[RFC PATCH] x86: Do not panic if mce=2 is passed

[RFC PATCH] x86: Do not panic if mce=2 is passed

[Yinghai Lu]

From: Yinghai Lu <yinghai.lu@oracle.com>

For UE recovery support, current we need mce=2 in command line
and also disable panic_on_oops with sysctl.

but other user may still need to have panic_on_oops to 1 always.

We can remove checking of panic_on_oops for mce-severity path.

We should be ok as on default path when mce=2 is not passed, tolerant
is 0, so they will still get MCE_PANIC_SEVERITY returned.

Signed-off-by: Yinghai Lu <yinghai.lu@oracle.com>


---
 arch/x86/kernel/cpu/mcheck/mce-severity.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6/arch/x86/kernel/cpu/mcheck/mce-severity.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/cpu/mcheck/mce-severity.c
+++ linux-2.6/arch/x86/kernel/cpu/mcheck/mce-severity.c
@@ -311,7 +311,7 @@ static int mce_severity_intel(struct mce
 			*msg = s->msg;
 		s->covered = 1;
 		if (s->sev >= MCE_UC_SEVERITY && ctx == IN_KERNEL) {
-			if (panic_on_oops || tolerant < 1)
+			if (tolerant < 1)
 				return MCE_PANIC_SEVERITY;
 		}
 		return s->sev;

RE: [RFC PATCH] x86: Do not panic if mce=2 is passed

[Luck, Tony]

> For UE recovery support, current we need mce=2 in command line
> and also disable panic_on_oops with sysctl.

Please explain. I've never given mce=2 on command line, and have
had my kernel recover from thousands of (injected) UE memory errors.

-Tony

Re: [RFC PATCH] x86: Do not panic if mce=2 is passed

[Borislav Petkov]

On Fri, Sep 16, 2016 at 08:28:44PM +0000, Luck, Tony wrote:
> > For UE recovery support, current we need mce=2 in command line
> > and also disable panic_on_oops with sysctl.
> 
> Please explain. I've never given mce=2 on command line, and have
> had my kernel recover from thousands of (injected) UE memory errors.

So frankly, that panic_on_oops doesn't make a whole lotta sense to me.

It is promoting MCEs with severity MCE_UC_SEVERITY and higher to a
panic.

So let's look at those:

	MCE_UC_SEVERITY,	- we don't do anything special in the kernel for
				those so just as well.
	MCE_AR_SEVERITY,	- those end up in the memory failure code if
				they're memory errors
	MCE_PANIC_SEVERITY,	- causes panic

so if anything, panic_on_oops shouldn't control the panicking behavior
as tolerant does that already:

	 * Tolerant levels:
	 * 0: always panic on uncorrected errors, log corrected errors
	 * 1: panic or SIGBUS on uncorrected errors, log corrected errors
	 * 2: SIGBUS or log uncorrected errors (if possible), log corr. errors
	 * 3: never panic or SIGBUS, log all errors (for testing only)

IOW, I think that patch makes sense but please doublecheck my logic
above first.

Thanks.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
--

Re: [RFC PATCH] x86: Do not panic if mce=2 is passed

[Borislav Petkov]

On Fri, Sep 16, 2016 at 01:23:25PM -0700, Yinghai Lu wrote:
> From: Yinghai Lu <yinghai.lu@oracle.com>
> 
> For UE recovery support, current we need mce=2 in command line
> and also disable panic_on_oops with sysctl.
> 
> but other user may still need to have panic_on_oops to 1 always.
> 
> We can remove checking of panic_on_oops for mce-severity path.
> 
> We should be ok as on default path when mce=2 is not passed, tolerant
> is 0, so they will still get MCE_PANIC_SEVERITY returned.
> 
> Signed-off-by: Yinghai Lu <yinghai.lu@oracle.com>
> 
> 
> ---
>  arch/x86/kernel/cpu/mcheck/mce-severity.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Index: linux-2.6/arch/x86/kernel/cpu/mcheck/mce-severity.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/kernel/cpu/mcheck/mce-severity.c
> +++ linux-2.6/arch/x86/kernel/cpu/mcheck/mce-severity.c
> @@ -311,7 +311,7 @@ static int mce_severity_intel(struct mce
>  			*msg = s->msg;
>  		s->covered = 1;
>  		if (s->sev >= MCE_UC_SEVERITY && ctx == IN_KERNEL) {
> -			if (panic_on_oops || tolerant < 1)
> +			if (tolerant < 1)
>  				return MCE_PANIC_SEVERITY;
>  		}
>  		return s->sev;

Applied,
thanks.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.

[tip:ras/core] x86/MCE: Do not look at panic_on_oops in the severity grading

[tip-bot for Yinghai Lu]

Commit-ID:  f5e886ef9b45a3dbfd42b054a13c755894ea8402
Gitweb:     http://git.kernel.org/tip/f5e886ef9b45a3dbfd42b054a13c755894ea8402
Author:     Yinghai Lu <yinghai.lu@oracle.com>
AuthorDate: Fri, 16 Sep 2016 13:23:25 -0700
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Tue, 8 Nov 2016 17:10:12 +0100

x86/MCE: Do not look at panic_on_oops in the severity grading

The MCE tolerance levels control whether we panic on a machine check or do
something else like generating a signal and logging error information. This
is controlled by the mce=<level> command line parameter.

However, if panic_on_oops is set, it will force a panic for such an MCE
even though the user didn't want to.

So don't check panic_on_oops in the severity grading anymore.

One of the use cases for that is recovery from uncorrectable errors with
mce=2.

 [ Boris: rewrite commit message. ]

Signed-off-by: Yinghai Lu <yinghai.lu@oracle.com>
Acked-by: Tony Luck <tony.luck@intel.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Cc: x86-ml <x86@kernel.org>
Link: http://lkml.kernel.org/r/20160916202325.4972-1-yinghai@kernel.org
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/kernel/cpu/mcheck/mce-severity.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce-severity.c b/arch/x86/kernel/cpu/mcheck/mce-severity.c
index 631356c..c7efbcf 100644
--- a/arch/x86/kernel/cpu/mcheck/mce-severity.c
+++ b/arch/x86/kernel/cpu/mcheck/mce-severity.c
@@ -311,7 +311,7 @@ static int mce_severity_intel(struct mce *m, int tolerant, char **msg, bool is_e
 			*msg = s->msg;
 		s->covered = 1;
 		if (s->sev >= MCE_UC_SEVERITY && ctx == IN_KERNEL) {
-			if (panic_on_oops || tolerant < 1)
+			if (tolerant < 1)
 				return MCE_PANIC_SEVERITY;
 		}
 		return s->sev;