[PATCH] Only allow to set crash_kexec_post_notifiers on boot time

[Konrad Rzeszutek Wilk]

On Fri, Sep 18, 2020 at 05:47:43PM -0700, Andrew Morton wrote:
> On Fri, 18 Sep 2020 11:25:46 +0800 Dave Young <dyoung at redhat.com> wrote:
> 
> > crash_kexec_post_notifiers enables running various panic notifier
> > before kdump kernel booting. This increases risks of kdump failure.
> > It is well documented in kernel-parameters.txt. We do not suggest
> > people to enable it together with kdump unless he/she is really sure.
> > This is also not suggested to be enabled by default when users are
> > not aware in distributions.
> > 
> > But unfortunately it is enabled by default in systemd, see below
> > discussions in a systemd report, we can not convince systemd to change
> > it:
> > https://github.com/systemd/systemd/issues/16661
> > 
> > Actually we have got reports about kdump kernel hangs in both s390x
> > and powerpcle cases caused by the systemd change,  also some x86 cases
> > could also be caused by the same (although that is in Hyper-V code
> > instead of systemd, that need to be addressed separately).

Perhaps it may be better to fix the issus on s390x and PowerPC as well?

> > 
> > Thus to avoid the auto enablement here just disable the param writable
> > permission in sysfs.
> > 
> 
> Well.  I don't think this is at all a desirable way of resolving a
> disagreement with the systemd developers
> 
> At the above github address I'm seeing "ryncsn added a commit to
> ryncsn/systemd that referenced this issue 9 days ago", "pstore: don't
> enable crash_kexec_post_notifiers by default".  So didn't that address
> the issue?

It does in systemd, but there is a strong interest in making this on by default.