diff options
| -rw-r--r-- | include/linux/posix-timers.h | 17 | ||||
| -rw-r--r-- | kernel/time/posix-cpu-timers.c | 81 | ||||
| -rw-r--r-- | kernel/time/posix-timers.c | 4 |
3 files changed, 82 insertions, 20 deletions
diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h index 2c6e99ca48af..d607f51404fc 100644 --- a/include/linux/posix-timers.h +++ b/include/linux/posix-timers.h @@ -4,6 +4,7 @@ #include <linux/spinlock.h> #include <linux/list.h> +#include <linux/mutex.h> #include <linux/alarmtimer.h> #include <linux/timerqueue.h> @@ -62,16 +63,18 @@ static inline int clockid_to_fd(const clockid_t clk) * cpu_timer - Posix CPU timer representation for k_itimer * @node: timerqueue node to queue in the task/sig * @head: timerqueue head on which this timer is queued - * @task: Pointer to target task + * @pid: Pointer to target task PID * @elist: List head for the expiry list * @firing: Timer is currently firing + * @handling: Pointer to the task which handles expiry */ struct cpu_timer { - struct timerqueue_node node; - struct timerqueue_head *head; - struct pid *pid; - struct list_head elist; - int firing; + struct timerqueue_node node; + struct timerqueue_head *head; + struct pid *pid; + struct list_head elist; + int firing; + struct task_struct __rcu *handling; }; static inline bool cpu_timer_enqueue(struct timerqueue_head *head, @@ -135,10 +138,12 @@ struct posix_cputimers { /** * posix_cputimers_work - Container for task work based posix CPU timer expiry * @work: The task work to be scheduled + * @mutex: Mutex held around expiry in context of this task work * @scheduled: @work has been scheduled already, no further processing */ struct posix_cputimers_work { struct callback_head work; + struct mutex mutex; unsigned int scheduled; }; diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c index 2f5e9b34022c..e9c6f9d0e42c 100644 --- a/kernel/time/posix-cpu-timers.c +++ b/kernel/time/posix-cpu-timers.c @@ -846,6 +846,8 @@ static u64 collect_timerqueue(struct timerqueue_head *head, return expires; ctmr->firing = 1; + /* See posix_cpu_timer_wait_running() */ + rcu_assign_pointer(ctmr->handling, current); cpu_timer_dequeue(ctmr); list_add_tail(&ctmr->elist, firing); } @@ -1161,7 +1163,49 @@ static void handle_posix_cpu_timers(struct task_struct *tsk); #ifdef CONFIG_POSIX_CPU_TIMERS_TASK_WORK static void posix_cpu_timers_work(struct callback_head *work) { + struct posix_cputimers_work *cw = container_of(work, typeof(*cw), work); + + mutex_lock(&cw->mutex); handle_posix_cpu_timers(current); + mutex_unlock(&cw->mutex); +} + +/* + * Invoked from the posix-timer core when a cancel operation failed because + * the timer is marked firing. The caller holds rcu_read_lock(), which + * protects the timer and the task which is expiring it from being freed. + */ +static void posix_cpu_timer_wait_running(struct k_itimer *timr) +{ + struct task_struct *tsk = rcu_dereference(timr->it.cpu.handling); + + /* Has the handling task completed expiry already? */ + if (!tsk) + return; + + /* Ensure that the task cannot go away */ + get_task_struct(tsk); + /* Now drop the RCU protection so the mutex can be locked */ + rcu_read_unlock(); + /* Wait on the expiry mutex */ + mutex_lock(&tsk->posix_cputimers_work.mutex); + /* Release it immediately again. */ + mutex_unlock(&tsk->posix_cputimers_work.mutex); + /* Drop the task reference. */ + put_task_struct(tsk); + /* Relock RCU so the callsite is balanced */ + rcu_read_lock(); +} + +static void posix_cpu_timer_wait_running_nsleep(struct k_itimer *timr) +{ + /* Ensure that timr->it.cpu.handling task cannot go away */ + rcu_read_lock(); + spin_unlock_irq(&timr->it_lock); + posix_cpu_timer_wait_running(timr); + rcu_read_unlock(); + /* @timr is on stack and is valid */ + spin_lock_irq(&timr->it_lock); } /* @@ -1177,6 +1221,7 @@ void clear_posix_cputimers_work(struct task_struct *p) sizeof(p->posix_cputimers_work.work)); init_task_work(&p->posix_cputimers_work.work, posix_cpu_timers_work); + mutex_init(&p->posix_cputimers_work.mutex); p->posix_cputimers_work.scheduled = false; } @@ -1255,6 +1300,18 @@ static inline void __run_posix_cpu_timers(struct task_struct *tsk) lockdep_posixtimer_exit(); } +static void posix_cpu_timer_wait_running(struct k_itimer *timr) +{ + cpu_relax(); +} + +static void posix_cpu_timer_wait_running_nsleep(struct k_itimer *timr) +{ + spin_unlock_irq(&timr->it_lock); + cpu_relax(); + spin_lock_irq(&timr->it_lock); +} + static inline bool posix_cpu_timers_work_scheduled(struct task_struct *tsk) { return false; @@ -1363,6 +1420,8 @@ static void handle_posix_cpu_timers(struct task_struct *tsk) */ if (likely(cpu_firing >= 0)) cpu_timer_fire(timer); + /* See posix_cpu_timer_wait_running() */ + rcu_assign_pointer(timer->it.cpu.handling, NULL); spin_unlock(&timer->it_lock); } } @@ -1497,23 +1556,16 @@ static int do_cpu_nanosleep(const clockid_t which_clock, int flags, expires = cpu_timer_getexpires(&timer.it.cpu); error = posix_cpu_timer_set(&timer, 0, &zero_it, &it); if (!error) { - /* - * Timer is now unarmed, deletion can not fail. - */ + /* Timer is now unarmed, deletion can not fail. */ posix_cpu_timer_del(&timer); + } else { + while (error == TIMER_RETRY) { + posix_cpu_timer_wait_running_nsleep(&timer); + error = posix_cpu_timer_del(&timer); + } } - spin_unlock_irq(&timer.it_lock); - while (error == TIMER_RETRY) { - /* - * We need to handle case when timer was or is in the - * middle of firing. In other cases we already freed - * resources. - */ - spin_lock_irq(&timer.it_lock); - error = posix_cpu_timer_del(&timer); - spin_unlock_irq(&timer.it_lock); - } + spin_unlock_irq(&timer.it_lock); if ((it.it_value.tv_sec | it.it_value.tv_nsec) == 0) { /* @@ -1623,6 +1675,7 @@ const struct k_clock clock_posix_cpu = { .timer_del = posix_cpu_timer_del, .timer_get = posix_cpu_timer_get, .timer_rearm = posix_cpu_timer_rearm, + .timer_wait_running = posix_cpu_timer_wait_running, }; const struct k_clock clock_process = { diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c index 0c8a87a11b39..808a247205a9 100644 --- a/kernel/time/posix-timers.c +++ b/kernel/time/posix-timers.c @@ -846,6 +846,10 @@ static struct k_itimer *timer_wait_running(struct k_itimer *timer, rcu_read_lock(); unlock_timer(timer, *flags); + /* + * kc->timer_wait_running() might drop RCU lock. So @timer + * cannot be touched anymore after the function returns! + */ if (!WARN_ON_ONCE(!kc->timer_wait_running)) kc->timer_wait_running(timer); |