On 5/31/23 10:15 AM, Mike Christie wrote:
>>> rcu would work for your case and for what Jason had requested.
>> Yeah, so you already have some patches?
>>
>> Do you want to send it to solve this problem?
>>
> Yeah, I'll break them out and send them later today when I can retest
> rebased patches.
>
Just one question. Do you core vhost developers consider RCU more complex
or switching to READ_ONCE/WRITE_ONCE? I am asking because for this immediate
regression fix we could just switch to the latter like below to just fix
the crash if we think that is more simple.
I think RCU is just a little more complex/invasive because it will have the
extra synchronize_rcu calls.
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index a92af08e7864..03fd47a22a73 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -235,7 +235,7 @@ void vhost_dev_flush(struct vhost_dev *dev)
{
struct vhost_flush_struct flush;
- if (dev->worker) {
+ if (READ_ONCE(dev->worker.vtsk)) {
init_completion(&flush.wait_event);
vhost_work_init(&flush.work, vhost_flush_work);
@@ -247,7 +247,9 @@ EXPORT_SYMBOL_GPL(vhost_dev_flush);
void vhost_work_queue(struct vhost_dev *dev, struct vhost_work *work)
{
- if (!dev->worker)
+ struct vhost_task *vtsk = READ_ONCE(dev->worker.vtsk);
+
+ if (!vtsk)
return;
if (!test_and_set_bit(VHOST_WORK_QUEUED, &work->flags)) {
@@ -255,8 +257,8 @@ void vhost_work_queue(struct vhost_dev *dev, struct vhost_work *work)
* sure it was not in the list.
* test_and_set_bit() implies a memory barrier.
*/
- llist_add(&work->node, &dev->worker->work_list);
- wake_up_process(dev->worker->vtsk->task);
+ llist_add(&work->node, &dev->worker.work_list);
+ wake_up_process(vtsk->task);
}
}
EXPORT_SYMBOL_GPL(vhost_work_queue);
@@ -264,7 +266,7 @@ EXPORT_SYMBOL_GPL(vhost_work_queue);
/* A lockless hint for busy polling code to exit the loop */
bool vhost_has_work(struct vhost_dev *dev)
{
- return dev->worker && !llist_empty(&dev->worker->work_list);
+ return !llist_empty(&dev->worker.work_list);
}
EXPORT_SYMBOL_GPL(vhost_has_work);
@@ -468,7 +470,7 @@ void vhost_dev_init(struct vhost_dev *dev,
dev->umem = NULL;
dev->iotlb = NULL;
dev->mm = NULL;
- dev->worker = NULL;
+ memset(&dev->worker, 0, sizeof(dev->worker));
dev->iov_limit = iov_limit;
dev->weight = weight;
dev->byte_weight = byte_weight;
@@ -542,46 +544,38 @@ static void vhost_detach_mm(struct vhost_dev *dev)
static void vhost_worker_free(struct vhost_dev *dev)
{
- struct vhost_worker *worker = dev->worker;
+ struct vhost_task *vtsk = READ_ONCE(dev->worker.vtsk);
- if (!worker)
+ if (!vtsk)
return;
- dev->worker = NULL;
- WARN_ON(!llist_empty(&worker->work_list));
- vhost_task_stop(worker->vtsk);
- kfree(worker);
+ vhost_task_stop(vtsk);
+ WARN_ON(!llist_empty(&dev->worker.work_list));
+ WRITE_ONCE(dev->worker.vtsk, NULL);
}
static int vhost_worker_create(struct vhost_dev *dev)
{
- struct vhost_worker *worker;
struct vhost_task *vtsk;
char name[TASK_COMM_LEN];
int ret;
- worker = kzalloc(sizeof(*worker), GFP_KERNEL_ACCOUNT);
- if (!worker)
- return -ENOMEM;
-
- dev->worker = worker;
- worker->kcov_handle = kcov_common_handle();
- init_llist_head(&worker->work_list);
+ dev->worker.kcov_handle = kcov_common_handle();
+ init_llist_head(&dev->worker.work_list);
snprintf(name, sizeof(name), "vhost-%d", current->pid);
- vtsk = vhost_task_create(vhost_worker, worker, name);
+ vtsk = vhost_task_create(vhost_worker, &dev->worker, name);
if (!vtsk) {
ret = -ENOMEM;
goto free_worker;
}
- worker->vtsk = vtsk;
+ WRITE_ONCE(dev->worker.vtsk, vtsk);
vhost_task_start(vtsk);
return 0;
free_worker:
- kfree(worker);
- dev->worker = NULL;
+ WRITE_ONCE(dev->worker.vtsk, NULL);
return ret;
}
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 0308638cdeee..305ec8593d46 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -154,7 +154,7 @@ struct vhost_dev {
struct vhost_virtqueue **vqs;
int nvqs;
struct eventfd_ctx *log_ctx;
- struct vhost_worker *worker;
+ struct vhost_worker worker;
struct vhost_iotlb *umem;
struct vhost_iotlb *iotlb;
spinlock_t iotlb_lock;
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