ARC: ensure futex ops are atomic in !LLSC config
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>
diff --git a/arch/arc/include/asm/futex.h b/arch/arc/include/asm/futex.h
index 0ea8bcc..8f44998 100644
--- a/arch/arc/include/asm/futex.h
+++ b/arch/arc/include/asm/futex.h
@@ -87,6 +87,9 @@
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 @@
}
pagefault_enable();
+#ifndef CONFIG_ARC_HAS_LLSC
+ preempt_enable();
+#endif
if (!ret) {
switch (cmp) {
@@ -153,6 +159,9 @@
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 @@
smp_mb();
+#ifndef CONFIG_ARC_HAS_LLSC
+ preempt_enable();
+#endif
*uval = existval;
return ret;
}