Re: [PATCH v2 0/4] futex: Drop ROBUST_LIST_LIMIT

[André Almeida]

Hi Florian,

Em 28/01/2025 04:50, Florian Weimer escreveu:
> * André Almeida:
>
> > As requested by Peter at [1], this patchset drops the
> > ROBUST_LIST_LIMIT. This is achieve by simply rewriting the processed
> > list element ->next to point to the head->list address, destroying the
> > linked list to avoid any circular list.
>
> Doesn't this turn a robust mutex overwrite or a TCB overwrite into a
> write-anything-anywhere primitive?  Furthermore, I'm not entirely sure
> if this is entirely backwards-compatible.

The robust list is meant to be a private resource, per-process, and this 
patch only rewrites it after the process exits, so I believe that any 
changes done in this memory should be safe given that the process will 
soon disappear anyway, right?

Do you think you can point out a scenario that wouldn't be 
backwards-compatible? I would like to try to test it.

> Could you use the tortoise/hare approach instead?

I believe that you want the approach to be "slow and steady" but I'm not 
sure what you have in mind, if you could you please elaborate :)

> Thanks,
> Florian