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SubjectRe: doublefault debugging (was Re: Linux v2.5.62 --- spontaneous reboots)

On Thu, 20 Feb 2003, Linus Torvalds wrote:

> > a true heisenbug. I cannot reproduce it anymore. Anyway, from the serial
> > console i collected 3 instances of crashes - whatever it's worth.
>
> Pretty much every single time, release_task() has been there on the
> backtrace.
>
> In fact, I bet you this code in do_exit() is the cause:
>
> preempt_disable();
>
> if (tsk->exit_signal == -1)
> *** release_task(tsk); ***
>
> schedule();
>
> Note how "release_task()" will be releasing the stack that the process
> is running on right now. [...]

but, release_task() is a delayed thing for exactly this reason. It fills
out the per-CPU task_cache but does not free the task.

the release_task() + schedule() must be atomic though - ie. we must not be
preempted anytime inbetween [because that other task could free the
task_cache] - but i wasnt running with CONFIG_PREEMPT, so i cannot see how
it could happen.

Ingo

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