On Tue, Mar 16 2021 at 11:03, Davidlohr Bueso wrote: > On Tue, 16 Mar 2021, Peter Zijlstra wrote: >>IIRC we made the explicit choice to never loop here. That saves having >>to worry about getting stuck in in-kernel loops. >> >>Userspace triggering the case where the futex goes corrupt is UB, after >>that we have no obligation for anything to still work. It's on them, >>they get to deal with the bits remaining. > > I was kind of expecting this answer, honestly. After all, we are warned > about violations to the 10th: > > * [10] There is no transient state which leaves owner and user space > * TID out of sync. Except one error case where the kernel is denied > * write access to the user address, see fixup_pi_state_owner(). > > (btw, should we actually WARN_ON_ONCE this case such that the user is > well aware things are screwed up?) > > However, as 34b1a1ce145 describes, it was cared enough about users to > protect them against spurious runaway tasks. And this is why I decided > to even send the patch; it fixes, without sacrificing performance or > additional complexity, a potentially user visible issue which could be > due to programming error. And unlike 34b1a1ce145, where a stealer that > cannot fault ends up dropping the lock, here the stealer can actually > amend things and not break semantics because of another task's stupidity. > But yeah, this could also be considered in the category of inept attempts > to fix a rotten situation.
It's one of the 'Doctor it hurts when I shoot myself in the foot' cases :)
