Hi Greentime,

On Wed, Nov 08, 2017 at 01:54:59PM +0800, Greentime Hu wrote:

From: Greentime Hu <redacted>

Signed-off-by: Vincent Chen <redacted>
Signed-off-by: Greentime Hu <redacted>
---
 arch/nds32/include/asm/futex.h    |  116 ++++++++++++++++++++++++
 arch/nds32/include/asm/spinlock.h |  178 +++++++++++++++++++++++++++++++++++++
 2 files changed, 294 insertions(+)
 create mode 100644 arch/nds32/include/asm/futex.h
 create mode 100644 arch/nds32/include/asm/spinlock.h

[...]

+static inline int
+futex_atomic_cmpxchg_inatomic(u32 * uval, u32 __user * uaddr,
+			      u32 oldval, u32 newval)
+{
+	int ret = 0;
+	u32 val, tmp, flags;
+
+	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
+		return -EFAULT;
+
+	smp_mb();
+	asm volatile ("       movi    $ta, #0\n"
+		      "1:     llw     %1, [%6 + $ta]\n"
+		      "       sub     %3, %1, %4\n"
+		      "       cmovz   %2, %5, %3\n"
+		      "       cmovn   %2, %1, %3\n"
+		      "2:     scw     %2, [%6 + $ta]\n"
+		      "       beqz    %2, 1b\n"
+		      "3:\n                   " __futex_atomic_ex_table("%7")
+		      :"+&r"(ret), "=&r"(val), "=&r"(tmp), "=&r"(flags)
+		      :"r"(oldval), "r"(newval), "r"(uaddr), "i"(-EFAULT)
+		      :"$ta", "memory");
+	smp_mb();
+
+	*uval = val;
+	return ret;
+}

I see you rely on asm-generic/barrier.h for your barrier definitions, which
suggests that you only need to prevent reordering by the compiler because
you're not SMP. Is that right? If so, using smp_mb() is a little weird.

What about DMA transactions? I imagine you might need some extra
instructions for the mandatory barriers there.

Also:

+static inline void arch_spin_lock(arch_spinlock_t * lock)
+{
+	unsigned long tmp;
+
+	__asm__ __volatile__("1:\n"
+			     "\tllw\t%0, [%1]\n"
+			     "\tbnez\t%0, 1b\n"
+			     "\tmovi\t%0, #0x1\n"
+			     "\tscw\t%0, [%1]\n"
+			     "\tbeqz\t%0, 1b\n"
+			     :"=&r"(tmp)
+			     :"r"(&lock->lock)
+			     :"memory");
+}

Here it looks like you're eliding an explicit barrier here because you
already have a "memory" clobber. Can't you do the same for the futex code
above?

Will