Re: [PATCH][RT] x86: Fix an RT MCE crash

[Borislav Petkov <bp@alien8.de>]

+ Tony.

On Thu, Jun 30, 2016 at 11:51:01AM -0400, Steven Rostedt wrote:
> > >> From: Corey Minyard <cminyard@mvista.com>
> > >>
> > >> On some x86 systems an MCE interrupt would come in before the kernel
> > >> was ready for it.  Looking at the latest RT code, it has similar
> > >> (but not quite the same) code, except it adds a bool that tells if
> > >> MCE handling is initialized.  Add the same bool for older versions.
> > >>
> > >> Signed-off-by: Corey Minyard <cminyard@mvista.com>
> > >> ---
> > >>   arch/x86/kernel/cpu/mcheck/mce.c | 5 ++++-
> > >>   1 file changed, 4 insertions(+), 1 deletion(-)
> > >>
> > >> We noticed this issue on a new Broadwell system when we booted RT

Do you have any logs which hint at when exactly the MCE gets raised?

> > >> on it.  This patch is for 3.10, I'm not sure if it applies to
> > >> other kernel versions.  
> > > Do you mean other 'older' versions? and that this works with the
> > > versions after 3.10 without this patch?  
> > 
> > I haven't look at supported kernel versions besides 3.10 and 4.4.
> > The fix was from the 4.4 version of this code.  This patch fixes
> > v3.10-rt; I can look at finding which other versions need this.  I
> > was planning to do this, but I wanted to get the patch out for
> > comments first.
> 
> I'm not an MCE expert (I just Cc'd one though ;-)
> 
> OK, so you are saying that the fix was from 4.4-rt? I can go and look
> for it, and if so, I can add it to the "backport" patches I need to do.
> Which I need to go and do that soon (backport patches from previous
> versions). It may already be in that list.
> 
> -- Steve
> 
> > 
> > -corey
> > 
> > > -- Steve
> > >  
> > >> diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
> > >> index aaf4b9b..7125584 100644
> > >> --- a/arch/x86/kernel/cpu/mcheck/mce.c
> > >> +++ b/arch/x86/kernel/cpu/mcheck/mce.c
> > >> @@ -1365,6 +1365,7 @@ static void __mce_notify_work(void)
> > >>   }
> > >>   
> > >>   #ifdef CONFIG_PREEMPT_RT_FULL
> > >> +static bool notify_work_ready __read_mostly;
> > >>   struct task_struct *mce_notify_helper;
> > >>   
> > >>   static int mce_notify_helper_thread(void *unused)
> > >> @@ -1386,12 +1387,14 @@ static int mce_notify_work_init(void)

Hmm, what is mce_notify_work_init() ?

This must be some RT-homegrown thing.

What it is supposed to do? Upstream is much different from 3.10 or
whatever that kernel version is.

> > >>   	if (!mce_notify_helper)
> > >>   		return -ENOMEM;
> > >>   
> > >> +	notify_work_ready = true;
> > >>   	return 0;
> > >>   }
> > >>   
> > >>   static void mce_notify_work(void)

That is gone upstream too AFAICT.

> > >>   {
> > >> -	wake_up_process(mce_notify_helper);
> > >> +	if (notify_work_ready)
> > >> +		wake_up_process(mce_notify_helper);
> > >>   }
> > >>   #else
> > >>   static void mce_notify_work(void)  

Color me puzzled.

-- 
Regards/Gruss,
    Boris.

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