Hi Catalin,

Thanks for your suggestion.

I wonder whether we can shorten this function a bit. Not sure it would
be more readable but it would be shorter.

On Wed, Jan 21, 2026 at 07:06:21PM +0000, Yeoreum Yun wrote:

quoted

+static __always_inline int
+__lsui_cmpxchg32(u32 __user *uaddr, u32 oldval, u32 newval, u32 *oval)
+{
+	u64 __user *uaddr64;
+	bool futex_on_lo;
+	int ret, i;
+	u32 other, orig_other;
+	union {
+		struct futex_on_lo {
+			u32 val;
+			u32 other;
+		} lo_futex;
+
+		struct futex_on_hi {
+			u32 other;
+			u32 val;
+		} hi_futex;
+
+		u64 raw;
+	} oval64, orig64, nval64;

	union {
		u32 futex[2];
		u64 raw;
	}

quoted

+
+	uaddr64 = (u64 __user *) PTR_ALIGN_DOWN(uaddr, sizeof(u64));
+	futex_on_lo = IS_ALIGNED((unsigned long)uaddr, sizeof(u64));

	futex_pos = (unsigned long)uaddr & 4 ? 1 : 0;

Okay. I'll try.

quoted

+
+	if (futex_on_lo) {
+		oval64.lo_futex.val = oldval;
+		ret = get_user(oval64.lo_futex.other, uaddr + 1);
+	} else {
+		oval64.hi_futex.val = oldval;
+		ret = get_user(oval64.hi_futex.other, uaddr - 1);
+	}

and here use

	get_user(oval64.raw, uaddr64);
	futex[futex_pos] = oldval;

But there is another feedback about this
(though I did first similarly with your suggestion -- use oval64.raw):
  https://lore.kernel.org/all/aXDZGhFQDvoSwdc_@willie-the-truck/ (local)

quoted

+
+	if (ret)
+		return -EFAULT;
+
+	ret = -EAGAIN;
+	for (i = 0; i < FUTEX_MAX_LOOPS; i++) {
+		orig64.raw = nval64.raw = oval64.raw;
+
+		if (futex_on_lo)
+			nval64.lo_futex.val = newval;
+		else
+			nval64.hi_futex.val = newval;
+
+		if (__lsui_cmpxchg64(uaddr64, &oval64.raw, nval64.raw))
+			return -EFAULT;
+
+		if (futex_on_lo) {
+			oldval = oval64.lo_futex.val;
+			other = oval64.lo_futex.other;
+			orig_other = orig64.lo_futex.other;
+		} else {
+			oldval = oval64.hi_futex.val;
+			other = oval64.hi_futex.other;
+			orig_other = orig64.hi_futex.other;
+		}

Something similar here to use futex[futex_pos].

We probably also need to check that the user pointer is 32-bit aligned
and return -EFAULT if not.

Thanks. I'll respin it again ;)

--
Sincerely,
Yeoreum Yun