Re: [Xen-devel] [PATCH v3 1/9] x86/mce: handle LMCE locally

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 31.03.17 at 04:34, <haozhong.zhang@xxxxxxxxx> wrote:
> On 03/30/17 08:35 -0600, Jan Beulich wrote:
>> >>> On 30.03.17 at 08:19, <haozhong.zhang@xxxxxxxxx> wrote:
>> > --- a/xen/arch/x86/cpu/mcheck/mce.c
>> > +++ b/xen/arch/x86/cpu/mcheck/mce.c
>> > @@ -42,6 +42,13 @@ DEFINE_PER_CPU_READ_MOSTLY(struct mca_banks *, 
>> > poll_bankmask);
>> >  DEFINE_PER_CPU_READ_MOSTLY(struct mca_banks *, no_cmci_banks);
>> >  DEFINE_PER_CPU_READ_MOSTLY(struct mca_banks *, mce_clear_banks);
>> >  
>> > +/*
>> > + * Flag to indicate that at least one non-local MCE on this CPU has
>> > + * not been completed handled. It's set by mcheck_cmn_handler() and
>> > + * cleared by mce_softirq().
>> > + */
>> > +static DEFINE_PER_CPU(bool, nonlocal_mce_in_progress);
>> 
>> Does a boolean really suffice here? I.e. can't there be a 2nd one
>> while the first one is still being dealt with?
> 
> It's to indicate the existence of a non-local MCE, and mce_softirq()
> will call mctelem_process_deferred() to handle all MCE's if it's true,
> so a boolean flag is suffice.

I don't buy this, I'm sorry. What if a 2nd #MC occurs at the
instruction boundary of setting the variable to false (in
mce_softirq())? A subsequent mce_softirq() would then see
the variable being false, wouldn't it?

Jan


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