Messages in this thread | | | Date | Mon, 4 Mar 2019 21:08:09 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v4 04/17] x86/split_lock: Align x86_capability to unsigned long to avoid split locked access |
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On Mon, Mar 04, 2019 at 11:15:12AM -0800, Fenghua Yu wrote: > On Mon, Mar 04, 2019 at 10:52:19AM -0800, Dave Hansen wrote: > > On 3/1/19 6:44 PM, Fenghua Yu wrote: > > > diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h > > > index 33051436c864..eb8ae701ef65 100644 > > > --- a/arch/x86/include/asm/processor.h > > > +++ b/arch/x86/include/asm/processor.h > > > @@ -93,7 +93,9 @@ struct cpuinfo_x86 { > > > __u32 extended_cpuid_level; > > > /* Maximum supported CPUID level, -1=no CPUID: */ > > > int cpuid_level; > > > - __u32 x86_capability[NCAPINTS + NBUGINTS]; > > > + /* Unsigned long alignment to avoid split lock in atomic bitmap ops */ > > > + __u32 x86_capability[NCAPINTS + NBUGINTS] > > > + __aligned(sizeof(unsigned long)); > > > > I think this also warrants a comment in the changelog about the > > alignment of 'struct cpuinfo_x86'. > > How about add "Depending on the starting address where GCC generates > for data of struct cpuinfo_x86, x86_capability[] may or may not align to > unsigned long...."?
Composite types inherit the strictest alignment of their members. Without that alignment hints would be utterly useless.
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