On 09/09, Eric W. Biederman wrote:
>
> This patch does several things.
> - The variables used are moved into a structure and declared in vt_kern.h
> - A spinlock is added so we don't have SMP races updating the values.
> - Instead of raw pid_t value a struct_pid is used to guard against
> pid wrap around issues, if the daemon to spawn a new console dies.
I am not arguing against this patch, but it's a pity we can't use 'struct pid'
lockless. What dou you think about this:
void delayed_free_pid(struct rcu_head *rhp)
{
struct pid *pid = container_of(rhp, struct pid, rcu);
kmem_cache_free(pid_cachep, pid);
}
void put_pid_rcu(struct pid *pid)
{
if (atomic_dec_and_test(&pid->count))
// this can happen only if delayed_put_pid()
// was already fired, we can re-use pid->rcu
call_rcu(&pid->rcu, delayed_free_pid);
}
Now,
update_pid()
{
// still needs some locking
put_pid_rcu(pid);
pid = get_pid(...);
}
use_pid()
{
rcu_read_lock();
do_something(pid);
rcu_read_unock();
}
Thoughts?
Oleg.
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