futex: Use user_write_access_begin/_end() in futex_put_value()

Commit cec199c ("futex: Implement FUTEX2_NUMA") introduced the
futex_put_value() helper to write a value to the given user
address.

However, it uses user_read_access_begin() before the write. For
architectures that differentiate between read and write accesses, like
PowerPC, futex_put_value() fails with -EFAULT.

Fix that by using the user_write_access_begin/user_write_access_end() pair
instead.

Fixes: cec199c ("futex: Implement FUTEX2_NUMA")
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Cc: [email protected]
Link: https://lore.kernel.org/all/[email protected]

Author: Waiman-Long

kernel/futex/futex.h

@@ -319,13 +319,13 @@ static __always_inline int futex_put_value(u32 val, u32 __user *to)
 {
 	if (can_do_masked_user_access())
 		to = masked_user_access_begin(to);
-	else if (!user_read_access_begin(to, sizeof(*to)))
+	else if (!user_write_access_begin(to, sizeof(*to)))
 		return -EFAULT;
 	unsafe_put_user(val, to, Efault);
-	user_read_access_end();
+	user_write_access_end();
 	return 0;
 Efault:
-	user_read_access_end();
+	user_write_access_end();
 	return -EFAULT;
 }