linux-kernel - Re: [PATCH] RAS/CEC: Add debugfs switch to disable at run time

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Date:   Sat, 20 Apr 2019 11:18:46 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Tony Luck <tony.luck@...el.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] RAS/CEC: Add debugfs switch to disable at run time

On Sat, Apr 20, 2019 at 2:13 AM Borislav Petkov <bp@...en8.de> wrote:
>
> On Fri, Apr 19, 2019 at 10:43:03PM -0700, Cong Wang wrote:
> > With this change, although not even compiled, mcelog should still
> > receive correctable memory errors like before, even when we have
> > CONFIG_RAS_CEC=y.
> >
> > Does this make any sense to you?
>
> Yes, the answer is in the mail you snipped. Did you read it?

I read it, all of your response is based on your speculation that I
don't have CONFIG_X86_MCELOG_LEGACY=y, which is clearly
a misunderstanding.

You didn't answer my question here, because I asked you whether
the following change (PoC only) makes sense:

@ -567,12 +567,12 @@ static int mce_first_notifier(struct
notifier_block *nb, unsigned long val,
                              void *data)
 {
        struct mce *m = (struct mce *)data;
+       bool consumed;

        if (!m)
                return NOTIFY_DONE;

-       if (cec_add_mce(m))
-               return NOTIFY_STOP;
+       consumed = cec_add_mce(m);

        /* Emit the trace record: */
        trace_mce_record(m);
@@ -581,7 +581,7 @@ static int mce_first_notifier(struct
notifier_block *nb, unsigned long val,

        mce_notify_irq();

-       return NOTIFY_DONE;
+       return consumed ? NOTIFY_STOP : NOTIFY_DONE;
 }

>
> Hint: disable CONFIG_RAS_CEC.

I knew disabling it could cure the problem from the beginning, please
save your own time by not repeating things we both already knew. :)

Once again, I still don't think it is the right answer, which is also why I
keep finding different solutions. I know you disagree, but you never explain
why you disagree, you speculated CONFIG_X86_MCELOG_LEGACY,
which is completely a misunderstanding.

I brought up CONFIG_X86_MCELOG_LEGACY simply to show you
how we could break mcelog _LOUDLY_ if we really decide to break it,
currently it just breaks silently. You misinterpret it as if I understand
CONFIG_RAS as a replacement for CONFIG_X86_MCELOG_LEGACY,
which is a very sad misunderstanding.

Thanks.