Contributors: 16
| Author |
Tokens |
Token Proportion |
Commits |
Commit Proportion |
| Peter Zijlstra |
450 |
52.51% |
7 |
22.58% |
| Oleg Nesterov |
197 |
22.99% |
6 |
19.35% |
| Mikulas Patocka |
67 |
7.82% |
1 |
3.23% |
| Ingo Molnar |
46 |
5.37% |
4 |
12.90% |
| Namhyung Kim |
32 |
3.73% |
1 |
3.23% |
| Paul E. McKenney |
19 |
2.22% |
1 |
3.23% |
| Qian Cai |
14 |
1.63% |
1 |
3.23% |
| Marco Elver |
9 |
1.05% |
1 |
3.23% |
| Daeho Jeong |
7 |
0.82% |
1 |
3.23% |
| Davidlohr Bueso A |
5 |
0.58% |
2 |
6.45% |
| Al Viro |
3 |
0.35% |
1 |
3.23% |
| MinChan Kim |
2 |
0.23% |
1 |
3.23% |
| Waiman Long |
2 |
0.23% |
1 |
3.23% |
| Hou Tao |
2 |
0.23% |
1 |
3.23% |
| Thomas Gleixner |
1 |
0.12% |
1 |
3.23% |
| Frédéric Weisbecker |
1 |
0.12% |
1 |
3.23% |
| Total |
857 |
|
31 |
|
// SPDX-License-Identifier: GPL-2.0-only
#include <linux/atomic.h>
#include <linux/percpu.h>
#include <linux/wait.h>
#include <linux/lockdep.h>
#include <linux/percpu-rwsem.h>
#include <linux/rcupdate.h>
#include <linux/sched.h>
#include <linux/sched/task.h>
#include <linux/sched/debug.h>
#include <linux/errno.h>
#include <trace/events/lock.h>
int __percpu_init_rwsem(struct percpu_rw_semaphore *sem,
const char *name, struct lock_class_key *key)
{
sem->read_count = alloc_percpu(int);
if (unlikely(!sem->read_count))
return -ENOMEM;
rcu_sync_init(&sem->rss);
rcuwait_init(&sem->writer);
init_waitqueue_head(&sem->waiters);
atomic_set(&sem->block, 0);
#ifdef CONFIG_DEBUG_LOCK_ALLOC
debug_check_no_locks_freed((void *)sem, sizeof(*sem));
lockdep_init_map(&sem->dep_map, name, key, 0);
#endif
return 0;
}
EXPORT_SYMBOL_GPL(__percpu_init_rwsem);
void percpu_free_rwsem(struct percpu_rw_semaphore *sem)
{
/*
* XXX: temporary kludge. The error path in alloc_super()
* assumes that percpu_free_rwsem() is safe after kzalloc().
*/
if (!sem->read_count)
return;
rcu_sync_dtor(&sem->rss);
free_percpu(sem->read_count);
sem->read_count = NULL; /* catch use after free bugs */
}
EXPORT_SYMBOL_GPL(percpu_free_rwsem);
static bool __percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
{
this_cpu_inc(*sem->read_count);
/*
* Due to having preemption disabled the decrement happens on
* the same CPU as the increment, avoiding the
* increment-on-one-CPU-and-decrement-on-another problem.
*
* If the reader misses the writer's assignment of sem->block, then the
* writer is guaranteed to see the reader's increment.
*
* Conversely, any readers that increment their sem->read_count after
* the writer looks are guaranteed to see the sem->block value, which
* in turn means that they are guaranteed to immediately decrement
* their sem->read_count, so that it doesn't matter that the writer
* missed them.
*/
smp_mb(); /* A matches D */
/*
* If !sem->block the critical section starts here, matched by the
* release in percpu_up_write().
*/
if (likely(!atomic_read_acquire(&sem->block)))
return true;
this_cpu_dec(*sem->read_count);
/* Prod writer to re-evaluate readers_active_check() */
rcuwait_wake_up(&sem->writer);
return false;
}
static inline bool __percpu_down_write_trylock(struct percpu_rw_semaphore *sem)
{
if (atomic_read(&sem->block))
return false;
return atomic_xchg(&sem->block, 1) == 0;
}
static bool __percpu_rwsem_trylock(struct percpu_rw_semaphore *sem, bool reader)
{
if (reader) {
bool ret;
preempt_disable();
ret = __percpu_down_read_trylock(sem);
preempt_enable();
return ret;
}
return __percpu_down_write_trylock(sem);
}
/*
* The return value of wait_queue_entry::func means:
*
* <0 - error, wakeup is terminated and the error is returned
* 0 - no wakeup, a next waiter is tried
* >0 - woken, if EXCLUSIVE, counted towards @nr_exclusive.
*
* We use EXCLUSIVE for both readers and writers to preserve FIFO order,
* and play games with the return value to allow waking multiple readers.
*
* Specifically, we wake readers until we've woken a single writer, or until a
* trylock fails.
*/
static int percpu_rwsem_wake_function(struct wait_queue_entry *wq_entry,
unsigned int mode, int wake_flags,
void *key)
{
bool reader = wq_entry->flags & WQ_FLAG_CUSTOM;
struct percpu_rw_semaphore *sem = key;
struct task_struct *p;
/* concurrent against percpu_down_write(), can get stolen */
if (!__percpu_rwsem_trylock(sem, reader))
return 1;
p = get_task_struct(wq_entry->private);
list_del_init(&wq_entry->entry);
smp_store_release(&wq_entry->private, NULL);
wake_up_process(p);
put_task_struct(p);
return !reader; /* wake (readers until) 1 writer */
}
static void percpu_rwsem_wait(struct percpu_rw_semaphore *sem, bool reader)
{
DEFINE_WAIT_FUNC(wq_entry, percpu_rwsem_wake_function);
bool wait;
spin_lock_irq(&sem->waiters.lock);
/*
* Serialize against the wakeup in percpu_up_write(), if we fail
* the trylock, the wakeup must see us on the list.
*/
wait = !__percpu_rwsem_trylock(sem, reader);
if (wait) {
wq_entry.flags |= WQ_FLAG_EXCLUSIVE | reader * WQ_FLAG_CUSTOM;
__add_wait_queue_entry_tail(&sem->waiters, &wq_entry);
}
spin_unlock_irq(&sem->waiters.lock);
while (wait) {
set_current_state(TASK_UNINTERRUPTIBLE);
if (!smp_load_acquire(&wq_entry.private))
break;
schedule();
}
__set_current_state(TASK_RUNNING);
}
bool __sched __percpu_down_read(struct percpu_rw_semaphore *sem, bool try)
{
if (__percpu_down_read_trylock(sem))
return true;
if (try)
return false;
trace_contention_begin(sem, LCB_F_PERCPU | LCB_F_READ);
preempt_enable();
percpu_rwsem_wait(sem, /* .reader = */ true);
preempt_disable();
trace_contention_end(sem, 0);
return true;
}
EXPORT_SYMBOL_GPL(__percpu_down_read);
#define per_cpu_sum(var) \
({ \
typeof(var) __sum = 0; \
int cpu; \
compiletime_assert_atomic_type(__sum); \
for_each_possible_cpu(cpu) \
__sum += per_cpu(var, cpu); \
__sum; \
})
bool percpu_is_read_locked(struct percpu_rw_semaphore *sem)
{
return per_cpu_sum(*sem->read_count) != 0 && !atomic_read(&sem->block);
}
EXPORT_SYMBOL_GPL(percpu_is_read_locked);
/*
* Return true if the modular sum of the sem->read_count per-CPU variable is
* zero. If this sum is zero, then it is stable due to the fact that if any
* newly arriving readers increment a given counter, they will immediately
* decrement that same counter.
*
* Assumes sem->block is set.
*/
static bool readers_active_check(struct percpu_rw_semaphore *sem)
{
if (per_cpu_sum(*sem->read_count) != 0)
return false;
/*
* If we observed the decrement; ensure we see the entire critical
* section.
*/
smp_mb(); /* C matches B */
return true;
}
void __sched percpu_down_write(struct percpu_rw_semaphore *sem)
{
might_sleep();
rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
trace_contention_begin(sem, LCB_F_PERCPU | LCB_F_WRITE);
/* Notify readers to take the slow path. */
rcu_sync_enter(&sem->rss);
/*
* Try set sem->block; this provides writer-writer exclusion.
* Having sem->block set makes new readers block.
*/
if (!__percpu_down_write_trylock(sem))
percpu_rwsem_wait(sem, /* .reader = */ false);
/* smp_mb() implied by __percpu_down_write_trylock() on success -- D matches A */
/*
* If they don't see our store of sem->block, then we are guaranteed to
* see their sem->read_count increment, and therefore will wait for
* them.
*/
/* Wait for all active readers to complete. */
rcuwait_wait_event(&sem->writer, readers_active_check(sem), TASK_UNINTERRUPTIBLE);
trace_contention_end(sem, 0);
}
EXPORT_SYMBOL_GPL(percpu_down_write);
void percpu_up_write(struct percpu_rw_semaphore *sem)
{
rwsem_release(&sem->dep_map, _RET_IP_);
/*
* Signal the writer is done, no fast path yet.
*
* One reason that we cannot just immediately flip to readers_fast is
* that new readers might fail to see the results of this writer's
* critical section.
*
* Therefore we force it through the slow path which guarantees an
* acquire and thereby guarantees the critical section's consistency.
*/
atomic_set_release(&sem->block, 0);
/*
* Prod any pending reader/writer to make progress.
*/
__wake_up(&sem->waiters, TASK_NORMAL, 1, sem);
/*
* Once this completes (at least one RCU-sched grace period hence) the
* reader fast path will be available again. Safe to use outside the
* exclusive write lock because its counting.
*/
rcu_sync_exit(&sem->rss);
}
EXPORT_SYMBOL_GPL(percpu_up_write);