On Fri, Jun 12, 2020 at 06:28:15PM +0800, Xiaoming Ni wrote:
> Cred release and usage check code flow:
> 1. put_cred()
> if (atomic_dec_and_test(&(cred)->usage))
> __put_cred(cred);
>
> 2. __put_cred()
> BUG_ON(atomic_read(&cred->usage) != 0);
> call_rcu(&cred->rcu, put_cred_rcu);
>
> 3. put_cred_rcu()
> if (atomic_read(&cred->usage) != 0)
> panic("CRED: put_cred_rcu() sees %p with usage %d\n",
> cred, atomic_read(&cred->usage));
> kmem_cache_free(cred_jar, cred);
>
> If panic is triggered on put_cred_rcu(), there are two possibilities
> 1. Call get_cred() after __put_cred(), usage > 0
> 2. Call put_cred() after __put_cred(), usage < 0
> Since put_cred_rcu is an asynchronous behavior, it is no longer the first
> scene when panic, there is no information about the murderer in the panic
> call stack...
>
> So, add WARN() in get_cred()/put_cred(), and pray to catch the murderer
> at the first scene.
Why not not use refcount_t? It has all that goodness and more.
