posix-timers: check ->it_signal instead of ->it_pid to validate the timer
Oleg Nesterov [Mon, 1 Dec 2008 22:18:15 +0000 (14:18 -0800)]
Impact: clean up, speed up

->it_pid (was ->it_process) has also a special meaning: if it is NULL,
the timer is under deletion or it wasn't initialized yet. We can check
->it_signal != NULL instead, this way we can

- simplify sys_timer_create() a bit

- remove yet another check from lock_timer()

- move put_pid(->it_pid) into release_posix_timer() which
  runs outside of ->it_lock

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/posix-timers.c

index 42a39af..aa922bb 100644 (file)
@@ -464,6 +464,7 @@ static void release_posix_timer(struct k_itimer *tmr, int it_id_set)
                idr_remove(&posix_timers_id, tmr->it_id);
                spin_unlock_irqrestore(&idr_lock, flags);
        }
+       put_pid(tmr->it_pid);
        sigqueue_free(tmr->sigq);
        kmem_cache_free(posix_timers_cache, tmr);
 }
@@ -477,7 +478,6 @@ sys_timer_create(const clockid_t which_clock,
 {
        struct k_itimer *new_timer;
        int error, new_timer_id;
-       struct pid *it_pid;
        sigevent_t event;
        int it_id_set = IT_ID_NOT_SET;
 
@@ -531,9 +531,9 @@ sys_timer_create(const clockid_t which_clock,
                        goto out;
                }
                rcu_read_lock();
-               it_pid = get_pid(good_sigevent(&event));
+               new_timer->it_pid = get_pid(good_sigevent(&event));
                rcu_read_unlock();
-               if (!it_pid) {
+               if (!new_timer->it_pid) {
                        error = -EINVAL;
                        goto out;
                }
@@ -541,7 +541,7 @@ sys_timer_create(const clockid_t which_clock,
                event.sigev_notify = SIGEV_SIGNAL;
                event.sigev_signo = SIGALRM;
                event.sigev_value.sival_int = new_timer->it_id;
-               it_pid = get_pid(task_tgid(current));
+               new_timer->it_pid = get_pid(task_tgid(current));
        }
 
        new_timer->it_sigev_notify     = event.sigev_notify;
@@ -551,7 +551,6 @@ sys_timer_create(const clockid_t which_clock,
        new_timer->sigq->info.si_code  = SI_TIMER;
 
        spin_lock_irq(&current->sighand->siglock);
-       new_timer->it_pid = it_pid;
        new_timer->it_signal = current->signal;
        list_add(&new_timer->list, &current->signal->posix_timers);
        spin_unlock_irq(&current->sighand->siglock);
@@ -587,7 +586,7 @@ static struct k_itimer *lock_timer(timer_t timer_id, unsigned long *flags)
        timr = idr_find(&posix_timers_id, (int)timer_id);
        if (timr) {
                spin_lock(&timr->it_lock);
-               if (timr->it_pid && timr->it_signal == current->signal) {
+               if (timr->it_signal == current->signal) {
                        spin_unlock(&idr_lock);
                        return timr;
                }
@@ -834,8 +833,7 @@ retry_delete:
         * This keeps any tasks waiting on the spin lock from thinking
         * they got something (see the lock code above).
         */
-       put_pid(timer->it_pid);
-       timer->it_pid = NULL;
+       timer->it_signal = NULL;
 
        unlock_timer(timer, flags);
        release_posix_timer(timer, IT_ID_SET);
@@ -861,8 +859,7 @@ retry_delete:
         * This keeps any tasks waiting on the spin lock from thinking
         * they got something (see the lock code above).
         */
-       put_pid(timer->it_pid);
-       timer->it_pid = NULL;
+       timer->it_signal = NULL;
 
        unlock_timer(timer, flags);
        release_posix_timer(timer, IT_ID_SET);