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![Marco Elver](/assets/img/avatar_default.png)
Implement simple accessors to probe percpu-rwsem's locked state: percpu_is_write_locked(), percpu_is_read_locked(). Signed-off-by: Marco Elver <elver@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Dmitry Vyukov <dvyukov@google.com> Acked-by: Ian Rogers <irogers@google.com> Link: https://lore.kernel.org/r/20220829124719.675715-11-elver@google.com
159 lines
4.3 KiB
C
159 lines
4.3 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_PERCPU_RWSEM_H
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#define _LINUX_PERCPU_RWSEM_H
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#include <linux/atomic.h>
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#include <linux/percpu.h>
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#include <linux/rcuwait.h>
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#include <linux/wait.h>
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#include <linux/rcu_sync.h>
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#include <linux/lockdep.h>
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struct percpu_rw_semaphore {
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struct rcu_sync rss;
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unsigned int __percpu *read_count;
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struct rcuwait writer;
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wait_queue_head_t waiters;
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atomic_t block;
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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struct lockdep_map dep_map;
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#endif
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};
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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#define __PERCPU_RWSEM_DEP_MAP_INIT(lockname) .dep_map = { .name = #lockname },
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#else
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#define __PERCPU_RWSEM_DEP_MAP_INIT(lockname)
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#endif
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#define __DEFINE_PERCPU_RWSEM(name, is_static) \
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static DEFINE_PER_CPU(unsigned int, __percpu_rwsem_rc_##name); \
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is_static struct percpu_rw_semaphore name = { \
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.rss = __RCU_SYNC_INITIALIZER(name.rss), \
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.read_count = &__percpu_rwsem_rc_##name, \
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.writer = __RCUWAIT_INITIALIZER(name.writer), \
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.waiters = __WAIT_QUEUE_HEAD_INITIALIZER(name.waiters), \
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.block = ATOMIC_INIT(0), \
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__PERCPU_RWSEM_DEP_MAP_INIT(name) \
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}
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#define DEFINE_PERCPU_RWSEM(name) \
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__DEFINE_PERCPU_RWSEM(name, /* not static */)
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#define DEFINE_STATIC_PERCPU_RWSEM(name) \
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__DEFINE_PERCPU_RWSEM(name, static)
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extern bool __percpu_down_read(struct percpu_rw_semaphore *, bool);
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static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
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{
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might_sleep();
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rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
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preempt_disable();
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/*
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* We are in an RCU-sched read-side critical section, so the writer
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* cannot both change sem->state from readers_fast and start checking
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* counters while we are here. So if we see !sem->state, we know that
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* the writer won't be checking until we're past the preempt_enable()
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* and that once the synchronize_rcu() is done, the writer will see
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* anything we did within this RCU-sched read-size critical section.
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*/
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if (likely(rcu_sync_is_idle(&sem->rss)))
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this_cpu_inc(*sem->read_count);
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else
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__percpu_down_read(sem, false); /* Unconditional memory barrier */
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/*
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* The preempt_enable() prevents the compiler from
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* bleeding the critical section out.
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*/
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preempt_enable();
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}
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static inline bool percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
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{
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bool ret = true;
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preempt_disable();
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/*
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* Same as in percpu_down_read().
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*/
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if (likely(rcu_sync_is_idle(&sem->rss)))
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this_cpu_inc(*sem->read_count);
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else
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ret = __percpu_down_read(sem, true); /* Unconditional memory barrier */
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preempt_enable();
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/*
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* The barrier() from preempt_enable() prevents the compiler from
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* bleeding the critical section out.
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*/
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if (ret)
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rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
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return ret;
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}
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static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
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{
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rwsem_release(&sem->dep_map, _RET_IP_);
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preempt_disable();
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/*
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* Same as in percpu_down_read().
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*/
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if (likely(rcu_sync_is_idle(&sem->rss))) {
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this_cpu_dec(*sem->read_count);
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} else {
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/*
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* slowpath; reader will only ever wake a single blocked
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* writer.
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*/
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smp_mb(); /* B matches C */
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/*
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* In other words, if they see our decrement (presumably to
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* aggregate zero, as that is the only time it matters) they
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* will also see our critical section.
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*/
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this_cpu_dec(*sem->read_count);
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rcuwait_wake_up(&sem->writer);
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}
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preempt_enable();
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}
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extern bool percpu_is_read_locked(struct percpu_rw_semaphore *);
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extern void percpu_down_write(struct percpu_rw_semaphore *);
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extern void percpu_up_write(struct percpu_rw_semaphore *);
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static inline bool percpu_is_write_locked(struct percpu_rw_semaphore *sem)
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{
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return atomic_read(&sem->block);
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}
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extern int __percpu_init_rwsem(struct percpu_rw_semaphore *,
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const char *, struct lock_class_key *);
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extern void percpu_free_rwsem(struct percpu_rw_semaphore *);
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#define percpu_init_rwsem(sem) \
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({ \
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static struct lock_class_key rwsem_key; \
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__percpu_init_rwsem(sem, #sem, &rwsem_key); \
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})
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#define percpu_rwsem_is_held(sem) lockdep_is_held(sem)
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#define percpu_rwsem_assert_held(sem) lockdep_assert_held(sem)
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static inline void percpu_rwsem_release(struct percpu_rw_semaphore *sem,
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bool read, unsigned long ip)
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{
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lock_release(&sem->dep_map, ip);
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}
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static inline void percpu_rwsem_acquire(struct percpu_rw_semaphore *sem,
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bool read, unsigned long ip)
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{
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lock_acquire(&sem->dep_map, 0, 1, read, 1, NULL, ip);
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}
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#endif
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