On Fri, Jan 08, 2021 at 01:31:56PM +0100, Borislav Petkov wrote:
> On Thu, Jan 07, 2021 at 09:08:44AM -0800, Paul E. McKenney wrote:
> > Some information is usually better than none. And I bet that failing
> > hardware is capable of all sorts of tricks at all sorts of levels. ;-)
>
> Tell me about it.
>
> > Updated patch below. Is this what you had in mind?
>
> Ok, so I've massaged it into the below locally while taking another
> detailed look. Made the pr_info pr_emerg and poked at the text more, as
> I do. :)
>
> Lemme know if something else needs to be adjusted, otherwise I'll queue
> it.
Looks good to me! I agree that your change to the pr_emerg() string is
much better than my original. And good point on your added comment,
plus it was fun to see that my original "holdouts" wording has not
completely vanished. ;-)
Thank you very much!!!
Thanx, Paul
> Thx.
>
> ---
> Author: Paul E. McKenney <paul...@kernel.org>
> Date: Wed Dec 23 17:04:19 2020 -0800
>
> x86/mce: Make mce_timed_out() identify holdout CPUs
>
> The
>
> "Timeout: Not all CPUs entered broadcast exception handler"
>
> message will appear from time to time given enough systems, but this
> message does not identify which CPUs failed to enter the broadcast
> exception handler. This information would be valuable if available,
> for example, in order to correlate with other hardware-oriented error
> messages.
>
> Add a cpumask of CPUs which maintains which CPUs have entered this
> handler, and print out which ones failed to enter in the event of a
> timeout.
>
> [ bp: Massage. ]
>
> Reported-by: Jonathan Lemon <b...@fb.com>
> Signed-off-by: Paul E. McKenney <paul...@kernel.org>
> Signed-off-by: Borislav Petkov <b...@suse.de>
> Tested-by: Tony Luck <tony.l...@intel.com>
> Link:
> https://lkml.kernel.org/r/20210106174102.GA23874@paulmck-ThinkPad-P72
>
> diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
> index 13d3f1cbda17..6c81d0998e0a 100644
> --- a/arch/x86/kernel/cpu/mce/core.c
> +++ b/arch/x86/kernel/cpu/mce/core.c
> @@ -877,6 +877,12 @@ static atomic_t mce_executing;
> */
> static atomic_t mce_callin;
>
> +/*
> + * Track which CPUs entered the MCA broadcast synchronization and which not
> in
> + * order to print holdouts.
> + */
> +static cpumask_t mce_missing_cpus = CPU_MASK_ALL;
> +
> /*
> * Check if a timeout waiting for other CPUs happened.
> */
> @@ -894,8 +900,12 @@ static int mce_timed_out(u64 *t, const char *msg)
> if (!mca_cfg.monarch_timeout)
> goto out;
> if ((s64)*t < SPINUNIT) {
> - if (mca_cfg.tolerant <= 1)
> + if (mca_cfg.tolerant <= 1) {
> + if (cpumask_and(&mce_missing_cpus, cpu_online_mask,
> &mce_missing_cpus))
> + pr_emerg("CPUs not responding to MCE broadcast
> (may include false positives): %*pbl\n",
> + cpumask_pr_args(&mce_missing_cpus));
> mce_panic(msg, NULL, NULL);
> + }
> cpu_missing = 1;
> return 1;
> }
> @@ -1006,6 +1016,7 @@ static int mce_start(int *no_way_out)
> * is updated before mce_callin.
> */
> order = atomic_inc_return(&mce_callin);
> + cpumask_clear_cpu(smp_processor_id(), &mce_missing_cpus);
>
> /*
> * Wait for everyone.
> @@ -1114,6 +1125,7 @@ static int mce_end(int order)
> reset:
> atomic_set(&global_nwo, 0);
> atomic_set(&mce_callin, 0);
> + cpumask_setall(&mce_missing_cpus);
> barrier();
>
> /*
> @@ -2712,6 +2724,7 @@ static void mce_reset(void)
> atomic_set(&mce_executing, 0);
> atomic_set(&mce_callin, 0);
> atomic_set(&global_nwo, 0);
> + cpumask_setall(&mce_missing_cpus);
> }
>
> static int fake_panic_get(void *data, u64 *val)
>
> --
> Regards/Gruss,
> Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette
