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Message-ID: <20211001122348.GB965@pathway.suse.cz>
Date: Fri, 1 Oct 2021 14:23:48 +0200
From: Petr Mladek <pmladek@...e.com>
To: Alexander Popov <alex.popov@...ux.com>
Cc: "Paul E. McKenney" <paulmck@...nel.org>,
	Jonathan Corbet <corbet@....net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Joerg Roedel <jroedel@...e.de>, Maciej Rozycki <macro@...am.me.uk>,
	Muchun Song <songmuchun@...edance.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Robin Murphy <robin.murphy@....com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Lu Baolu <baolu.lu@...ux.intel.com>,
	Kees Cook <keescook@...omium.org>,
	Luis Chamberlain <mcgrof@...nel.org>, Wei Liu <wl@....org>,
	John Ogness <john.ogness@...utronix.de>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Alexey Kardashevskiy <aik@...abs.ru>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Jann Horn <jannh@...gle.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mark Rutland <mark.rutland@....com>,
	Andy Lutomirski <luto@...nel.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Will Deacon <will.deacon@....com>,
	David S Miller <davem@...emloft.net>,
	Borislav Petkov <bp@...en8.de>, kernel-hardening@...ts.openwall.com,
	linux-hardening@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, notify@...nel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH] Introduce the pkill_on_warn boot parameter

On Thu 2021-09-30 18:05:54, Alexander Popov wrote:
> On 30.09.2021 12:15, Petr Mladek wrote:
> > On Wed 2021-09-29 12:49:24, Paul E. McKenney wrote:
> >> On Wed, Sep 29, 2021 at 10:01:33PM +0300, Alexander Popov wrote:
> >>> This patch was tested using CONFIG_LKDTM.
> >>> The kernel kills a process that performs this:
> >>>   echo WARNING > /sys/kernel/debug/provoke-crash/DIRECT
> >>>
> >>> If you are fine with this approach, I will prepare a patch adding the
> >>> pkill_on_warn sysctl.
> >>
> >> I suspect that you need a list of kthreads for which you are better
> >> off just invoking panic().  RCU's various kthreads, for but one set
> >> of examples.
> > 
> > I wonder if kernel could survive killing of any kthread. I have never
> > seen a code that would check whether a kthread was killed and
> > restart it.
> 
> The do_group_exit() function calls do_exit() from kernel/exit.c, which is also
> called during a kernel oops. This function cares about a lot of special cases
> depending on the current task_struct. Is it fine?

IMHO, the bigger problem is that nobody will start the kthreads again.
As a result, some kernel functionality will not longer work.

User space threads are different. The user/admin typically
have a chance to start them again.

We might get inspiration in OOM killer. It never kills kthreads
and the init process, see oom_unkillable_task().

It would be better to panic() when WARN() is called from a kthread
or the init process.

Best Regards,
Petr

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