Messages in this thread | | | Date | Sun, 10 Sep 2006 18:29:42 +0400 | From | Oleg Nesterov <> | Subject | Re: [PATCH] vt: Rework the console spawning variables. |
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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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