Re: [PATCH 6/7] selftests: only compile userfaultfd for x86 and powperpc

[Andrea Arcangeli]

On Tue, Sep 08, 2015 at 08:25:45PM +0800, Bamvor Zhang Jian wrote:
> Hi, Michael
> 
> On 09/08/2015 05:54 PM, Michael Ellerman wrote:
> > On Tue, 2015-09-08 at 17:15 +0800, Bamvor Zhang Jian wrote:
> >> Hi, Michael
> >>
> >> I thought I reply to you, but ...
> >>
> >> On 08/31/2015 11:26 AM, Michael Ellerman wrote:
> >>> On Fri, 2015-08-14 at 21:43 +0800, Bamvor Jian Zhang wrote:
> >>>> Signed-off-by: Bamvor Jian Zhang <bamvor.zhangjian@xxxxxxxxxx>
> >>>> ---
> >>>>  tools/testing/selftests/vm/Makefile | 12 ++++++++++++
> >>>>  1 file changed, 12 insertions(+)
> >>>>
> >>>> diff --git a/tools/testing/selftests/vm/Makefile b/tools/testing/selftests/vm/Makefile
> >>>> index bb888c6..4dd6e4f 100644
> >>>> --- a/tools/testing/selftests/vm/Makefile
> >>>> +++ b/tools/testing/selftests/vm/Makefile
> >>>> @@ -1,5 +1,15 @@
> >>>>  # Makefile for vm selftests
> >>>>  
> >>>> +uname_M := $(shell uname -m 2>/dev/null || echo not)
> >>>> +ARCH ?= $(shell echo $(uname_M) | sed -e s/i.86/i386/ -e s/ppc.*/powerpc/)
> >>>> +
> >>>> +ifeq ($(ARCH),powerpc)
> >>>> +support_userfaultfd = yes
> >>>> +endif
> >>>> +ifeq ($(ARCH),x86)
> >>>> +support_userfaultfd = yes
> >>>> +endif
> >>>> +
> >>>>  CFLAGS = -Wall
> >>>>  BINARIES = compaction_test
> >>>>  BINARIES += hugepage-mmap
> >>>> @@ -9,7 +19,9 @@ BINARIES += mlock2-tests
> >>>>  BINARIES += on-fault-limit
> >>>>  BINARIES += thuge-gen
> >>>>  BINARIES += transhuge-stress
> >>>> +ifdef support_userfaultfd
> >>>>  BINARIES += userfaultfd
> >>>> +endif
> >>>>  
> >>>>  all: $(BINARIES)
> >>>>  %: %.c
> >>>
> >>>
> >>> This is nasty. It means when userfaultfd gets implemented for other arches
> >>> someone has to remember to update the logic here, which they won't.
> >>>
> >>> Instead the C program should just do nothing when __NR_userfaultfd is not defined, eg:
> >>>
> >>> #ifdef __NR_userfaultfd
> >>>
> >>> int main(int argc, char **argv)
> >>> {
> >>> 	...
> >>> }
> >>>
> >>> #else
> >>>
> >>> int main(void)
> >>> {
> >>> 	printf("skip: Skipping userfaultfd test\n");
> >>> 	return 0;
> >>> }
> >>> #endif
> >>>
> >>>
> >>> This way when the syscall is implemented for other arches the test will just
> >>> start working.
> >>>
> >>> cheers
> >>>
> >>>
> >> When read the following code, It seems that sometimes __NR_userfaultfd is not
> >> defined but the syscall is exist. I am not sure why these piece is needed.
> >> cc'd c
> >>
> >> #ifndef __NR_userfaultfd
> >> #ifdef __x86_64__
> >> #define __NR_userfaultfd 323
> >> #elif defined(__i386__)
> >> #define __NR_userfaultfd 374
> >> #elif defined(__powewrpc__)
> >> #define __NR_userfaultfd 364
> >> #else
> >> #error "missing __NR_userfaultfd definition"
> >> #endif
> >> #endif
> >>
> >> Do you mean that we should remove the above code?
> > 
> > Well yes, it would need to be removed to make the logic I suggested work.
> > 
> > I'm not sure those #defines actually help in practice, because if the syscall
> > number is not defined then linux/userfaultfd.h will not exist and the whole
> > test will not compile anyway.
> > 
> > I was suggesting something like this, which has the properties of:
> >  - not breaking the build on arches that don't have the syscall
> >  - still printing a notice on arches that don't have the syscall, both at build
> >    time and runtime.
> >  - building correctly on an arch as soon as that arch implements the syscall,
> >    with no extra changes required.
> Ok, I agree with you. I will send the updated patch later.

I already had a few minor changes queued to be submitted for arm and
ppc and a few updates to the selftest.

I didn't like that you had to remember running make headers_install
for changes like the below one to build, so I added the dependency so
that "make" still works without having to run other commands before
it. These aren't reviewed yet.

https://git.kernel.org/cgit/linux/kernel/git/andrea/aa.git/commit/?id=5ce2efeb91b501aa1bc7370f43732681fa9123e2

I was planning to send these non-x86 updates to Andrew for review and
merging...

Isn't this necessary as well?

https://git.kernel.org/cgit/linux/kernel/git/andrea/aa.git/commit/?id=0eb943b76537a93fc4dd85cc0cbf937ce8266228

I can include the below one too, but we need to coordinate to submit
them or eventually some will reject.


> > cheers
> > 
> > 
> > diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
> > index 2bf1fc3f562b..652c9d805006 100644
> > --- a/tools/testing/selftests/vm/userfaultfd.c
> > +++ b/tools/testing/selftests/vm/userfaultfd.c
> > @@ -64,19 +64,10 @@
> >  #include <sys/syscall.h>
> >  #include <sys/ioctl.h>
> >  #include <pthread.h>
> > -#include <linux/userfaultfd.h>
> >  
> > -#ifndef __NR_userfaultfd
> > -#ifdef __x86_64__
> > -#define __NR_userfaultfd 323
> > -#elif defined(__i386__)
> > -#define __NR_userfaultfd 374
> > -#elif defined(__powewrpc__)
> > -#define __NR_userfaultfd 364
> > -#else
> > -#error "missing __NR_userfaultfd definition"
> > -#endif
> > -#endif
> > +#ifdef __NR_userfaultfd
> > +
> > +#include <linux/userfaultfd.h>
> >  
> >  static unsigned long nr_cpus, nr_pages, nr_pages_per_cpu, page_size;
> >  
> > @@ -636,3 +627,15 @@ int main(int argc, char **argv)
> >  	       nr_pages, nr_pages_per_cpu);
> >  	return userfaultfd_stress();
> >  }
> > +
> > +#else /* ! __NR_userfaultfd */
> > +
> > +#warning "missing __NR_userfaultfd definition"
> > +
> > +int main(void)
> > +{
> > +	printf("skip: Skipping userfaultfd test (missing __NR_userfaultfd)\n");
> > +	return 0;
> > +}
> > +
> > +#endif
> > 
> > 
> 
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