linux-kernel - Re: [PATCH v11 8/8] vhost: use vhost

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Date:   Tue, 16 May 2023 15:18:11 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Mike Christie <michael.christie@...cle.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Christian Brauner <brauner@...nel.org>,
        Thorsten Leemhuis <linux@...mhuis.info>,
        nicolas.dichtel@...nd.com,
        Linux kernel regressions list <regressions@...ts.linux.dev>,
        hch@...radead.org, stefanha@...hat.com, jasowang@...hat.com,
        mst@...hat.com, sgarzare@...hat.com,
        virtualization@...ts.linux-foundation.org, ebiederm@...ssion.com,
        konrad.wilk@...cle.com, linux-kernel@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH v11 8/8] vhost: use vhost_tasks for worker threads

On 05/15, Mike Christie wrote:
>
> Oleg and Christian,
>
>
> Below is an updated patch that doesn't check for PF_USER_WORKER in the
> signal.c code and instead will check for if we have blocked the signal.

Looks like I need to read the whole series... will try tomorrow.

> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -2336,8 +2336,15 @@ __latent_entropy struct task_struct *copy_process(
>  	p->flags &= ~PF_KTHREAD;
>  	if (args->kthread)
>  		p->flags |= PF_KTHREAD;
> -	if (args->user_worker)
> +	if (args->user_worker) {
> +		/*
> +		 * User worker are similar to io_threads but they do not
> +		 * support signals and cleanup is driven via another kernel
> +		 * interface so even SIGKILL is blocked.
> +		 */
>  		p->flags |= PF_USER_WORKER;
> +		siginitsetinv(&p->blocked, 0);

I never liked the fact that io-threads block the signals, this adds
another precedent... OK, this needs another discussion.

> +static void try_set_pending_sigkill(struct task_struct *t)
> +{
> +	/*
> +	 * User workers don't support signals and their exit is driven through
> +	 * their kernel layer, so by default block even SIGKILL.
> +	 */
> +	if (sigismember(&t->blocked, SIGKILL))
> +		return;
> +
> +	sigaddset(&t->pending.signal, SIGKILL);
> +	signal_wake_up(t, 1);
> +}

so why do you need this? to avoid fatal_signal_pending() or signal_pending() ?

In the latter case this change is not enough.

Oleg.