locking/rtmutex: Provide the spin/rwlock core lock function
A simplified version of the rtmutex slowlock function, which neither handles
signals nor timeouts, and is careful about preserving the state of the
blocked task across the lock operation.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.770228446@linutronix.de
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 949781a..951bef0 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1416,3 +1416,63 @@ static __always_inline int __rt_mutex_lock(struct rt_mutex_base *lock,
return rt_mutex_slowlock(lock, state);
}
#endif /* RT_MUTEX_BUILD_MUTEX */
+
+#ifdef RT_MUTEX_BUILD_SPINLOCKS
+/*
+ * Functions required for spin/rw_lock substitution on RT kernels
+ */
+
+/**
+ * rtlock_slowlock_locked - Slow path lock acquisition for RT locks
+ * @lock: The underlying RT mutex
+ */
+static void __sched rtlock_slowlock_locked(struct rt_mutex_base *lock)
+{
+ struct rt_mutex_waiter waiter;
+
+ lockdep_assert_held(&lock->wait_lock);
+
+ if (try_to_take_rt_mutex(lock, current, NULL))
+ return;
+
+ rt_mutex_init_rtlock_waiter(&waiter);
+
+ /* Save current state and set state to TASK_RTLOCK_WAIT */
+ current_save_and_set_rtlock_wait_state();
+
+ task_blocks_on_rt_mutex(lock, &waiter, current, RT_MUTEX_MIN_CHAINWALK);
+
+ for (;;) {
+ /* Try to acquire the lock again */
+ if (try_to_take_rt_mutex(lock, current, &waiter))
+ break;
+
+ raw_spin_unlock_irq(&lock->wait_lock);
+
+ schedule_rtlock();
+
+ raw_spin_lock_irq(&lock->wait_lock);
+ set_current_state(TASK_RTLOCK_WAIT);
+ }
+
+ /* Restore the task state */
+ current_restore_rtlock_saved_state();
+
+ /*
+ * try_to_take_rt_mutex() sets the waiter bit unconditionally.
+ * We might have to fix that up:
+ */
+ fixup_rt_mutex_waiters(lock);
+ debug_rt_mutex_free_waiter(&waiter);
+}
+
+static __always_inline void __sched rtlock_slowlock(struct rt_mutex_base *lock)
+{
+ unsigned long flags;
+
+ raw_spin_lock_irqsave(&lock->wait_lock, flags);
+ rtlock_slowlock_locked(lock);
+ raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
+}
+
+#endif /* RT_MUTEX_BUILD_SPINLOCKS */