linux-kernel - Re: [PATCH] mm: Change return type to vm_fault

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Date:   Wed, 30 May 2018 09:10:47 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>, Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        zi.yan@...rutgers.edu,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Mark Rutland <mark.rutland@....com>, riel@...hat.com,
        pasha.tatashin@...cle.com, jschoenh@...zon.de,
        Kate Stewart <kstewart@...uxfoundation.org>,
        David Rientjes <rientjes@...gle.com>, tglx@...utronix.de,
        Peter Zijlstra <peterz@...radead.org>,
        Mel Gorman <mgorman@...e.de>, yang.s@...baba-inc.com,
        Minchan Kim <minchan@...nel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-kernel@...r.kernel.org, Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH] mm: Change return type to vm_fault_t

On Tue, May 29, 2018 at 11:04 PM, Matthew Wilcox <willy@...radead.org> wrote:
> On Tue, May 29, 2018 at 09:25:05PM +0530, Souptick Joarder wrote:
>> On Tue, May 29, 2018 at 8:20 PM, Matthew Wilcox <willy@...radead.org> wrote:
>> > On Tue, May 29, 2018 at 08:01:26PM +0530, Souptick Joarder wrote:
>> >> Use new return type vm_fault_t for fault handler. For
>> >> now, this is just documenting that the function returns
>> >> a VM_FAULT value rather than an errno. Once all instances
>> >> are converted, vm_fault_t will become a distinct type.
>> >
>> > I don't believe you've checked this with sparse.
>> >
>> >> @@ -802,7 +802,8 @@ int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
>> >>                    bool *unlocked)
>> >>  {
>> >>       struct vm_area_struct *vma;
>> >> -     int ret, major = 0;
>> >> +     int major = 0;
>> >> +     vm_fault_t ret;
>> >>
>> >>       if (unlocked)
>> >>               fault_flags |= FAULT_FLAG_ALLOW_RETRY;
>> >
>> > ...
>> >         major |= ret & VM_FAULT_MAJOR;
>> >
>> > That should be throwing a warning.
>>
>> Sorry, but I verified again and didn't see similar warnings.
>>
>> steps followed -
>>
>> apply the patch
>> make c=2 -j4 ( build for x86_64)
>> looking for warnings in files because of this patch.
>>
>> The only error I am seeing "error: undefined identifier '__COUNTER__' "
>> which is pointing to BUG(). There are few warnings but those are not
>> related to this patch.
>>
>> In my test tree the final patch to create new vm_fault_t type is
>> already applied.
>>
>> Do you want me to verify in some other way ?
>
> I see:
>
> mm/gup.c:817:15: warning: invalid assignment: |=
> mm/gup.c:817:15:    left side has type int
> mm/gup.c:817:15:    right side has type restricted vm_fault_t
>
> are you building with 'c=2' or 'C=2'?

Building with C=2.
Do I need to enable any separate FLAG ?