rcu: Warn when srcu_read_lock() is used in an extended quiescent state

#define _LINUX_SRCU_H

#include <linux/mutex.h>

#include <linux/rcupdate.h>

struct srcu_struct_array {

	int c[2];

	__init_srcu_struct((sp), #sp, &__srcu_key); \

})

# define srcu_read_acquire(sp) \

		lock_acquire(&(sp)->dep_map, 0, 0, 2, 1, NULL, _THIS_IP_)

# define srcu_read_release(sp) \

		lock_release(&(sp)->dep_map, 1, _THIS_IP_)

#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

int init_srcu_struct(struct srcu_struct *sp);

# define srcu_read_acquire(sp)  do { } while (0)

# define srcu_read_release(sp)  do { } while (0)

#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */

void cleanup_srcu_struct(struct srcu_struct *sp);

 * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,

 * this assumes we are in an SRCU read-side critical section unless it can

 * prove otherwise.

 *

 * Note that if the CPU is in the idle loop from an RCU point of view

 * (ie: that we are in the section between rcu_idle_enter() and

 * rcu_idle_exit()) then srcu_read_lock_held() returns false even if

 * the CPU did an srcu_read_lock().  The reason for this is that RCU

 * ignores CPUs that are in such a section, considering these as in

 * extended quiescent state, so such a CPU is effectively never in an

 * RCU read-side critical section regardless of what RCU primitives it

 * invokes.  This state of affairs is required --- we need to keep an

 * RCU-free window in idle where the CPU may possibly enter into low

 * power mode. This way we can notice an extended quiescent state to

 * other CPUs that started a grace period. Otherwise we would delay any

 * grace period as long as we run in the idle task.

 */

static inline int srcu_read_lock_held(struct srcu_struct *sp)

{

	if (debug_locks)

		return lock_is_held(&sp->dep_map);

	if (rcu_is_cpu_idle())

		return 0;

	if (!debug_locks)

		return 1;

	return lock_is_held(&sp->dep_map);

}

#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

{

	int retval = __srcu_read_lock(sp);

	srcu_read_acquire(sp);

	rcu_lock_acquire(&(sp)->dep_map);

	return retval;

}

static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)

	__releases(sp)

{

	srcu_read_release(sp);

	rcu_lock_release(&(sp)->dep_map);

	__srcu_read_unlock(sp, idx);

}