open-gpu-kernel-modules/kernel-open/nvidia-uvm/nv-kthread-q.c

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2022-05-09 22:18:59 +02:00
/*
* SPDX-FileCopyrightText: Copyright (c) 2016 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
* SPDX-License-Identifier: MIT
*
* 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 "nv-kthread-q.h"
#include "nv-list-helpers.h"
#include <linux/kthread.h>
#include <linux/interrupt.h>
#include <linux/completion.h>
#include <linux/module.h>
#include <linux/mm.h>
#if defined(NV_LINUX_BUG_H_PRESENT)
#include <linux/bug.h>
#else
#include <asm/bug.h>
#endif
// Today's implementation is a little simpler and more limited than the
// API description allows for in nv-kthread-q.h. Details include:
//
// 1. Each nv_kthread_q instance is a first-in, first-out queue.
//
// 2. Each nv_kthread_q instance is serviced by exactly one kthread.
//
// You can create any number of queues, each of which gets its own
// named kernel thread (kthread). You can then insert arbitrary functions
// into the queue, and those functions will be run in the context of the
// queue's kthread.
#ifndef WARN
// Only *really* old kernels (2.6.9) end up here. Just use a simple printk
// to implement this, because such kernels won't be supported much longer.
#define WARN(condition, format...) ({ \
int __ret_warn_on = !!(condition); \
if (unlikely(__ret_warn_on)) \
printk(KERN_ERR format); \
unlikely(__ret_warn_on); \
})
#endif
#define NVQ_WARN(fmt, ...) \
do { \
if (in_interrupt()) { \
WARN(1, "nv_kthread_q: [in interrupt]: " fmt, \
##__VA_ARGS__); \
} \
else { \
WARN(1, "nv_kthread_q: task: %s: " fmt, \
current->comm, \
##__VA_ARGS__); \
} \
} while (0)
static int _main_loop(void *args)
{
nv_kthread_q_t *q = (nv_kthread_q_t *)args;
nv_kthread_q_item_t *q_item = NULL;
unsigned long flags;
while (1) {
// Normally this thread is never interrupted. However,
// down_interruptible (instead of down) is called here,
// in order to avoid being classified as a potentially
// hung task, by the kernel watchdog.
while (down_interruptible(&q->q_sem))
NVQ_WARN("Interrupted during semaphore wait\n");
if (atomic_read(&q->main_loop_should_exit))
break;
spin_lock_irqsave(&q->q_lock, flags);
// The q_sem semaphore prevents us from getting here unless there is
// at least one item in the list, so an empty list indicates a bug.
if (unlikely(list_empty(&q->q_list_head))) {
spin_unlock_irqrestore(&q->q_lock, flags);
NVQ_WARN("_main_loop: Empty queue: q: 0x%p\n", q);
continue;
}
// Consume one item from the queue
q_item = list_first_entry(&q->q_list_head,
nv_kthread_q_item_t,
q_list_node);
list_del_init(&q_item->q_list_node);
spin_unlock_irqrestore(&q->q_lock, flags);
// Run the item
q_item->function_to_run(q_item->function_args);
// Make debugging a little simpler by clearing this between runs:
q_item = NULL;
}
while (!kthread_should_stop())
schedule();
return 0;
}
void nv_kthread_q_stop(nv_kthread_q_t *q)
{
// check if queue has been properly initialized
if (unlikely(!q->q_kthread))
return;
nv_kthread_q_flush(q);
// If this assertion fires, then a caller likely either broke the API rules,
// by adding items after calling nv_kthread_q_stop, or possibly messed up
// with inadequate flushing of self-rescheduling q_items.
if (unlikely(!list_empty(&q->q_list_head)))
NVQ_WARN("list not empty after flushing\n");
if (likely(!atomic_read(&q->main_loop_should_exit))) {
atomic_set(&q->main_loop_should_exit, 1);
// Wake up the kthread so that it can see that it needs to stop:
up(&q->q_sem);
kthread_stop(q->q_kthread);
q->q_kthread = NULL;
}
}
// When CONFIG_VMAP_STACK is defined, the kernel thread stack allocator used by
// kthread_create_on_node relies on a 2 entry, per-core cache to minimize
// vmalloc invocations. The cache is NUMA-unaware, so when there is a hit, the
// stack location ends up being a function of the core assigned to the current
// thread, instead of being a function of the specified NUMA node. The cache was
// added to the kernel in commit ac496bf48d97f2503eaa353996a4dd5e4383eaf0
// ("fork: Optimize task creation by caching two thread stacks per CPU if
// CONFIG_VMAP_STACK=y")
//
// To work around the problematic cache, we create up to three kernel threads
// -If the first thread's stack is resident on the preferred node, return this
// thread.
// -Otherwise, create a second thread. If its stack is resident on the
// preferred node, stop the first thread and return this one.
// -Otherwise, create a third thread. The stack allocator does not find a
// cached stack, and so falls back to vmalloc, which takes the NUMA hint into
// consideration. The first two threads are then stopped.
//
// When CONFIG_VMAP_STACK is not defined, the first kernel thread is returned.
//
// This function is never invoked when there is no NUMA preference (preferred
// node is NUMA_NO_NODE).
static struct task_struct *thread_create_on_node(int (*threadfn)(void *data),
nv_kthread_q_t *q,
int preferred_node,
const char *q_name)
{
unsigned i, j;
const static unsigned attempts = 3;
struct task_struct *thread[3];
for (i = 0;; i++) {
struct page *stack;
thread[i] = kthread_create_on_node(threadfn, q, preferred_node, q_name);
if (unlikely(IS_ERR(thread[i]))) {
// Instead of failing, pick the previous thread, even if its
// stack is not allocated on the preferred node.
if (i > 0)
i--;
break;
}
// vmalloc is not used to allocate the stack, so simply return the
// thread, even if its stack may not be allocated on the preferred node
if (!is_vmalloc_addr(thread[i]->stack))
break;
// Ran out of attempts - return thread even if its stack may not be
// allocated on the preferred node
if ((i == (attempts - 1)))
break;
// Get the NUMA node where the first page of the stack is resident. If
// it is the preferred node, select this thread.
stack = vmalloc_to_page(thread[i]->stack);
if (page_to_nid(stack) == preferred_node)
break;
}
for (j = i; j > 0; j--)
kthread_stop(thread[j - 1]);
return thread[i];
}
int nv_kthread_q_init_on_node(nv_kthread_q_t *q, const char *q_name, int preferred_node)
{
memset(q, 0, sizeof(*q));
INIT_LIST_HEAD(&q->q_list_head);
spin_lock_init(&q->q_lock);
sema_init(&q->q_sem, 0);
if (preferred_node == NV_KTHREAD_NO_NODE) {
q->q_kthread = kthread_create(_main_loop, q, q_name);
}
else {
q->q_kthread = thread_create_on_node(_main_loop, q, preferred_node, q_name);
}
if (IS_ERR(q->q_kthread)) {
int err = PTR_ERR(q->q_kthread);
// Clear q_kthread before returning so that nv_kthread_q_stop() can be
// safely called on it making error handling easier.
q->q_kthread = NULL;
return err;
}
wake_up_process(q->q_kthread);
return 0;
}
// Returns true (non-zero) if the item was actually scheduled, and false if the
// item was already pending in a queue.
static int _raw_q_schedule(nv_kthread_q_t *q, nv_kthread_q_item_t *q_item)
{
unsigned long flags;
int ret = 1;
spin_lock_irqsave(&q->q_lock, flags);
if (likely(list_empty(&q_item->q_list_node)))
list_add_tail(&q_item->q_list_node, &q->q_list_head);
else
ret = 0;
spin_unlock_irqrestore(&q->q_lock, flags);
if (likely(ret))
up(&q->q_sem);
return ret;
}
void nv_kthread_q_item_init(nv_kthread_q_item_t *q_item,
nv_q_func_t function_to_run,
void *function_args)
{
INIT_LIST_HEAD(&q_item->q_list_node);
q_item->function_to_run = function_to_run;
q_item->function_args = function_args;
}
// Returns true (non-zero) if the q_item got scheduled, false otherwise.
int nv_kthread_q_schedule_q_item(nv_kthread_q_t *q,
nv_kthread_q_item_t *q_item)
{
if (unlikely(atomic_read(&q->main_loop_should_exit))) {
NVQ_WARN("Not allowed: nv_kthread_q_schedule_q_item was "
"called with a non-alive q: 0x%p\n", q);
return 0;
}
return _raw_q_schedule(q, q_item);
}
static void _q_flush_function(void *args)
{
struct completion *completion = (struct completion *)args;
complete(completion);
}
static void _raw_q_flush(nv_kthread_q_t *q)
{
nv_kthread_q_item_t q_item;
DECLARE_COMPLETION(completion);
nv_kthread_q_item_init(&q_item, _q_flush_function, &completion);
_raw_q_schedule(q, &q_item);
// Wait for the flush item to run. Once it has run, then all of the
// previously queued items in front of it will have run, so that means
// the flush is complete.
wait_for_completion(&completion);
}
void nv_kthread_q_flush(nv_kthread_q_t *q)
{
if (unlikely(atomic_read(&q->main_loop_should_exit))) {
NVQ_WARN("Not allowed: nv_kthread_q_flush was called after "
"nv_kthread_q_stop. q: 0x%p\n", q);
return;
}
// This 2x flush is not a typing mistake. The queue really does have to be
// flushed twice, in order to take care of the case of a q_item that
// reschedules itself.
_raw_q_flush(q);
_raw_q_flush(q);
}