linux-kernel - Re: [PATCH RFC] kexec: Freeze processes before kexec

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Message-ID: <20221117164612.65832e37@rotkaeppchen>
Date:   Thu, 17 Nov 2022 16:46:12 +0100
From:   Philipp Rudo <prudo@...hat.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        linux-kernel@...r.kernel.org, ribalda@...gle.com,
        zwisler@...gle.com, robdclark@...il.com,
        Eric Biederman <ebiederm@...ssion.com>,
        kexec@...ts.infradead.org
Subject: Re: [PATCH RFC] kexec: Freeze processes before kexec

Hi Steve,

On Wed, 16 Nov 2022 15:16:10 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Wed, 16 Nov 2022 19:56:24 +0000
> "Joel Fernandes (Google)" <joel@...lfernandes.org> wrote:
> 
> > --- a/kernel/kexec_core.c
> > +++ b/kernel/kexec_core.c
> > @@ -1175,6 +1175,12 @@ int kernel_kexec(void)
> >  	} else
> >  #endif
> >  	{
> > +		error = freeze_processes();
> > +		if (error) {
> > +			error = -EBUSY;
> > +			goto Unlock;
> > +		}  
> 
> If this is the path of a kernel panic, do we really want to check the
> return error of freeze_processes()? We are panicing, there's not much more
> we can do.

kernel_kexec isn't called during panic. We don't need to worry about it
here.

Having that said I think this is a problem in the device driver _not_
in kexec. In my opinion it's the job of the driver to prevent such
races during shutdown.

Thanks
Philipp