Re: [PATCH] Don't apply for write lock on tasklist_lock if parent doesn't ptrace other processes

[Roland McGrath <roland@redhat.com>]

> So, this list_empty() check needs taskslit at least for reading. But, we
> are going to take it for writing right after exit_ptrace() returns, afaics
> we can add this fastpatch check for free.

That looks good to me, but it could use some more scare comments.

>  /*
> - * Detach all tasks we were using ptrace on.
> + * Detach all tasks we were using ptrace on. Called with tasklist held.

 * Called with tasklist held for writing, and returns with it held too.
 * But note it can release and reacquire the lock.

> +	write_lock_irq(&tasklist_lock);
> +
	/*
	 * Note that exit_ptrace() might drop tasklist_lock and reacquire it.
	 */
>  	exit_ptrace(father);
>  
> -	write_lock_irq(&tasklist_lock);
>  	reaper = find_new_reaper(father);


Thanks,
Roland