Re: [PATCH v3 1/2] livepatch: send a fake signal to all blocking tasks

From: Oleg Nesterov <oleg@redhat.com>
To: Petr Mladek <pmladek@suse.com>
Cc: Miroslav Benes <mbenes@suse.cz>,
	jpoimboe@redhat.com, jeyu@kernel.org, jikos@kernel.org,
	lpechacek@suse.cz, pavel@ucw.cz, live-patching@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Michael Ellerman <mpe@ellerman.id.au>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	Andy Lutomirski <luto@kernel.org>,
	linuxppc-dev@lists.ozlabs.org, x86@kernel.org
Subject: Re: [PATCH v3 1/2] livepatch: send a fake signal to all blocking tasks
Date: Wed, 1 Nov 2017 17:43:14 +0100	[thread overview]
Message-ID: <20171101164314.GA32760@redhat.com> (raw)
In-Reply-To: <20171101151355.GG20040@pathway.suse.cz>

On 11/01, Petr Mladek wrote:
>
> On Tue 2017-10-31 12:48:52, Miroslav Benes wrote:
> > +		if (task->flags & PF_KTHREAD) {
> > +			/*
> > +			 * Wake up a kthread which still has not been migrated.
> > +			 */
> > +			wake_up_process(task);
>
> I have just noticed that freezer used wake_up_state(p, TASK_INTERRUPTIBLE);
> IMHO, we should do so as well.

I won't argue, but...

> wake_up_process() wakes also tasks in TASK_UNINTERRUPTIBLE state.
> These might not be ready for an unexpected wakeup. For example,
> see concat_dev_erase() in drivers/mtd/mtdcontact.c.

I'd say that concat_dev_erase() should be fixed, any code should be ready
for spurious wakeup.

Note also that wake_up_state(TASK_INTERRUPTIBLE) won't wakeup the TASK_IDLE
kthreads, and most of the kthreads which use TASK_INTERRUPTIBLE should use
TASK_IDLE today, because in most cases TASK_INTERRUPTIBLE was used to not
contribute to loadavg.

Oleg.