Commit 9bf7c324 authored by Eric W. Biederman's avatar Eric W. Biederman
Browse files

posix-cpu-timers: Extend rcu_read_lock removing task_struct references 



Now that the code stores of pid references it is no longer necessary
or desirable to take a reference on task_struct in __get_task_for_clock.

Instead extend the scope of rcu_read_lock and remove the reference
counting on struct task_struct entirely.

Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
parent bbd40fc4

kernel/time/posix-cpu-timers.c

+23 −20
Original line number Original line Diff line number Diff line
@@ -81,36 +81,36 @@ static struct task_struct *lookup_task(const pid_t pid, bool thread, 
}

}





static struct task_struct *__get_task_for_clock(const clockid_t clock,

static struct task_struct *__get_task_for_clock(const clockid_t clock,

						bool getref, bool gettime)

						bool gettime)

{

{

	const bool thread = !!CPUCLOCK_PERTHREAD(clock);

	const bool thread = !!CPUCLOCK_PERTHREAD(clock);

	const pid_t pid = CPUCLOCK_PID(clock);

	const pid_t pid = CPUCLOCK_PID(clock);

	struct task_struct *p;





	if (CPUCLOCK_WHICH(clock) >= CPUCLOCK_MAX)

	if (CPUCLOCK_WHICH(clock) >= CPUCLOCK_MAX)

		return NULL;

		return NULL;





	rcu_read_lock();

	return lookup_task(pid, thread, gettime);

	p = lookup_task(pid, thread, gettime);

	if (p && getref)

		get_task_struct(p);

	rcu_read_unlock();

	return p;

}

}





static inline struct task_struct *get_task_for_clock(const clockid_t clock)

static inline struct task_struct *get_task_for_clock(const clockid_t clock)

{

{

	return __get_task_for_clock(clock, true, false);

	return __get_task_for_clock(clock, false);

}

}





static inline struct task_struct *get_task_for_clock_get(const clockid_t clock)

static inline struct task_struct *get_task_for_clock_get(const clockid_t clock)

{

{

	return __get_task_for_clock(clock, true, true);

	return __get_task_for_clock(clock, true);

}

}





static inline int validate_clock_permissions(const clockid_t clock)

static inline int validate_clock_permissions(const clockid_t clock)

{

{

	return __get_task_for_clock(clock, false, false) ? 0 : -EINVAL;

	int ret;



	rcu_read_lock();

	ret = __get_task_for_clock(clock, false) ? 0 : -EINVAL;

	rcu_read_unlock();



	return ret;

}

}





static inline enum pid_type cpu_timer_pid_type(struct k_itimer *timer)

static inline enum pid_type cpu_timer_pid_type(struct k_itimer *timer)
@@ -368,15 +368,18 @@ static int posix_cpu_clock_get(const clockid_t clock, struct timespec64 *tp) 
	struct task_struct *tsk;

	struct task_struct *tsk;

	u64 t;

	u64 t;





	rcu_read_lock();

	tsk = get_task_for_clock_get(clock);

	tsk = get_task_for_clock_get(clock);

	if (!tsk)

	if (!tsk) {

		rcu_read_unlock();

		return -EINVAL;

		return -EINVAL;

	}





	if (CPUCLOCK_PERTHREAD(clock))

	if (CPUCLOCK_PERTHREAD(clock))

		t = cpu_clock_sample(clkid, tsk);

		t = cpu_clock_sample(clkid, tsk);

	else

	else

		t = cpu_clock_sample_group(clkid, tsk, false);

		t = cpu_clock_sample_group(clkid, tsk, false);

	put_task_struct(tsk);

	rcu_read_unlock();





	*tp = ns_to_timespec64(t);

	*tp = ns_to_timespec64(t);

	return 0;

	return 0;
@@ -389,19 +392,19 @@ static int posix_cpu_clock_get(const clockid_t clock, struct timespec64 *tp) 
 */

 */

static int posix_cpu_timer_create(struct k_itimer *new_timer)

static int posix_cpu_timer_create(struct k_itimer *new_timer)

{

{

	struct task_struct *p = get_task_for_clock(new_timer->it_clock);

	struct task_struct *p;





	if (!p)

	rcu_read_lock();

	p = get_task_for_clock(new_timer->it_clock);

	if (!p) {

		rcu_read_unlock();

		return -EINVAL;

		return -EINVAL;

	}





	new_timer->kclock = &clock_posix_cpu;

	new_timer->kclock = &clock_posix_cpu;

	timerqueue_init(&new_timer->it.cpu.node);

	timerqueue_init(&new_timer->it.cpu.node);

	new_timer->it.cpu.pid = get_task_pid(p, cpu_timer_pid_type(new_timer));

	new_timer->it.cpu.pid = get_task_pid(p, cpu_timer_pid_type(new_timer));

	/*

	rcu_read_unlock();

	 * get_task_for_clock() took a reference on @p. Drop it as the timer

	 * holds a reference on the pid of @p.

	 */

	put_task_struct(p);

	return 0;

	return 0;

}

}