linux-kernel - Re: [PATCH] kthread: Enhance kthread_stop to abort interruptible sleeps

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20070414183538.GB504@tv-sign.ru>
Date:	Sat, 14 Apr 2007 22:35:38 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Davide Libenzi <davidel@...ilserver.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Roland McGrath <roland@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH] kthread: Enhance kthread_stop to abort interruptible sleeps

On 04/13, Eric W. Biederman wrote:
>
> +static inline int __kthread_should_stop(struct task_struct *tsk)
> +{
> +	return test_tsk_thread_flag(tsk, TIF_KTHREAD_STOP);
> +}

Am I blind? Where does copy_process/dup_task_struct clears unwanted
flags in thread_info->flags ?

> +int kthread_stop(struct task_struct *tsk)
>  {
>  	int ret;
>  
> -	mutex_lock(&kthread_stop_lock);
> -
> -	/* It could exit after stop_info.k set, but before wake_up_process. */
> -	get_task_struct(k);
> +	/* Ensure the task struct persists until I read the exit code. */
> +	get_task_struct(tsk);
>  
> -	/* Must init completion *before* thread sees kthread_stop_info.k */
> -	init_completion(&kthread_stop_info.done);
> -	smp_wmb();
> +	set_tsk_thread_flag(tsk, TIF_KTHREAD_STOP);
> +	spin_lock_irq(&tsk->sighand->siglock);
> +	signal_wake_up(tsk, 1);
> +	spin_unlock_irq(&tsk->sighand->siglock);

Off-topic again, the comment above signal_wake_up() is very confusing...
I think the only reason for ->siglock is to prevent the case when
TIF_SIGPENDING may be cleared by recalc_sigpending(). Or something else?

This changes the current API, kthread_stop() doesn't wake up UNINTERRUPTIBLE
tasks any longer. I'd say this is good, but may break things ... For example,
kthred_stop(kthread_create(...)) can't work now.

> -	/* Now set kthread_should_stop() to true, and wake it up. */
> -	kthread_stop_info.k = k;
> -	wake_up_process(k);
> -	put_task_struct(k);
> +	wait_for_completion(tsk->vfork_done);
> +	ret = tsk->exit_code;

This is really good. Now the kernel thread can exit() at any point without
fear to break kthread_stop().

> @@ -218,7 +219,7 @@ static inline int has_pending_signals(sigset_t *signal, sigset_t *blocked)
>  fastcall void recalc_sigpending_tsk(struct task_struct *t)
>  {
>  	if (t->signal->group_stop_count > 0 ||
> -	    (freezing(t)) ||
> +	    (freezing(t)) || __kthread_should_stop(t) ||
>  	    PENDING(&t->pending, &t->blocked) ||
>  	    PENDING(&t->signal->shared_pending, &t->blocked))
>  		set_tsk_thread_flag(t, TIF_SIGPENDING);

Aha, now I understand your point about interruptible sleeps (the previous
message). What is the reason for this change?

Oleg.

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/