/*
* Copyright (c) 2018, NVIDIA CORPORATION. All rights reserved.
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
* DEALINGS IN THE SOFTWARE.
*/
#include <nvgpu/bug.h>
#include <nvgpu/rwsem.h>
#include <nvgpu/timers.h>
#include <nvgpu/posix/rwsem.h>
void nvgpu_rwsem_init(struct nvgpu_rwsem *rwsem)
{
memset(rwsem, 0, sizeof(*rwsem));
nvgpu_spinlock_init(&rwsem->lock);
}
/*
* Acquire.
*/
void nvgpu_rwsem_down_read(struct nvgpu_rwsem *rwsem)
{
while (true) {
nvgpu_spinlock_acquire(&rwsem->lock);
/*
* If there's a writer try again.
*/
if (rwsem->writers < 0) {
nvgpu_spinlock_release(&rwsem->lock);
nvgpu_msleep(10);
continue;
}
/*
* Otherwise decrement the read counter and return.
*/
rwsem->readers -= 1;
nvgpu_spinlock_release(&rwsem->lock);
return;
}
}
/*
* Release.
*/
void nvgpu_rwsem_up_read(struct nvgpu_rwsem *rwsem)
{
nvgpu_spinlock_acquire(&rwsem->lock);
rwsem->readers += 1;
/*
* Can't be any writers if there was a reader. Also can't be
* a positive number of readers. The increments are always
* downward so if we have a positive number then there is a
* balancing bug.
*/
BUG_ON(rwsem->writers < 0);
BUG_ON(rwsem->readers > 0);
nvgpu_spinlock_release(&rwsem->lock);
}
void nvgpu_rwsem_down_write(struct nvgpu_rwsem *rwsem)
{
while (true) {
nvgpu_spinlock_acquire(&rwsem->lock);
/*
* If there's a reader or a writer try again. Note: in this very
* simple implementation it's possible for readers to
* indefinitely starve writers.
*/
if (rwsem->writers < 0 || rwsem->readers < 0) {
nvgpu_spinlock_release(&rwsem->lock);
nvgpu_msleep(10);
continue;
}
rwsem->writers -= 1;
nvgpu_spinlock_release(&rwsem->lock);
return;
}
}
void nvgpu_rwsem_up_write(struct nvgpu_rwsem *rwsem)
{
nvgpu_spinlock_acquire(&rwsem->lock);
rwsem->writers += 1;
/*
* Writers can't be positive: that would be an unbalanced free. Readers
* must be zero - otherwise this writer should never have had access!
*/
BUG_ON(rwsem->writers > 0);
BUG_ON(rwsem->readers != 0);
nvgpu_spinlock_release(&rwsem->lock);
}
