Re: Robust futexes

[Darren Hart]

Rusty Russell wrote:
> Hi Ingo, all,
>
> 	Noticed (via LWN, hence the delay) your robust futex work.  Have you
> considered the less-perfect, but simpler option of simply having futex
> calls which tell the kernel that the u32 value is in fact the holder's
> TID?
>
> 	In this case, you don't get perfect robustness when TID wrap occurs:
> the kernel won't know that the lock holder is dead.  However, it's
> simple, and telling the kernel that the lock is the tid allows the
> kernel to do prio inheritence etc. in future.

Priority Inheritance has come up a couple of times in relation to Ingo's new 
LightWeight Robust Futexes.  Ingo has said that PI is orthogonal to LWRF, but I 
don't think we've heard if there are plans already in the works (or in his head 
:-) for PI.  Rusty's comment above reads as "the current LWRF implementation 
cannot support PI" - is there something about it that makes PI impractical to 
implement?

Thanks,

--
Darren Hart
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