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optee中spinlock的實現原理詳解


說明: 在默認的情況下，本文講述的是armv8 aarch64體系，optee 3.12.0代碼

在optee中，mutex的實現方式是依賴REE測的completion完成量的，具體流程圖如下所示：

相關代碼：

static void __mutex_lock(struct mutex *m, const char *fname, int lineno) {assert_have_no_spinlock();assert(thread_get_id_may_fail() != THREAD_ID_INVALID);assert(thread_is_in_normal_mode());mutex_lock_check(m);while (true) {uint32_t old_itr_status;bool can_lock;struct wait_queue_elem wqe;/** If the mutex is locked we need to initialize the wqe* before releasing the spinlock to guarantee that we don't* miss the wakeup from mutex_unlock().** If the mutex is unlocked we don't need to use the wqe at* all.*/old_itr_status = cpu_spin_lock_xsave(&m->spin_lock);can_lock = !m->state;if (!can_lock) {wq_wait_init(&m->wq, &wqe, false /* wait_read */);} else {m->state = -1; /* write locked */}cpu_spin_unlock_xrestore(&m->spin_lock, old_itr_status);if (!can_lock) {/** Someone else is holding the lock, wait in normal* world for the lock to become available.*/wq_wait_final(&m->wq, &wqe, m, fname, lineno);} elsereturn;} } static void __mutex_unlock(struct mutex *m, const char *fname, int lineno) {uint32_t old_itr_status;assert_have_no_spinlock();assert(thread_get_id_may_fail() != THREAD_ID_INVALID);mutex_unlock_check(m);old_itr_status = cpu_spin_lock_xsave(&m->spin_lock);if (!m->state)panic();m->state = 0;cpu_spin_unlock_xrestore(&m->spin_lock, old_itr_status);wq_wake_next(&m->wq, m, fname, lineno); }

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