,
linux@....linux.org.uk, airlied@...ux.ie, daniel.vetter@...el.com,
linux-mm@...ck.org, linux-arch@...r.kernel.org
Subject: [PATCH RFC 11/15] arm/futex: UP futex_atomic_op_inuser() relies on disabled preemption
The !CONFIG_SMP implementation of futex_atomic_op_inuser() seems to rely
on disabled preemption to guarantee mutual exclusion.
>From commit e589ed23dd27:
"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.
Signed-off-by: David Hildenbrand <dahi@...ux.vnet.ibm.com>
---
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) {
--
2.1.4
--
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