kernel/locking/spinlock_rt.c

Source file repositories/reference/linux-study-clean/kernel/locking/spinlock_rt.c

File Facts

System
Linux kernel
Corpus path
kernel/locking/spinlock_rt.c
Extension
.c
Size
7311 bytes
Lines
288
Domain
Core OS
Bucket
Scheduler, Processes, Timers, Sync, And Syscalls
Inferred role
Core OS: exported/initcall integration point
Status
integration implementation candidate

Why This File Exists

Core operating-system implementation surface: boot, tasks, memory, VFS, syscall-facing interfaces, synchronization, credentials, and isolation.

Dependency Surface

Detected Declarations

Annotated Snippet

// SPDX-License-Identifier: GPL-2.0-only
/*
 * PREEMPT_RT substitution for spin/rw_locks
 *
 * spinlocks and rwlocks on RT are based on rtmutexes, with a few twists to
 * resemble the non RT semantics:
 *
 * - Contrary to plain rtmutexes, spinlocks and rwlocks are state
 *   preserving. The task state is saved before blocking on the underlying
 *   rtmutex, and restored when the lock has been acquired. Regular wakeups
 *   during that time are redirected to the saved state so no wake up is
 *   missed.
 *
 * - Non RT spin/rwlocks disable preemption and eventually interrupts.
 *   Disabling preemption has the side effect of disabling migration and
 *   preventing RCU grace periods.
 *
 *   The RT substitutions explicitly disable migration and take
 *   rcu_read_lock() across the lock held section.
 */
#include <linux/spinlock.h>
#include <linux/export.h>

#define RT_MUTEX_BUILD_SPINLOCKS
#include "rtmutex.c"

/*
 * __might_resched() skips the state check as rtlocks are state
 * preserving. Take RCU nesting into account as spin/read/write_lock() can
 * legitimately nest into an RCU read side critical section.
 */
#define RTLOCK_RESCHED_OFFSETS						\
	(rcu_preempt_depth() << MIGHT_RESCHED_RCU_SHIFT)

#define rtlock_might_resched()						\
	__might_resched(__FILE__, __LINE__, RTLOCK_RESCHED_OFFSETS)

static __always_inline void rtlock_lock(struct rt_mutex_base *rtm)
{
	lockdep_assert(!current->pi_blocked_on);

	if (unlikely(!rt_mutex_cmpxchg_acquire(rtm, NULL, current)))
		rtlock_slowlock(rtm);
}

static __always_inline void __rt_spin_lock(spinlock_t *lock)
{
	rtlock_might_resched();
	rtlock_lock(&lock->lock);
	rcu_read_lock();
	migrate_disable();
}

void __sched rt_spin_lock(spinlock_t *lock) __acquires(RCU)
{
	spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
	__rt_spin_lock(lock);
}
EXPORT_SYMBOL(rt_spin_lock);

#ifdef CONFIG_DEBUG_LOCK_ALLOC
void __sched rt_spin_lock_nested(spinlock_t *lock, int subclass)
{
	spin_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
	__rt_spin_lock(lock);
}
EXPORT_SYMBOL(rt_spin_lock_nested);

void __sched rt_spin_lock_nest_lock(spinlock_t *lock,
				    struct lockdep_map *nest_lock)
{
	spin_acquire_nest(&lock->dep_map, 0, 0, nest_lock, _RET_IP_);
	__rt_spin_lock(lock);
}
EXPORT_SYMBOL(rt_spin_lock_nest_lock);
#endif

void __sched rt_spin_unlock(spinlock_t *lock) __releases(RCU)
{
	spin_release(&lock->dep_map, _RET_IP_);
	migrate_enable();
	rcu_read_unlock();

	if (unlikely(!rt_mutex_cmpxchg_release(&lock->lock, current, NULL)))
		rt_mutex_slowunlock(&lock->lock);
}
EXPORT_SYMBOL(rt_spin_unlock);

/*
 * Wait for the lock to get unlocked: instead of polling for an unlock

Annotation

Implementation Notes