Re: [RFC PATCH v2 1/8] Use atomic type for ucounts reference counting

[Eric W. Biederman]

Alexey Gladkov <gladkov.ale...@gmail.com> writes:

We might want to use refcount_t instead of atomic_t.  Not a big deal
either way.

> Signed-off-by: Alexey Gladkov <gladkov.ale...@gmail.com>
> ---
>  include/linux/user_namespace.h |  2 +-
>  kernel/ucount.c                | 10 +++++-----
>  2 files changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
> index 64cf8ebdc4ec..84fefa9247c4 100644
> --- a/include/linux/user_namespace.h
> +++ b/include/linux/user_namespace.h
> @@ -92,7 +92,7 @@ struct ucounts {
>       struct hlist_node node;
>       struct user_namespace *ns;
>       kuid_t uid;
> -     int count;
> +     atomic_t count;
>       atomic_t ucount[UCOUNT_COUNTS];
>  };
>  
> diff --git a/kernel/ucount.c b/kernel/ucount.c
> index 11b1596e2542..0f2c7c11df19 100644
> --- a/kernel/ucount.c
> +++ b/kernel/ucount.c
> @@ -141,7 +141,8 @@ static struct ucounts *get_ucounts(struct user_namespace 
> *ns, kuid_t uid)
>  
>               new->ns = ns;
>               new->uid = uid;
> -             new->count = 0;
> +
> +             atomic_set(&new->count, 0);
>  
>               spin_lock_irq(&ucounts_lock);
>               ucounts = find_ucounts(ns, uid, hashent);
> @@ -152,10 +153,10 @@ static struct ucounts *get_ucounts(struct 
> user_namespace *ns, kuid_t uid)
>                       ucounts = new;
>               }
>       }
> -     if (ucounts->count == INT_MAX)
> +     if (atomic_read(&ucounts->count) == INT_MAX)
>               ucounts = NULL;
>       else
> -             ucounts->count += 1;
> +             atomic_inc(&ucounts->count);
>       spin_unlock_irq(&ucounts_lock);
>       return ucounts;
>  }
> @@ -165,8 +166,7 @@ static void put_ucounts(struct ucounts *ucounts)
>       unsigned long flags;
>  
>       spin_lock_irqsave(&ucounts_lock, flags);
> -     ucounts->count -= 1;
> -     if (!ucounts->count)
> +     if (atomic_dec_and_test(&ucounts->count))
>               hlist_del_init(&ucounts->node);
>       else
>               ucounts = NULL;


This can become:
static void put_ucounts(struct ucounts *ucounts)
{
        unsigned long flags;

        if (atomic_dec_and_lock_irqsave(&ucounts->count, &ucounts_lock, flags)) 
{
                hlist_del_init(&ucounts->node);
                spin_unlock_irqrestore(&ucounts_lock);
                kfree(ucounts);
        }
}