Re: [PATCH RFC] kexec: Freeze processes before kexec
On Thu, Nov 17, 2022 at 3:46 PM Philipp Rudo wrote:
> On Wed, 16 Nov 2022 15:16:10 -0500
> Steven Rostedt wrote:
>
> > On Wed, 16 Nov 2022 19:56:24 +
> > "Joel Fernandes (Google)" 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.
Indeed, sorry for my hasty comment and for misleading Steve. This is
seen to happen when doing manual kexec from the reboot(2) system call.
During a regular panic, machine_shutdown() is not called so this would
not happen. However, for testing, the crash is a hurdle.
> 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 a lot for your input. Rob, what do you think?
thanks,
- Joel
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Re: [PATCH RFC] kexec: Freeze processes before kexec
Hi Steve,
On Wed, 16 Nov 2022 15:16:10 -0500
Steven Rostedt wrote:
> On Wed, 16 Nov 2022 19:56:24 +
> "Joel Fernandes (Google)" 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
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Re: [PATCH RFC] kexec: Freeze processes before kexec
Hey Steve,
On Wed, Nov 16, 2022 at 8:15 PM Steven Rostedt wrote:
>
> On Wed, 16 Nov 2022 19:56:24 +
> "Joel Fernandes (Google)" 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.
I am OK with not checking the return of freeze_processes() and trying
to shut down anyway. Will re-spin after any other feedback.
Thanks,
- Joel
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Re: [PATCH RFC] kexec: Freeze processes before kexec
On Wed, 16 Nov 2022 19:56:24 +
"Joel Fernandes (Google)" 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.
-- Steve
> +
> kexec_in_progress = true;
> kernel_restart_prepare("kexec reboot");
> migrate_to_reboot_cpu();
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