Re: [PATCH v1 02/14] futex: Extend the FUTEX2 flags

On Mon, Jul 31 2023 at 19:35, Peter Zijlstra wrote:

On Mon, Jul 31, 2023 at 07:16:29PM +0200, Thomas Gleixner wrote:

quoted

On Mon, Jul 31 2023 at 18:11, Thomas Gleixner wrote:

quoted

On Fri, Jul 21 2023 at 12:22, Peter Zijlstra wrote:

quoted

-#define FUTEX2_MASK (FUTEX2_32 | FUTEX2_PRIVATE)
+#define FUTEX2_MASK (FUTEX2_64 | FUTEX2_PRIVATE)
 
 /**
  * futex_parse_waitv - Parse a waitv array from userspace

@@ -207,7 +207,12 @@ static int futex_parse_waitv(struct fute
 		if ((aux.flags & ~FUTEX2_MASK) || aux.__reserved)
 			return -EINVAL;

With the above aux.flags with FUTEX2_32 set will result in -EINVAL. I
don't think that's intentional.

Also if you allow 64bit wide futexes, how is that supposed to work with
the existing code, which clearly expects a 32bit uval throughout the
place?

Not allowed yet, these patches only allow 8,16,32. I still need to audit
the whole futex core and do 'u32 -> unsigned long' (and everything else
that follows from that), and only when that's done can the futex2
syscalls allow FUTEX2_64 on 64bit archs.

So for now, these patches:

  - add the FUTEX2_64 flag,
  - add 'unsigned long' interface such that
    64bit can potentiall use it,
  - explicitly disallow having it set.

I figured that out very late. This flags having a size fields which
claims to be flags had confused the hell out of me.