Re: [PATCH v8 1/2] x86/kexec: add a new atomic notifier list for kdump

From: ebiederm@xmission.com (Eric W. Biederman)
To: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>,
	Gleb Natapov <gleb@redhat.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"x86@kernel.org" <x86@kernel.org>,
	"kexec@lists.infradead.org" <kexec@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v8 1/2] x86/kexec: add a new atomic notifier list for kdump
Date: Mon, 26 Nov 2012 09:08:54 -0600	[thread overview]
Message-ID: <87ip8sxuyh.fsf@xmission.com> (raw)
In-Reply-To: <50ADE11A.401@cn.fujitsu.com> (Zhang Yanfei's message of "Thu, 22 Nov 2012 16:23:54 +0800")

Zhang Yanfei <zhangyanfei@cn.fujitsu.com> writes:

> This patch adds an atomic notifier list named crash_notifier_list.
> Currently, when loading kvm-intel module, a notifier will be registered
> in the list to enable vmcss loaded on all cpus to be VMCLEAR'd if
> needed.

crash_notifier_list ick gag please no.  Effectively this makes the kexec
on panic code path undebuggable.

Instead we need to use direct function calls to whatever you are doing.

If a direct function call is too complex then the piece of code you want
to call is almost certainly too complex to be calling on a code path
like this.

Eric

> Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
> ---
>  arch/x86/include/asm/kexec.h |    2 ++
>  arch/x86/kernel/crash.c      |    9 +++++++++
>  2 files changed, 11 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
> index 317ff17..5e22b00 100644
> --- a/arch/x86/include/asm/kexec.h
> +++ b/arch/x86/include/asm/kexec.h
> @@ -163,6 +163,8 @@ struct kimage_arch {
>  };
>  #endif
>  
> +extern struct atomic_notifier_head crash_notifier_list;
> +
>  #endif /* __ASSEMBLY__ */
>  
>  #endif /* _ASM_X86_KEXEC_H */
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index 13ad899..c5b2f70 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -16,6 +16,8 @@
>  #include <linux/delay.h>
>  #include <linux/elf.h>
>  #include <linux/elfcore.h>
> +#include <linux/module.h>
> +#include <linux/notifier.h>
>  
>  #include <asm/processor.h>
>  #include <asm/hardirq.h>
> @@ -30,6 +32,9 @@
>  
>  int in_crash_kexec;
>  
> +ATOMIC_NOTIFIER_HEAD(crash_notifier_list);
> +EXPORT_SYMBOL_GPL(crash_notifier_list);
> +
>  #if defined(CONFIG_SMP) && defined(CONFIG_X86_LOCAL_APIC)
>  
>  static void kdump_nmi_callback(int cpu, struct pt_regs *regs)
> @@ -46,6 +51,8 @@ static void kdump_nmi_callback(int cpu, struct pt_regs *regs)
>  #endif
>  	crash_save_cpu(regs, cpu);
>  
> +	atomic_notifier_call_chain(&crash_notifier_list, 0, NULL);
> +
>  	/* Disable VMX or SVM if needed.
>  	 *
>  	 * We need to disable virtualization on all CPUs.
> @@ -88,6 +95,8 @@ void native_machine_crash_shutdown(struct pt_regs *regs)
>  
>  	kdump_nmi_shootdown_cpus();
>  
> +	atomic_notifier_call_chain(&crash_notifier_list, 0, NULL);
> +
>  	/* Booting kdump kernel with VMX or SVM enabled won't work,
>  	 * because (among other limitations) we can't disable paging
>  	 * with the virt flags.

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