path: root/include/spl/sys/rwlock.h

/*
 *  Copyright (C) 2007-2010 Lawrence Livermore National Security, LLC.
 *  Copyright (C) 2007 The Regents of the University of California.
 *  Produced at Lawrence Livermore National Laboratory (cf, DISCLAIMER).
 *  Written by Brian Behlendorf <behlendorf1@llnl.gov>.
 *  UCRL-CODE-235197
 *
 *  This file is part of the SPL, Solaris Porting Layer.
 *  For details, see <http://zfsonlinux.org/>.
 *
 *  The SPL is free software; you can redistribute it and/or modify it
 *  under the terms of the GNU General Public License as published by the
 *  Free Software Foundation; either version 2 of the License, or (at your
 *  option) any later version.
 *
 *  The SPL is distributed in the hope that it will be useful, but WITHOUT
 *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 *  for more details.
 *
 *  You should have received a copy of the GNU General Public License along
 *  with the SPL.  If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef _SPL_RWLOCK_H
#define	_SPL_RWLOCK_H

#include <sys/types.h>
#include <linux/rwsem.h>
#include <linux/sched.h>

/* Linux kernel compatibility */
#if defined(CONFIG_PREEMPT_RT_FULL)
#define	SPL_RWSEM_SINGLE_READER_VALUE	(1)
#define	SPL_RWSEM_SINGLE_WRITER_VALUE	(0)
#elif defined(CONFIG_RWSEM_GENERIC_SPINLOCK)
#define	SPL_RWSEM_SINGLE_READER_VALUE	(1)
#define	SPL_RWSEM_SINGLE_WRITER_VALUE	(-1)
#elif defined(RWSEM_ACTIVE_MASK)
#define	SPL_RWSEM_SINGLE_READER_VALUE	(RWSEM_ACTIVE_READ_BIAS)
#define	SPL_RWSEM_SINGLE_WRITER_VALUE	(RWSEM_ACTIVE_WRITE_BIAS)
#endif

/* Linux 3.16 changed activity to count for rwsem-spinlock */
#if defined(CONFIG_PREEMPT_RT_FULL)
#define	RWSEM_COUNT(sem)	sem->read_depth
#elif defined(HAVE_RWSEM_ACTIVITY)
#define	RWSEM_COUNT(sem)	sem->activity
/* Linux 4.8 changed count to an atomic_long_t for !rwsem-spinlock */
#elif defined(HAVE_RWSEM_ATOMIC_LONG_COUNT)
#define	RWSEM_COUNT(sem)	atomic_long_read(&(sem)->count)
#else
#define	RWSEM_COUNT(sem)	sem->count
#endif

#if defined(RWSEM_SPINLOCK_IS_RAW)
#define	spl_rwsem_lock_irqsave(lk, fl)		raw_spin_lock_irqsave(lk, fl)
#define	spl_rwsem_unlock_irqrestore(lk, fl)	\
    raw_spin_unlock_irqrestore(lk, fl)
#define	spl_rwsem_trylock_irqsave(lk, fl)	raw_spin_trylock_irqsave(lk, fl)
#else
#define	spl_rwsem_lock_irqsave(lk, fl)		spin_lock_irqsave(lk, fl)
#define	spl_rwsem_unlock_irqrestore(lk, fl)	spin_unlock_irqrestore(lk, fl)
#define	spl_rwsem_trylock_irqsave(lk, fl)	spin_trylock_irqsave(lk, fl)
#endif /* RWSEM_SPINLOCK_IS_RAW */

#define	spl_rwsem_is_locked(rwsem)		rwsem_is_locked(rwsem)

typedef enum {
	RW_DRIVER	= 2,
	RW_DEFAULT	= 4,
	RW_NOLOCKDEP	= 5
} krw_type_t;

typedef enum {
	RW_NONE		= 0,
	RW_WRITER	= 1,
	RW_READER	= 2
} krw_t;

/*
 * If CONFIG_RWSEM_SPIN_ON_OWNER is defined, rw_semaphore will have an owner
 * field, so we don't need our own.
 */
typedef struct {
	struct rw_semaphore rw_rwlock;
#ifndef CONFIG_RWSEM_SPIN_ON_OWNER
	kthread_t *rw_owner;
#endif
#ifdef CONFIG_LOCKDEP
	krw_type_t	rw_type;
#endif /* CONFIG_LOCKDEP */
} krwlock_t;

#define	SEM(rwp)	(&(rwp)->rw_rwlock)

static inline void
spl_rw_set_owner(krwlock_t *rwp)
{
/*
 * If CONFIG_RWSEM_SPIN_ON_OWNER is defined, down_write, up_write,
 * downgrade_write and __init_rwsem will set/clear owner for us.
 */
#ifndef CONFIG_RWSEM_SPIN_ON_OWNER
	rwp->rw_owner = current;
#endif
}

static inline void
spl_rw_clear_owner(krwlock_t *rwp)
{
#ifndef CONFIG_RWSEM_SPIN_ON_OWNER
	rwp->rw_owner = NULL;
#endif
}

static inline kthread_t *
rw_owner(krwlock_t *rwp)
{
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
	return (SEM(rwp)->owner);
#else
	return (rwp->rw_owner);
#endif
}

#ifdef CONFIG_LOCKDEP
static inline void
spl_rw_set_type(krwlock_t *rwp, krw_type_t type)
{
	rwp->rw_type = type;
}
static inline void
spl_rw_lockdep_off_maybe(krwlock_t *rwp)		\
{							\
	if (rwp && rwp->rw_type == RW_NOLOCKDEP)	\
		lockdep_off();				\
}
static inline void
spl_rw_lockdep_on_maybe(krwlock_t *rwp)			\
{							\
	if (rwp && rwp->rw_type == RW_NOLOCKDEP)	\
		lockdep_on();				\
}
#else  /* CONFIG_LOCKDEP */
#define	spl_rw_set_type(rwp, type)
#define	spl_rw_lockdep_off_maybe(rwp)
#define	spl_rw_lockdep_on_maybe(rwp)
#endif /* CONFIG_LOCKDEP */


static inline int
RW_WRITE_HELD(krwlock_t *rwp)
{
	return (rw_owner(rwp) == current);
}

static inline int
RW_LOCK_HELD(krwlock_t *rwp)
{
	return (spl_rwsem_is_locked(SEM(rwp)));
}

static inline int
RW_READ_HELD(krwlock_t *rwp)
{
	if (!RW_LOCK_HELD(rwp))
		return (0);

	/*
	 * rw_semaphore cheat sheet:
	 *
	 * < 3.16:
	 * There's no rw_semaphore.owner, so use rwp.owner instead.
	 * If rwp.owner == NULL then it's a reader
	 *
	 * 3.16 - 4.7:
	 * rw_semaphore.owner added (https://lwn.net/Articles/596656/)
	 * and CONFIG_RWSEM_SPIN_ON_OWNER introduced.
	 * If rw_semaphore.owner == NULL then it's a reader
	 *
	 * 4.8 - 4.16.16:
	 * RWSEM_READER_OWNED added as an internal #define.
	 * (https://lore.kernel.org/patchwork/patch/678590/)
	 * If rw_semaphore.owner == 1 then it's a reader
	 *
	 * 4.16.17 - 4.19:
	 * RWSEM_OWNER_UNKNOWN introduced as ((struct task_struct *)-1L)
	 * (https://do-db2.lkml.org/lkml/2018/5/15/985)
	 * If rw_semaphore.owner == 1 then it's a reader.
	 *
	 * 4.20+:
	 * RWSEM_OWNER_UNKNOWN changed to ((struct task_struct *)-2L)
	 * (https://lkml.org/lkml/2018/9/6/986)
	 * If rw_semaphore.owner & 1 then it's a reader, and also the reader's
	 * task_struct may be embedded in rw_semaphore->owner.
	 */
#if	defined(CONFIG_RWSEM_SPIN_ON_OWNER) && defined(RWSEM_OWNER_UNKNOWN)
	if (RWSEM_OWNER_UNKNOWN == (struct task_struct *)-2L) {
		/* 4.20+ kernels with CONFIG_RWSEM_SPIN_ON_OWNER */
		return ((unsigned long) SEM(rwp)->owner & 1);
	}
#endif

	/* < 4.20 kernel or !CONFIG_RWSEM_SPIN_ON_OWNER */
	return (rw_owner(rwp) == NULL || (unsigned long) rw_owner(rwp) == 1);
}

/*
 * The following functions must be a #define and not static inline.
 * This ensures that the native linux semaphore functions (down/up)
 * will be correctly located in the users code which is important
 * for the built in kernel lock analysis tools
 */
/* BEGIN CSTYLED */
#define	rw_init(rwp, name, type, arg)					\
({									\
	static struct lock_class_key __key;				\
	ASSERT(type == RW_DEFAULT || type == RW_NOLOCKDEP);		\
									\
	__init_rwsem(SEM(rwp), #rwp, &__key);				\
	spl_rw_clear_owner(rwp);					\
	spl_rw_set_type(rwp, type);					\
})

/*
 * The Linux rwsem implementation does not require a matching destroy.
 */
#define	rw_destroy(rwp)		((void) 0)

#define	rw_tryenter(rwp, rw)						\
({									\
	int _rc_ = 0;							\
									\
	spl_rw_lockdep_off_maybe(rwp);					\
	switch (rw) {							\
	case RW_READER:							\
		_rc_ = down_read_trylock(SEM(rwp));			\
		break;							\
	case RW_WRITER:							\
		if ((_rc_ = down_write_trylock(SEM(rwp))))		\
			spl_rw_set_owner(rwp);				\
		break;							\
	default:							\
		VERIFY(0);						\
	}								\
	spl_rw_lockdep_on_maybe(rwp);					\
	_rc_;								\
})

#define	rw_enter(rwp, rw)						\
({									\
	spl_rw_lockdep_off_maybe(rwp);					\
	switch (rw) {							\
	case RW_READER:							\
		down_read(SEM(rwp));					\
		break;							\
	case RW_WRITER:							\
		down_write(SEM(rwp));					\
		spl_rw_set_owner(rwp);					\
		break;							\
	default:							\
		VERIFY(0);						\
	}								\
	spl_rw_lockdep_on_maybe(rwp);					\
})

#define	rw_exit(rwp)							\
({									\
	spl_rw_lockdep_off_maybe(rwp);					\
	if (RW_WRITE_HELD(rwp)) {					\
		spl_rw_clear_owner(rwp);				\
		up_write(SEM(rwp));					\
	} else {							\
		ASSERT(RW_READ_HELD(rwp));				\
		up_read(SEM(rwp));					\
	}								\
	spl_rw_lockdep_on_maybe(rwp);					\
})

#define	rw_downgrade(rwp)						\
({									\
	spl_rw_lockdep_off_maybe(rwp);					\
	spl_rw_clear_owner(rwp);					\
	downgrade_write(SEM(rwp));					\
	spl_rw_lockdep_on_maybe(rwp);					\
})

#define	rw_tryupgrade(rwp)						\
({									\
	int _rc_ = 0;							\
									\
	if (RW_WRITE_HELD(rwp)) {					\
		_rc_ = 1;						\
	} else {							\
		spl_rw_lockdep_off_maybe(rwp);				\
		if ((_rc_ = rwsem_tryupgrade(SEM(rwp))))		\
			spl_rw_set_owner(rwp);				\
		spl_rw_lockdep_on_maybe(rwp);				\
	}								\
	_rc_;								\
})
/* END CSTYLED */

int spl_rw_init(void);
void spl_rw_fini(void);
int rwsem_tryupgrade(struct rw_semaphore *rwsem);

#endif /* _SPL_RWLOCK_H */