Re: [PATCH v4] md/raid5: fix atomicity violation in raid5_cache_count

On Thu, Jan 11, 2024 at 11:10 PM Gui-Dong Han 2045gemini@gmail.com wrote:

[...]

    raid5_release_stripe(sh);

•   conf->max_nr_stripes++;
  

•   WRITE_ONCE(conf->max_nr_stripes, conf->max_nr_stripes + 1);
  

This is weird. We are reading max_nr_stripes without READ_ONCE.

    return 1;

}

@@ -2707,7 +2707,7 @@ static int drop_one_stripe(struct r5conf *conf) shrink_buffers(sh); free_stripe(conf->slab_cache, sh); atomic_dec(&conf->active_stripes);

•   conf->max_nr_stripes--;
  

•   WRITE_ONCE(conf->max_nr_stripes, conf->max_nr_stripes - 1);
  

Same here.

    return 1;

}

@@ -6820,7 +6820,7 @@ raid5_set_cache_size(struct mddev *mddev, int size) if (size <= 16 || size > 32768) return -EINVAL;

•   conf->min_nr_stripes = size;
  

•   WRITE_ONCE(conf->min_nr_stripes, size);
    mutex_lock(&conf->cache_size_mutex);
    while (size < conf->max_nr_stripes &&
           drop_one_stripe(conf))
  

@@ -6832,7 +6832,7 @@ raid5_set_cache_size(struct mddev *mddev, int size) mutex_lock(&conf->cache_size_mutex); while (size > conf->max_nr_stripes) if (!grow_one_stripe(conf, GFP_KERNEL)) {

•                   conf->min_nr_stripes = conf->max_nr_stripes;
  

•                   WRITE_ONCE(conf->min_nr_stripes, conf->max_nr_stripes);
  

And here.

                    result = -ENOMEM;
                    break;
            }

Thanks, Song