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kernel: sem: handle resets with outstanding waiting threads

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Previously, a k_sem_reset with any outstanding waiting threads would
result in the semaphore in an inconsistent state, with more threads
waiting in the wait_q than the count would indicate.

Explicitly -EAGAIN any waiting threads upon k_sem_reset, to
ensure safety here.

Signed-off-by: James Harris <james.harris@intel.com>
This commit is contained in:
James Harris 2021-03-04 15:47:27 -08:00 • committed by Anas Nashif
commit 53b8179371
2 changed files with 24 additions and 10 deletions
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15
include/kernel.h
View file

@ -2769,7 +2769,8 @@ __syscall int k_sem_init(struct k_sem *sem, unsigned int initial_count,
*
* @retval 0 Semaphore taken.
* @retval -EBUSY Returned without waiting.
* @retval -EAGAIN Waiting period timed out.
* @retval -EAGAIN Waiting period timed out,
* or the semaphore was reset during the waiting period.
*/
__syscall int k_sem_take(struct k_sem *sem, k_timeout_t timeout);
@ -2788,9 +2789,11 @@ __syscall int k_sem_take(struct k_sem *sem, k_timeout_t timeout);
__syscall void k_sem_give(struct k_sem *sem);
/**
* @brief Reset a semaphore's count to zero.
* @brief Resets a semaphore's count to zero.
*
* This routine sets the count of @a sem to zero.
* Any outstanding semaphore takes will be aborted
* with -EAGAIN.
*
* @param sem Address of the semaphore.
*
@ -2798,14 +2801,6 @@ __syscall void k_sem_give(struct k_sem *sem);
*/
__syscall void k_sem_reset(struct k_sem *sem);
/**
* @internal
*/
static inline void z_impl_k_sem_reset(struct k_sem *sem)
{
sem->count = 0U;
}
/**
* @brief Get a semaphore's count.
*

19
kernel/sem.c
View file

@ -163,6 +163,25 @@ out:
return ret;
}
void z_impl_k_sem_reset(struct k_sem *sem)
{
struct k_thread *thread;
k_spinlock_key_t key = k_spin_lock(&lock);
while (true) {
thread = z_unpend_first_thread(&sem->wait_q);
if (thread == NULL) {
break;
}
arch_thread_return_value_set(thread, -EAGAIN);
z_ready_thread(thread);
}
sem->count = 0;
handle_poll_events(sem);
z_reschedule(&lock, key);
}
#ifdef CONFIG_USERSPACE
static inline int z_vrfy_k_sem_take(struct k_sem *sem, k_timeout_t timeout)
{