include/linux/rcupdate_trace.h

/* SPDX-License-Identifier: GPL-2.0+ */
/*
 * Read-Copy Update mechanism for mutual exclusion, adapted for tracing.
 *
 * Copyright (C) 2020 Paul E. McKenney.
 */

#ifndef __LINUX_RCUPDATE_TRACE_H
#define __LINUX_RCUPDATE_TRACE_H

#include <linux/sched.h>
#include <linux/rcupdate.h>

extern struct lockdep_map rcu_trace_lock_map;

#ifdef CONFIG_DEBUG_LOCK_ALLOC

static inline int rcu_read_lock_trace_held(void)
{
	return lock_is_held(&rcu_trace_lock_map);
}

#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

static inline int rcu_read_lock_trace_held(void)
{
	return 1;
}

#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */

#ifdef CONFIG_TASKS_TRACE_RCU

void rcu_read_unlock_trace_special(struct task_struct *t);

/**
 * rcu_read_lock_trace - mark beginning of RCU-trace read-side critical section
 *
 * When synchronize_rcu_tasks_trace() is invoked by one task, then that
 * task is guaranteed to block until all other tasks exit their read-side
 * critical sections.  Similarly, if call_rcu_trace() is invoked on one
 * task while other tasks are within RCU read-side critical sections,
 * invocation of the corresponding RCU callback is deferred until after
 * the all the other tasks exit their critical sections.
 *
 * For more details, please see the documentation for rcu_read_lock().
 */
static inline void rcu_read_lock_trace(void)
{
	struct task_struct *t = current;

	WRITE_ONCE(t->trc_reader_nesting, READ_ONCE(t->trc_reader_nesting) + 1);
	barrier();
	if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) &&
	    t->trc_reader_special.b.need_mb)
		smp_mb(); // Pairs with update-side barriers
	rcu_lock_acquire(&rcu_trace_lock_map);
}

/**
 * rcu_read_unlock_trace - mark end of RCU-trace read-side critical section
 *
 * Pairs with a preceding call to rcu_read_lock_trace(), and nesting is
 * allowed.  Invoking a rcu_read_unlock_trace() when there is no matching
 * rcu_read_lock_trace() is verboten, and will result in lockdep complaints.
 *
 * For more details, please see the documentation for rcu_read_unlock().
 */
static inline void rcu_read_unlock_trace(void)
{
	int nesting;
	struct task_struct *t = current;

	rcu_lock_release(&rcu_trace_lock_map);
	nesting = READ_ONCE(t->trc_reader_nesting) - 1;
	barrier(); // Critical section before disabling.
	// Disable IPI-based setting of .need_qs.
	WRITE_ONCE(t->trc_reader_nesting, INT_MIN + nesting);
	if (likely(!READ_ONCE(t->trc_reader_special.s)) || nesting) {
		WRITE_ONCE(t->trc_reader_nesting, nesting);
		return;  // We assume shallow reader nesting.
	}
	WARN_ON_ONCE(nesting != 0);
	rcu_read_unlock_trace_special(t);
}

void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func);
void synchronize_rcu_tasks_trace(void);
void rcu_barrier_tasks_trace(void);
struct task_struct *get_rcu_tasks_trace_gp_kthread(void);
#else
/*
 * The BPF JIT forms these addresses even when it doesn't call these
 * functions, so provide definitions that result in runtime errors.
 */
static inline void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func) { BUG(); }
static inline void rcu_read_lock_trace(void) { BUG(); }
static inline void rcu_read_unlock_trace(void) { BUG(); }
#endif /* #ifdef CONFIG_TASKS_TRACE_RCU */

#endif /* __LINUX_RCUPDATE_TRACE_H */