Re: [PATCH v1] mm/shrinker: simplify shrinker_memcg_alloc() using guard()

[wangxuewen]

Hi,Muchun Song,

Thanks for your review.
I've updated the patch to v2 following your suggestions.

This change is only a local cleanup for this specific function, not part 
of any large-scale conversion to use the guard() mechanism.

Please review v2, thank you.

在 2026/5/12 17:10, Muchun Song 写道:
> > On May 12, 2026, at 16:55, wangxuewen <18810879172@xxxxxxx> wrote:
> >
> > Use guard(mutex) to automatically handle shrinker_mutex locking and
> > unlocking in shrinker_memcg_alloc(). This removes the explicit
> > mutex_unlock() call, the goto-based error path, and the redundant
> > ret variable, resulting in cleaner and more concise code.
> >
> > Signed-off-by: wangxuewen <wangxuewen@xxxxxxxxxx>
> > ---
> > mm/shrinker.c | 11 ++++-------
> > 1 file changed, 4 insertions(+), 7 deletions(-)
> >
> > diff --git a/mm/shrinker.c b/mm/shrinker.c
> > index 76b3f750cf65..1274130323bf 100644
> > --- a/mm/shrinker.c
> > +++ b/mm/shrinker.c
> > @@ -222,22 +222,19 @@ static int shrinker_memcg_alloc(struct shrinker *shrinker)
> > if (mem_cgroup_kmem_disabled() && !(shrinker->flags & SHRINKER_NONSLAB))
> > return -ENOSYS;
> >
> > - 	mutex_lock(&shrinker_mutex);
> > + 	guard(mutex)(&shrinker_mutex);
> > 	id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
> > 	if (id < 0)
> > - 		goto unlock;
> > + 	return id;
> >
> > 	if (id >= shrinker_nr_max) {
> > 		if (expand_shrinker_info(id)) {
> > 			idr_remove(&shrinker_idr, id);
> > - 			goto unlock;
> > + 			return -ENOMEM;
> > 		}
> > 	}
> > 	shrinker->id = id;
> > - 	ret = 0;
> > -unlock:
> > - 	mutex_unlock(&shrinker_mutex);
> > - 	return ret;
>
> One small thing: since ret is no longer used after this change,
> it should be dropped from the declaration to avoid an unused-variable
> warning:
>
>      -       int id, ret = -ENOMEM;
>      +       int id;
>
> Otherwise looks good to me.
>
> Thanks,
> Muchun
>
> > + 	return 0;
> > }
> >
> > static void shrinker_memcg_remove(struct shrinker *shrinker)
> > --
> > 2.25.1