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SubjectRe: [PATCH 2/3] x86, MCE: Drop default decoding notifier
On Wed, Apr 13, 2011 at 10:01:22AM -0400, Prarit Bhargava wrote:
> On 04/13/2011 09:36 AM, Borislav Petkov wrote:
> > From: Borislav Petkov <borislav.petkov@amd.com>
> >
> > The default notifier doesn't make a lot of sense to call in the
> > correctable errors case. Drop it and emit the mcelog decoding hint only
> > in the uncorrectable errors case and when no notifier is registered.
> >
> > Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
> > ---
> > arch/x86/include/asm/mce.h | 4 ++--
> > arch/x86/kernel/cpu/mcheck/mce.c | 26 +++++++++-----------------
> > 2 files changed, 11 insertions(+), 19 deletions(-)
> >
>
> > +extern atomic_t mce_decoders;
> > +
>
> Boris,
>
> I don't think we need to do this. I think we can use the existing notifier chain tools to do this check for us ... *untested and uncompiled* patch below.
>
> * Print out human-readable details about the MCE error,
> > * (if the CPU has an implementation for that)
> > */
> > - atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, m);
> > + if (!atomic_read(&mce_decoders)) {
> > + pr_emerg(HW_ERR "No human readable MCE decoding support on this CPU type.\n");
> > + pr_emerg(HW_ERR "Run the above through 'mcelog --ascii' to decode.\n");
>
> I thought we didn't want these lines at all for CE errors?

This is the UC only case - we call print_mce() before we panic.

>
> > + } else
> > + atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, m);
> > }
> >
> > #define PANIC_TIMEOUT 5 /* 5 seconds */
> > @@ -589,7 +582,8 @@ void machine_check_poll(enum mcp_flags flags, mce_banks_t *b)
> > */
> > if (!(flags & MCP_DONTLOG) && !mce_dont_log_ce) {
> > mce_log(&m);
> > - atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, &m);
> > + if (atomic_read(&mce_decoders))
> > + atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, &m);
> > }
> >
> > /*
> > @@ -1721,8 +1715,6 @@ __setup("mce", mcheck_enable);
> >
> > int __init mcheck_init(void)
> > {
> > - atomic_notifier_chain_register(&x86_mce_decoder_chain, &mce_dec_nb);
> > -
> > mcheck_intel_therm_init();
> >
> > return 0;
>
> Again, this patch has not been tested or compiled against latest upstream. I
> have quickly tested it against RHEL6 (2.6.32,33,34,35,36,38,39 based) and
> confirmed that I don't see the messages for CEs. I have NOT fully tested to see what happens when I add in a "dummy" notifier to see if the messages are not printed.
>
> diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
> index 3385ea2..b10a1f4 100644
> --- a/arch/x86/kernel/cpu/mcheck/mce.c
> +++ b/arch/x86/kernel/cpu/mcheck/mce.c
> @@ -100,25 +100,12 @@ static int cpu_missing;
>
> /*
> * CPU/chipset specific EDAC code can register a notifier call here to print
> - * MCE errors in a human-readable form.
> + * MCE errors in a human-readable form. Notifiers must return NOTIFY_STOP
> + * upon completion.
> */
> ATOMIC_NOTIFIER_HEAD(x86_mce_decoder_chain);
> EXPORT_SYMBOL_GPL(x86_mce_decoder_chain);
>
> -static int default_decode_mce(struct notifier_block *nb, unsigned long val,
> - void *data)
> -{
> - pr_emerg(HW_ERR "No human readable MCE decoding support on this CPU type.\n");
> - pr_emerg(HW_ERR "Run the message through 'mcelog --ascii' to decode.\n");
> -
> - return NOTIFY_STOP;
> -}
> -
> -static struct notifier_block mce_dec_nb = {
> - .notifier_call = default_decode_mce,
> - .priority = -1,
> -};
> -
> /* MCA banks polled by the period polling timer for corrected events */
> DEFINE_PER_CPU(mce_banks_t, mce_poll_banks) = {
> [0 ... BITS_TO_LONGS(MAX_NR_BANKS)-1] = ~0UL
> @@ -212,6 +199,8 @@ void mce_log(struct mce *mce)
>
> static void print_mce(struct mce *m)
> {
> + int ret;
> +
> pr_emerg(HW_ERR "CPU %d: Machine Check Exception: %Lx Bank %d: %016Lx\n",
> m->extcpu, m->mcgstatus, m->bank, m->status);
>
> @@ -236,10 +225,13 @@ static void print_mce(struct mce *m)
> m->cpuvendor, m->cpuid, m->time, m->socketid, m->apicid);
>
> /*
> - * Print out human-readable details about the MCE error,
> - * (if the CPU has an implementation for that)
> + * Output a message if the CPU has human-readable information for
> + * unhandled UC errors
> */
> - atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, m);
> + ret = atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, &m);
> + if ((ret != NOTIFY_STOP) && (m->status & MCI_STATUS_UC))
> + pr_emerg(HW_ERR "Run the message through 'mcelog --ascii' "
> + "to decode.\n");

Yep, yours is actually nicer - the notifier returns NOTIFY_DONE if it
doesn't call any notifier calls on the chain so the first test should
suffice.

Let me update the patch add your S-O-B so you could give it a run.

Thanks.


--
Regards/Gruss,
Boris.

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