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SubjectRe: [PATCH] kernel/panic/kexec: fix "crash_kexec_post_notifiers" option issue in oops path
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Hello,

From: Baoquan He <bhe@redhat.com>
Subject: Re: [PATCH] kernel/panic/kexec: fix "crash_kexec_post_notifiers" option issue in oops path
Date: Mon, 9 Feb 2015 10:40:30 +0800

> On 02/05/15 at 05:59pm, 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@jp.fujitsu.com>
>> ---
>> 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;
>> if (in_interrupt() || !p->pid || is_global_init(p) || panic_on_oops)
>> return 1;
>
> What if these two conditions !p->pid || is_global_init(p) are satisfied?
> Seems the behavious is changed.
>

Please further follow do_exit() path. For each condition, there are
the corresponding panic() calls. In summary:

oops_end
1) panic() for in_interrupt()
2) panic() for panic_on_oops
do_exit
3) panic() for !p->pid (idle task)
exit_notify
forget_original_parent
find_child_reaper
4) panic() for p->pid == 1 (init task)

--
Thanks.
HATAYAMA, Daisuke



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