linux-kernel - Re: [PATCH 2/8] selftests/vm: use a common gup

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Date:   Tue, 29 Sep 2020 14:55:24 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>,
        Jérôme Glisse <jglisse@...hat.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Shuah Khan <shuah@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-s390@...r.kernel.org
Subject: Re: [PATCH 2/8] selftests/vm: use a common gup_test.h

On Tue, Sep 29, 2020 at 10:44:31AM -0700, John Hubbard wrote:
> On 9/29/20 9:35 AM, Jason Gunthorpe wrote:
> > On Mon, Sep 28, 2020 at 01:10:24PM -0700, John Hubbard wrote:
> > > On 9/28/20 5:57 AM, Jason Gunthorpe wrote:
> > > > On Sun, Sep 27, 2020 at 11:21:53PM -0700, John Hubbard wrote:
> > > > > diff --git a/tools/testing/selftests/vm/Makefile b/tools/testing/selftests/vm/Makefile
> > > > > index d1ae706d9927..9cc6bc087461 100644
> > > > > +++ b/tools/testing/selftests/vm/Makefile
> > > > > @@ -130,3 +130,5 @@ endif
> > > > >    $(OUTPUT)/userfaultfd: LDLIBS += -lpthread
> > > > >    $(OUTPUT)/mlock-random-test: LDLIBS += -lcap
> > > > > +
> > > > > +$(OUTPUT)/gup_test: ../../../../mm/gup_test.h
> > > > 
> > > > There is no reason to do this, the auto depends will pick up header
> > > > files, and gup_test.h isn't a generated file
> > > > 
> 
> Oh, I misread your comment! You were talking about this Makefile
> dependency that I'm adding, rather than the ../'s in the path.
> 
> Well, for that though, it also has to stay as shown in this patch,
> because of this:
> 
> I don't see any "gcc -m" type of dependency generation pass happening
> in this relatively simple Make system. 

It happens with -MD, all the deps are stored in files like mm/.init-mm.o.cmd
and sucked into the build.

> And so, without including an explicit header file dependency (at
> least, that's the simplest way), changes to gup_test.h are not
> detected.

Shouldn't be

> Both the Makefile code and the observed behavior back this up. (I
> expect that this is because there is less use of header files in
> this area, because most unit tests are self-contained within a
> single .c file.)

Something else is very wrong then.

Jason