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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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