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

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: <20171101164314.GA32760@redhat.com>
Date:   Wed, 1 Nov 2017 17:43:14 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Miroslav Benes <mbenes@...e.cz>, jpoimboe@...hat.com,
        jeyu@...nel.org, jikos@...nel.org, lpechacek@...e.cz, pavel@....cz,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org
Subject: Re: [PATCH v3 1/2] livepatch: send a fake signal to all blocking
 tasks

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.