Re: [PATCH] fix wait_task_inactive race (was Re: Race condition inptrace)

[Nick Piggin]

Nick Piggin wrote:
> Ingo Molnar wrote:
>
> > * Nick Piggin <nickpiggin@xxxxxxxxxxxx> wrote:
> >
> >
> > > When a task is put to sleep, it is dequeued from the runqueue
> > > while it is still running. The problem is that the runqueue
> > > lock can be dropped and retaken in schedule() before the task
> > > actually schedules off, and wait_task_inactive did not account
> > > for this.
> >
> >
> >
> > ugh. This has been the Nth time we got bitten by the fundamental
> > unrobustness of non-atomic scheduling on some architectures ...
> > (And i'll say the N+1th time that this is not good.)
>
> This is actually due to wake_sleeping_dependent and
> dependent_sleeper dropping the runqueue lock.

Hmph, *and* unlocked context switch architectures as you say.
In fact, I'm surprised those haven't been bitten by this problem
earlier.

So that makes us each half right! :)

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