On Mon, Jul 31 2023 at 21:20, Peter Zijlstra wrote:
> -#define FUTEX2_MASK (FUTEX2_64 | FUTEX2_PRIVATE)
> +#define FUTEX2_MASK (FUTEX2_SIZE_MASK | FUTEX2_PRIVATE)
Along with some comment which documents that the size "flags" constitute
a number field and not flags in the sense of binary flags.
And please name these size constants so it really becomes obvious:
#define FUTEX2_SIZE_U32 2
> /**
> * futex_parse_waitv - Parse a waitv array from userspace
> @@ -208,11 +208,11 @@ static int futex_parse_waitv(struct fute
> return -EINVAL;
>
> if (!IS_ENABLED(CONFIG_64BIT) || in_compat_syscall()) {
> - if ((aux.flags & FUTEX2_64) == FUTEX2_64)
> + if ((aux.flags & FUTEX2_SIZE_MASK) == FUTEX2_64)
> return -EINVAL;
> }
That should be part of the actual 64bit futex enablement, no?
> - if ((aux.flags & FUTEX2_64) != FUTEX2_32)
> + if ((aux.flags & FUTEX2_SIZE_MASK) != FUTEX2_32)
> return -EINVAL;
In hindsight I think it was as mistake just to have this __u32 flags
field in the new interface. Soemthing like the incomplete below might be
retrofittable, no?
--- a/include/uapi/linux/futex.h
+++ b/include/uapi/linux/futex.h
@@ -74,7 +74,12 @@
struct futex_waitv {
__u64 val;
__u64 uaddr;
- __u32 flags;
+ union {
+ __u32 flags;
+ __u32 size : 2,
+ : 5,
+ private : 1;
+ };
__u32 __reserved;
};
--- a/kernel/futex/syscalls.c
+++ b/kernel/futex/syscalls.c
@@ -204,10 +204,10 @@ static int futex_parse_waitv(struct fute
if (copy_from_user(&aux, &uwaitv[i], sizeof(aux)))
return -EFAULT;
- if ((aux.flags & ~FUTEX2_MASK) || aux.__reserved)
+ if ((aux.flags & ~FUTEX2_VALID_FLAGBITS) || aux.__reserved)
return -EINVAL;
- if (!(aux.flags & FUTEX2_32))
+ if (aux.size != FUTEX2_SIZE_U32)
return -EINVAL;
futexv[i].w.flags = aux.flags;
If this muck already confused me right now, then I don't want to
experience the confusion factor 6 month down the road :)
Thanks,
tglx
