Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1201734

[PATCH 5/4] ARC: ensure futex ops are atomic in !LLSC config

Show all headers | View raw

W/o hardware assisted atomic r-m-w the best we can do is to disable
preemption.

Cc: David Hildenbrand <dahi@linux.vnet.ibm.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Michel Lespinasse <walken@google.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
---
 arch/arc/include/asm/futex.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/arc/include/asm/futex.h b/arch/arc/include/asm/futex.h
index 0ea8bcc7b846..8f449982523b 100644
--- a/arch/arc/include/asm/futex.h
+++ b/arch/arc/include/asm/futex.h
@@ -87,6 +87,9 @@ static inline int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
 	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
 		return -EFAULT;
 
+#ifndef CONFIG_ARC_HAS_LLSC
+	preempt_disable();	/* to guarantee atomic r-m-w of futex op */
+#endif
 	pagefault_disable();
 
 	switch (op) {
@@ -111,6 +114,9 @@ static inline int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
 	}
 
 	pagefault_enable();
+#ifndef CONFIG_ARC_HAS_LLSC
+	preempt_enable();
+#endif
 
 	if (!ret) {
 		switch (cmp) {
@@ -153,6 +159,9 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr, u32 expval,
 	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
 		return -EFAULT;
 
+#ifndef CONFIG_ARC_HAS_LLSC
+	preempt_disable();	/* to guarantee atomic r-m-w of futex op */
+#endif
 	smp_mb();
 
 	__asm__ __volatile__(
@@ -182,6 +191,9 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr, u32 expval,
 
 	smp_mb();
 
+#ifndef CONFIG_ARC_HAS_LLSC
+	preempt_enable();
+#endif
 	*uval = existval;
 	return ret;
 }
-- 
1.9.1

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH 0/4] ARC futex fixes Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-08-06 14:50 +0200
  [PATCH 5/4] ARC: ensure futex ops are atomic in !LLSC config Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-08-06 15:50 +0200
  Re: [PATCH 0/4] ARC futex fixes Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-08-17 09:50 +0200

csiph-web