Messages in this thread Patch in this message | | | Date | Tue, 13 Jul 2021 17:11:08 +0200 | From | Thomas Gleixner <> | Subject | [patch 14/50] locking/rtmutex: Add wake_state to rt_mutex_waiter |
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From: Thomas Gleixner <tglx@linutronix.de>
Regular sleeping locks like mutexes, rtmutexes and rw_semaphores are always entering and leaving a blocking section with task state == TASK_RUNNING.
On a non-RT kernel spinlocks and rwlocks never affect the task state, but on RT kernels these locks are converted to rtmutex based 'sleeping' locks.
So in case of contention the task goes to block which requires to carefully preserve the task state and restore it after acquiring the lock taking regular wakeups for the task into account which happened while the task was blocked. This state preserving is achieved by having a seperate task state for blocking on a RT spin/rwlock and a saved_state field in task_struct along with careful handling of these wakeup scenarios in try_to_wake_up().
To avoid conditionals in the rtmutex code, store the wake state which has to be used for waking a lock waiter in rt_mutex_waiter which allows to handle the regular and RT spin/rwlocks by handing it to wake_up_state().
Signed-off-by: Thomas Gleixner <tglx@linutronix.de> --- kernel/locking/rtmutex.c | 2 +- kernel/locking/rtmutex_common.h | 9 +++++++++ 2 files changed, 10 insertions(+), 1 deletion(-) --- diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index 16e838a1f199..2aaf3bfc1052 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -692,7 +692,7 @@ static int __sched rt_mutex_adjust_prio_chain(struct task_struct *task, * to get the lock. */ if (prerequeue_top_waiter != rt_mutex_top_waiter(lock)) - wake_up_process(rt_mutex_top_waiter(lock)->task); + wake_up_state(waiter->task, waiter->wake_state); raw_spin_unlock_irq(&lock->wait_lock); return 0; } diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h index e7bfe3a8f10e..dbd261911fdc 100644 --- a/kernel/locking/rtmutex_common.h +++ b/kernel/locking/rtmutex_common.h @@ -25,6 +25,7 @@ * @pi_tree_entry: pi node to enqueue into the mutex owner waiters tree * @task: task reference to the blocked task * @lock: Pointer to the rt_mutex on which the waiter blocks + * @wake_state: Wakeup state to use (TASK_NORMAL or TASK_RTLOCK_WAIT) * @prio: Priority of the waiter * @deadline: Deadline of the waiter if applicable */ @@ -33,6 +34,7 @@ struct rt_mutex_waiter { struct rb_node pi_tree_entry; struct task_struct *task; struct rt_mutex *lock; + int wake_state; int prio; u64 deadline; }; @@ -164,9 +166,16 @@ static inline void rt_mutex_init_waiter(struct rt_mutex_waiter *waiter) debug_rt_mutex_init_waiter(waiter); RB_CLEAR_NODE(&waiter->pi_tree_entry); RB_CLEAR_NODE(&waiter->tree_entry); + waiter->wake_state = TASK_NORMAL; waiter->task = NULL; } +static inline void rtlock_init_rtmutex_waiter(struct rt_mutex_waiter *waiter) +{ + rt_mutex_init_waiter(waiter); + waiter->wake_state = TASK_RTLOCK_WAIT; +} + #else /* CONFIG_RT_MUTEXES */ /* Used in rcu/tree_plugin.h */ static inline struct task_struct *rt_mutex_owner(struct rt_mutex *lock)
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