Re: [PATCH] fix exit_itimers() vs posix_timer_event() AB-BAdeadlock

[Andrew Morton]

Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
>
> +	/*
>  +	 * We are locking ->it_lock + tasklist_lock backwards
>  +	 * from release_task()->exit_itimers(), beware deadlock.
>  +	 */
>  +	leader = timr->it_process->group_leader;
>  +	while (unlikely(!read_trylock(&tasklist_lock))) {
>  +		if (leader->flags & PF_EXITING) {
>  +			smp_rmb();
>  +			if (thread_group_empty(leader))
>  +				return 0;
>  +		}
>  +		cpu_relax();
>  +	}

Oh dear.  Is there no way to fix this up by taking the locks in the correct
order?  (Whatever that is).

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