Re: [PATCH] fs: handle shrinker registration failure in sget_userns

[Tetsuo Handa]

Michal Hocko wrote:
> > @@ -260,9 +261,8 @@ static struct super_block *alloc_super(struct 
> > file_system_type *type, int flags,
> >     s->s_shrink.count_objects = super_cache_count;
> >     s->s_shrink.batch = 1024;
> >     s->s_shrink.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE;
> > -   INIT_LIST_HEAD(&s->s_shrink.list);
> > -   return s;
> > -
> > +   if (register_shrinker(&s->s_shrink) == 0)
> > +           return s;
> >  fail:
> >     destroy_unused_super(s);
> >     return NULL;
> 
> But I am not sure this is correct. So what protects shrinker invocation
> while the object is not initialized yet?

Then, what protects shrinker invocation in your patch?
Your patch is calling register_shrinker() immediately after
alloc_super() succeeds. My patch just moved register_shrinker()
into alloc_super().

@@ -503,6 +512,10 @@ struct super_block *sget_userns(struct file_system_type 
*type,
                s = alloc_super(type, (flags & ~SB_SUBMOUNT), user_ns);
                if (!s)
                        return ERR_PTR(-ENOMEM);
+               if (register_shrinker(&s->s_shrink)) {
+                       destroy_unused_super(s);
+                       return ERR_PTR(-ENOMEM);
+               }
                goto retry;
        }