Re: [RESEND PATCH] kernel/panic/kexec: fix "crash_kexec_post_notifiers" option issue in oops path

[HATAYAMA Daisuke]

From: Vivek Goyal <vgoyal@xxxxxxxxxx>
Subject: Re: [RESEND PATCH] kernel/panic/kexec: fix "crash_kexec_post_notifiers" option issue in oops path
Date: Thu, 5 Mar 2015 17:22:04 -0500

> On Thu, Mar 05, 2015 at 05:19:30PM -0500, Vivek Goyal wrote:
>> On Wed, Mar 04, 2015 at 05:56:48PM +0900, HATAYAMA Daisuke wrote:
>> > The commit f06e5153f4ae2e2f3b0300f0e260e40cb7fefd45 introduced
>> > "crash_kexec_post_notifiers" kernel boot option, which toggles
>> > wheather panic() calls crash_kexec() before or after panic_notifiers
>> > and dump kmsg.
>> > 
>> > The problem is that the commit overlooks panic_on_oops kernel boot
>> > option. If it is enabled, crash_kexec() is called directly without
>> > going through panic() in oops path.
>> > 
>> > To fix this issue, this patch adds a check to
>> > "crash_kexec_post_notifiers" in the condition of kexec_should_crash().
>> > 
>> > Signed-off-by: HATAYAMA Daisuke <d.hatayama@xxxxxxxxxxxxxx>
>> > Acked-by: Baoquan He <bhe@xxxxxxxxxx>
>> > Tested-by: Hidehiro Kawai <hidehiro.kawai.ez@xxxxxxxxxxx>
>> > ---
>> >  include/linux/kernel.h | 3 +++
>> >  kernel/kexec.c         | 2 ++
>> >  kernel/panic.c         | 2 +-
>> >  3 files changed, 6 insertions(+), 1 deletion(-)
>> > 
>> > diff --git a/include/linux/kernel.h b/include/linux/kernel.h
>> > index 64ce58b..f47379f 100644
>> > --- a/include/linux/kernel.h
>> > +++ b/include/linux/kernel.h
>> > @@ -426,6 +426,9 @@ extern int panic_on_unrecovered_nmi;
>> >  extern int panic_on_io_nmi;
>> >  extern int panic_on_warn;
>> >  extern int sysctl_panic_on_stackoverflow;
>> > +
>> > +extern bool crash_kexec_post_notifiers;
>> > +
>> >  /*
>> >   * Only to be used by arch init code. If the user over-wrote the default
>> >   * CONFIG_PANIC_TIMEOUT, honor it.
>> > diff --git a/kernel/kexec.c b/kernel/kexec.c
>> > index 9a8a01a..0ecf252 100644
>> > --- a/kernel/kexec.c
>> > +++ b/kernel/kexec.c
>> > @@ -84,6 +84,8 @@ struct resource crashk_low_res = {
>> >  
>> >  int kexec_should_crash(struct task_struct *p)
>> >  {
>> > +	if (crash_kexec_post_notifiers)
>> > +		return 0;
>> 
>> This is little confusing. So if crash_kexec_post_notifiers is set but
>> panic_on_oops is not set, still we will return?
>> 
>> Should we do this only if panic_on_oops is set? IOW, how about following
>> 
>> 	if (panic_on_oops && crash_kexec_post_notifiers)
>> 		return 0;
>> 
>> And then also put a comment explaining the rationale.
> 
> Ok, I went through the previous version of patch and discussion there
> which says that all the 4 conditions lead to panic. So putting above
> code should be fine.
> 
> Can you please atleast put a comment here to explain it as it was not
> obvious. Just mention that all the checks below lead to panic hence
> if user wants to run panic notifiers then don't run crash_kexec() yet.
> It will be run after panic notifiers.
> 

Thanks for your reviewing.

Yes, I'll put such new comment in the patch of next version.

--
Thanks.
HATAYAMA, Daisuke

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