linux-kernel - Re: [PATCH] kexec: Update vmcoreinfo after crash happened

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Date:   Thu, 16 Mar 2017 20:27:30 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Xunlei Pang <xlpang@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
        akpm@...ux-foundation.org, Eric Biederman <ebiederm@...ssion.com>,
        Dave Young <dyoung@...hat.com>
Subject: Re: [PATCH] kexec: Update vmcoreinfo after crash happened

Hi Xunlei,

Did you really see this ever happened? Because the vmcore size estimate
feature, namely --mem-usage option of makedumpfile, depends on the
vmcoreinfo in 1st kernel, your change will break it.

If not, it could be not good to change that.

Baoquan

On 03/16/17 at 08:16pm, Xunlei Pang wrote:
> Currently vmcoreinfo data is updated at boot time subsys_initcall(),
> it has the risk of being modified by some wrong code during system
> is running.
> 
> As a result, vmcore dumped will contain the wrong vmcoreinfo. Later on,
> when using "crash" utility to parse this vmcore, we probably will get
> "Segmentation fault".
> 
> Based on the fact that the value of each vmcoreinfo stays invariable
> once kernel boots up, we safely move all the vmcoreinfo operations into
> crash_save_vmcoreinfo() which is called after crash happened. In this
> way, vmcoreinfo data correctness is always guaranteed.
> 
> Signed-off-by: Xunlei Pang <xlpang@...hat.com>
> ---
>  kernel/kexec_core.c | 14 +++-----------
>  1 file changed, 3 insertions(+), 11 deletions(-)
> 
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index bfe62d5..1bfdd96 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -1367,12 +1367,6 @@ static void update_vmcoreinfo_note(void)
>  	final_note(buf);
>  }
>  
> -void crash_save_vmcoreinfo(void)
> -{
> -	vmcoreinfo_append_str("CRASHTIME=%ld\n", get_seconds());
> -	update_vmcoreinfo_note();
> -}
> -
>  void vmcoreinfo_append_str(const char *fmt, ...)
>  {
>  	va_list args;
> @@ -1402,7 +1396,7 @@ phys_addr_t __weak paddr_vmcoreinfo_note(void)
>  	return __pa_symbol((unsigned long)(char *)&vmcoreinfo_note);
>  }
>  
> -static int __init crash_save_vmcoreinfo_init(void)
> +void crash_save_vmcoreinfo(void)
>  {
>  	VMCOREINFO_OSRELEASE(init_uts_ns.name.release);
>  	VMCOREINFO_PAGESIZE(PAGE_SIZE);
> @@ -1474,13 +1468,11 @@ static int __init crash_save_vmcoreinfo_init(void)
>  #endif
>  
>  	arch_crash_save_vmcoreinfo();
> -	update_vmcoreinfo_note();
> +	vmcoreinfo_append_str("CRASHTIME=%ld\n", get_seconds());
>  
> -	return 0;
> +	update_vmcoreinfo_note();
>  }
>  
> -subsys_initcall(crash_save_vmcoreinfo_init);
> -
>  /*
>   * Move into place and start executing a preloaded standalone
>   * executable.  If nothing was preloaded return an error.
> -- 
> 1.8.3.1
>