Re: [PATCH] Introduce the pkill_on_warn boot parameter

[Petr Mladek]

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