Re: [PATCH 02/10] mm: convert core mm to mm_flags_*() accessors

[Mateusz Guzik]

On Wed, Sep 17, 2025 at 1:57 AM Chris Mason <c...@meta.com> wrote:
>
> On Tue, 12 Aug 2025 16:44:11 +0100 Lorenzo Stoakes 
> <lorenzo.stoa...@oracle.com> wrote:
>
> > As part of the effort to move to mm->flags becoming a bitmap field, convert
> > existing users to making use of the mm_flags_*() accessors which will, when
> > the conversion is complete, be the only means of accessing mm_struct flags.
> >
> > This will result in the debug output being that of a bitmap output, which
> > will result in a minor change here, but since this is for debug only, this
> > should have no bearing.
> >
> > Otherwise, no functional changes intended.
> >
> > Signed-off-by: Lorenzo Stoakes <lorenzo.stoa...@oracle.com>
>
> [ ... ]
>
> > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > index 25923cfec9c6..17650f0b516e 100644
> > --- a/mm/oom_kill.c
> > +++ b/mm/oom_kill.c
>
> [ ... ]
>
> > @@ -1251,7 +1251,7 @@ SYSCALL_DEFINE2(process_mrelease, int, pidfd, 
> > unsigned int, flags)
> >        * Check MMF_OOM_SKIP again under mmap_read_lock protection to ensure
> >        * possible change in exit_mmap is seen
> >        */
> > -     if (!test_bit(MMF_OOM_SKIP, &mm->flags) && !__oom_reap_task_mm(mm))
> > +     if (mm_flags_test(MMF_OOM_SKIP, mm) && !__oom_reap_task_mm(mm))
> >               ret = -EAGAIN;
> >       mmap_read_unlock(mm);
> >
>
> Hi Lorzeno, I think we lost a ! here.
>
> claude found enough inverted logic in moved code that I did a new run with
> a more explicit prompt for it, but this was the only new hit.
>

I presume conversion was done mostly manually?

The way(tm) is to use coccinelle.

I whipped out the following real quick and results look good:

@@
expression mm, bit;
@@

- test_bit(bit, &mm->flags)
+ mm_flags_test(bit, mm)

$ spatch --sp-file mmbit.cocci mm/oom_kill.c
[snip]
@@ -892,7 +892,7 @@ static bool task_will_free_mem(struct ta
         * This task has already been drained by the oom reaper so there are
         * only small chances it will free some more
         */
-       if (test_bit(MMF_OOM_SKIP, &mm->flags))
+       if (mm_flags_test(MMF_OOM_SKIP, mm))
                return false;

        if (atomic_read(&mm->mm_users) <= 1)
@@ -1235,7 +1235,7 @@ SYSCALL_DEFINE2(process_mrelease, int, p
                reap = true;
        else {
                /* Error only if the work has not been done already */
-               if (!test_bit(MMF_OOM_SKIP, &mm->flags))
+               if (!mm_flags_test(MMF_OOM_SKIP, mm))
                        ret = -EINVAL;
        }
        task_unlock(p);
@@ -1251,7 +1251,7 @@ SYSCALL_DEFINE2(process_mrelease, int, p
         * Check MMF_OOM_SKIP again under mmap_read_lock protection to ensure
         * possible change in exit_mmap is seen
         */
-       if (!test_bit(MMF_OOM_SKIP, &mm->flags) && !__oom_reap_task_mm(mm))
+       if (!mm_flags_test(MMF_OOM_SKIP, mm) && !__oom_reap_task_mm(mm))
                ret = -EAGAIN;
        mmap_read_unlock(mm);