Re: [PATCH v6 5/6] MCS Lock: Restructure the MCS lock defines and locking code into its own file

Joe Perches
2013-09-27T14:05:10Z

On Fri, 2013-09-27 at 15:48 +0200, Peter Zijlstra wrote:
> On Fri, Sep 27, 2013 at 06:44:55AM -0700, Joe Perches wrote:
> > It's a CHK test, so it's only tested with --strict
> >
> > $ scripts/checkpatch.pl -f --strict kernel/mutex.c 2>&1 | grep memory
> > CHECK: memory barrier without comment
> > CHECK: memory barrier without comment
> >
> > It could be changed to WARN so it's always on.
>
> Yes please, we can't be too careful with memory barriers.

I'll send the patch separately.

It seems a pretty noisy test.
There are 13 hits just in arch/x86/kernel/

$ ./scripts/checkpatch.pl -f arch/x86/kernel/*.c | grep -A3 "memory barrier"
WARNING: memory barrier without comment
#685: FILE: x86/kernel/alternative.c:685:
+ smp_wmb();

--
WARNING: memory barrier without comment
#401: FILE: x86/kernel/kvm.c:401:
+ rmb();

WARNING: memory barrier without comment
#403: FILE: x86/kernel/kvm.c:403:
+ rmb();

--
WARNING: memory barrier without comment
#702: FILE: x86/kernel/kvm.c:702:
+ smp_wmb();

WARNING: memory barrier without comment
#704: FILE: x86/kernel/kvm.c:704:
+ smp_wmb();

--
WARNING: memory barrier without comment
#62: FILE: x86/kernel/ldt.c:62:
+ wmb();

WARNING: memory barrier without comment
#64: FILE: x86/kernel/ldt.c:64:
+ wmb();

--
WARNING: memory barrier without comment
#204: FILE: x86/kernel/smpboot.c:204:
+ wmb();

WARNING: memory barrier without comment
#265: FILE: x86/kernel/smpboot.c:265:
+ wmb();

--
WARNING: memory barrier without comment
#557: FILE: x86/kernel/smpboot.c:557:
+ mb();

--
WARNING: memory barrier without comment
#1065: FILE: x86/kernel/smpboot.c:1065:
+ mb();

--
WARNING: memory barrier without comment
#1321: FILE: x86/kernel/smpboot.c:1321:
+ mb();

WARNING: memory barrier without comment
#1399: FILE: x86/kernel/smpboot.c:1399:
+ mb();