linux/include/asm-generic/qrwlock.h
Waiman Long d8d0da4eee locking/arch: Move qrwlock.h include after qspinlock.h
include/asm-generic/qrwlock.h was trying to get arch_spin_is_locked via
asm-generic/qspinlock.h.  However, this does not work because architectures
might be using queued rwlocks but not queued spinlocks (csky), or because they
might be defining their own queued_* macros before including asm/qspinlock.h.

To fix this, ensure that asm/spinlock.h always includes qrwlock.h after
defining arch_spin_is_locked (either directly for csky, or via
asm/qspinlock.h for other architectures).  The only inclusion elsewhere
is in kernel/locking/qrwlock.c.  That one is really unnecessary because
the file is only compiled in SMP configurations (config QUEUED_RWLOCKS
depends on SMP) and in that case linux/spinlock.h already includes
asm/qrwlock.h if needed, via asm/spinlock.h.

Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Waiman Long <longman@redhat.com>
Fixes: 26128cb6c7 ("locking/rwlocks: Add contention detection for rwlocks")
Tested-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Ben Gardon <bgardon@google.com>
[Add arch/sparc and kernel/locking parts per discussion with Waiman. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2021-02-11 07:59:54 -05:00

144 lines
3.8 KiB
C

/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
* Queue read/write lock
*
* (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P.
*
* Authors: Waiman Long <waiman.long@hp.com>
*/
#ifndef __ASM_GENERIC_QRWLOCK_H
#define __ASM_GENERIC_QRWLOCK_H
#include <linux/atomic.h>
#include <asm/barrier.h>
#include <asm/processor.h>
#include <asm-generic/qrwlock_types.h>
/* Must be included from asm/spinlock.h after defining arch_spin_is_locked. */
/*
* Writer states & reader shift and bias.
*/
#define _QW_WAITING 0x100 /* A writer is waiting */
#define _QW_LOCKED 0x0ff /* A writer holds the lock */
#define _QW_WMASK 0x1ff /* Writer mask */
#define _QR_SHIFT 9 /* Reader count shift */
#define _QR_BIAS (1U << _QR_SHIFT)
/*
* External function declarations
*/
extern void queued_read_lock_slowpath(struct qrwlock *lock);
extern void queued_write_lock_slowpath(struct qrwlock *lock);
/**
* queued_read_trylock - try to acquire read lock of a queue rwlock
* @lock : Pointer to queue rwlock structure
* Return: 1 if lock acquired, 0 if failed
*/
static inline int queued_read_trylock(struct qrwlock *lock)
{
int cnts;
cnts = atomic_read(&lock->cnts);
if (likely(!(cnts & _QW_WMASK))) {
cnts = (u32)atomic_add_return_acquire(_QR_BIAS, &lock->cnts);
if (likely(!(cnts & _QW_WMASK)))
return 1;
atomic_sub(_QR_BIAS, &lock->cnts);
}
return 0;
}
/**
* queued_write_trylock - try to acquire write lock of a queue rwlock
* @lock : Pointer to queue rwlock structure
* Return: 1 if lock acquired, 0 if failed
*/
static inline int queued_write_trylock(struct qrwlock *lock)
{
int cnts;
cnts = atomic_read(&lock->cnts);
if (unlikely(cnts))
return 0;
return likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts,
_QW_LOCKED));
}
/**
* queued_read_lock - acquire read lock of a queue rwlock
* @lock: Pointer to queue rwlock structure
*/
static inline void queued_read_lock(struct qrwlock *lock)
{
int cnts;
cnts = atomic_add_return_acquire(_QR_BIAS, &lock->cnts);
if (likely(!(cnts & _QW_WMASK)))
return;
/* The slowpath will decrement the reader count, if necessary. */
queued_read_lock_slowpath(lock);
}
/**
* queued_write_lock - acquire write lock of a queue rwlock
* @lock : Pointer to queue rwlock structure
*/
static inline void queued_write_lock(struct qrwlock *lock)
{
int cnts = 0;
/* Optimize for the unfair lock case where the fair flag is 0. */
if (likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED)))
return;
queued_write_lock_slowpath(lock);
}
/**
* queued_read_unlock - release read lock of a queue rwlock
* @lock : Pointer to queue rwlock structure
*/
static inline void queued_read_unlock(struct qrwlock *lock)
{
/*
* Atomically decrement the reader count
*/
(void)atomic_sub_return_release(_QR_BIAS, &lock->cnts);
}
/**
* queued_write_unlock - release write lock of a queue rwlock
* @lock : Pointer to queue rwlock structure
*/
static inline void queued_write_unlock(struct qrwlock *lock)
{
smp_store_release(&lock->wlocked, 0);
}
/**
* queued_rwlock_is_contended - check if the lock is contended
* @lock : Pointer to queue rwlock structure
* Return: 1 if lock contended, 0 otherwise
*/
static inline int queued_rwlock_is_contended(struct qrwlock *lock)
{
return arch_spin_is_locked(&lock->wait_lock);
}
/*
* Remapping rwlock architecture specific functions to the corresponding
* queue rwlock functions.
*/
#define arch_read_lock(l) queued_read_lock(l)
#define arch_write_lock(l) queued_write_lock(l)
#define arch_read_trylock(l) queued_read_trylock(l)
#define arch_write_trylock(l) queued_write_trylock(l)
#define arch_read_unlock(l) queued_read_unlock(l)
#define arch_write_unlock(l) queued_write_unlock(l)
#define arch_rwlock_is_contended(l) queued_rwlock_is_contended(l)
#endif /* __ASM_GENERIC_QRWLOCK_H */