Re: [PATCH RFC] sched: Revert delayed_put_task_struct() and fix use after free

[Oleg Nesterov]

On 10/16, Kirill Tkhai wrote:
>
> Cool! Elegant fix. We set PF_EXITING in exit_signals(), which is earlier
> than release_task() is called.

OK, thanks, I am sending the patch...

> Shouldn't we use smp_rmb/smp_wmb here?

No, we do not. call_rcu(delayed_put_pid) itself implies the barrier on
all CPUs. IOW, by the time RCU actually calls delayed_put_pid() every
CPU must see all memory changes which were done before call_rcu() was
called. And otoh, all rcu-read-lock critical sections which could miss
PF_EXITING should be already finished.

Oleg.

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