[PATCH] virtio_ring: Use workqueue to execute virtqueue callback

[PATCH] virtio_ring: Use workqueue to execute virtqueue callback

[Clement Leger]

Currently, in vring_interrupt, the vq callbacks are called directly.
However, these callbacks are not meant to be executed in IRQ context.
They do not return any irq_return_t value and some of them can do
locking (rpmsg_recv_done -> rpmsg_recv_single -> mutex_lock).
When compiled with DEBUG_ATOMIC_SLEEP, the kernel will spit out warnings
when such case shappen.

In order to allow calling these callbacks safely (without sleeping in
IRQ context), execute them in a workqueue if needed.

Signed-off-by: Clement Leger <cleger@kalray.eu>
---
 drivers/virtio/virtio_ring.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 867c7ebd3f10..0e4d0e5ca227 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -183,6 +183,9 @@ struct vring_virtqueue {
 	/* DMA, allocation, and size information */
 	bool we_own_ring;
 
+	/* Work struct for vq callback handling */
+	struct work_struct work;
+
 #ifdef DEBUG
 	/* They're supposed to lock for us. */
 	unsigned int in_use;
@@ -2029,6 +2032,16 @@ static inline bool more_used(const struct vring_virtqueue *vq)
 	return vq->packed_ring ? more_used_packed(vq) : more_used_split(vq);
 }
 
+static void vring_work_handler(struct work_struct *work_struct)
+{
+	struct vring_virtqueue *vq = container_of(work_struct,
+						  struct vring_virtqueue,
+						  work);
+	pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback);
+
+	vq->vq.callback(&vq->vq);
+}
+
 irqreturn_t vring_interrupt(int irq, void *_vq)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
@@ -2041,9 +2054,8 @@ irqreturn_t vring_interrupt(int irq, void *_vq)
 	if (unlikely(vq->broken))
 		return IRQ_HANDLED;
 
-	pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback);
 	if (vq->vq.callback)
-		vq->vq.callback(&vq->vq);
+		schedule_work(&vq->work);
 
 	return IRQ_HANDLED;
 }
@@ -2110,6 +2122,8 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
 					vq->split.avail_flags_shadow);
 	}
 
+	INIT_WORK(&vq->work, vring_work_handler);
+
 	vq->split.desc_state = kmalloc_array(vring.num,
 			sizeof(struct vring_desc_state_split), GFP_KERNEL);
 	if (!vq->split.desc_state) {
@@ -2179,6 +2193,8 @@ void vring_del_virtqueue(struct virtqueue *_vq)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
 
+	cancel_work_sync(&vq->work);
+
 	if (vq->we_own_ring) {
 		if (vq->packed_ring) {
 			vring_free_queue(vq->vq.vdev,
-- 
2.15.0.276.g89ea799

Re: [PATCH] virtio_ring: Use workqueue to execute virtqueue callback

[Michael S. Tsirkin]

On Wed, Jan 15, 2020 at 01:05:35PM +0100, Clement Leger wrote:
> Currently, in vring_interrupt, the vq callbacks are called directly.
> However, these callbacks are not meant to be executed in IRQ context.
> They do not return any irq_return_t value and some of them can do
> locking (rpmsg_recv_done -> rpmsg_recv_single -> mutex_lock).

That's a bug in rpmsg. Pls fix there.

> When compiled with DEBUG_ATOMIC_SLEEP, the kernel will spit out warnings
> when such case shappen.
> 
> In order to allow calling these callbacks safely (without sleeping in
> IRQ context), execute them in a workqueue if needed.
> 
> Signed-off-by: Clement Leger <cleger@kalray.eu>

If applied this would slow data path handling of VQ events
significantly. Teaching callbacks to return irqreturn_t
might be a good idea, though it's not an insignificant
amount of work.


> ---
>  drivers/virtio/virtio_ring.c | 20 ++++++++++++++++++--
>  1 file changed, 18 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 867c7ebd3f10..0e4d0e5ca227 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -183,6 +183,9 @@ struct vring_virtqueue {
>  	/* DMA, allocation, and size information */
>  	bool we_own_ring;
>  
> +	/* Work struct for vq callback handling */
> +	struct work_struct work;
> +
>  #ifdef DEBUG
>  	/* They're supposed to lock for us. */
>  	unsigned int in_use;
> @@ -2029,6 +2032,16 @@ static inline bool more_used(const struct vring_virtqueue *vq)
>  	return vq->packed_ring ? more_used_packed(vq) : more_used_split(vq);
>  }
>  
> +static void vring_work_handler(struct work_struct *work_struct)
> +{
> +	struct vring_virtqueue *vq = container_of(work_struct,
> +						  struct vring_virtqueue,
> +						  work);
> +	pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback);
> +
> +	vq->vq.callback(&vq->vq);
> +}
> +
>  irqreturn_t vring_interrupt(int irq, void *_vq)
>  {
>  	struct vring_virtqueue *vq = to_vvq(_vq);
> @@ -2041,9 +2054,8 @@ irqreturn_t vring_interrupt(int irq, void *_vq)
>  	if (unlikely(vq->broken))
>  		return IRQ_HANDLED;
>  
> -	pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback);
>  	if (vq->vq.callback)
> -		vq->vq.callback(&vq->vq);
> +		schedule_work(&vq->work);
>  
>  	return IRQ_HANDLED;
>  }
> @@ -2110,6 +2122,8 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
>  					vq->split.avail_flags_shadow);
>  	}
>  
> +	INIT_WORK(&vq->work, vring_work_handler);
> +
>  	vq->split.desc_state = kmalloc_array(vring.num,
>  			sizeof(struct vring_desc_state_split), GFP_KERNEL);
>  	if (!vq->split.desc_state) {
> @@ -2179,6 +2193,8 @@ void vring_del_virtqueue(struct virtqueue *_vq)
>  {
>  	struct vring_virtqueue *vq = to_vvq(_vq);
>  
> +	cancel_work_sync(&vq->work);
> +
>  	if (vq->we_own_ring) {
>  		if (vq->packed_ring) {
>  			vring_free_queue(vq->vq.vdev,
> -- 
> 2.15.0.276.g89ea799

Re: [PATCH] virtio_ring: Use workqueue to execute virtqueue callback

[Clément Leger]

----- On 15 Jan, 2020, at 14:49, Michael S. Tsirkin mst@redhat.com wrote:

> On Wed, Jan 15, 2020 at 01:05:35PM +0100, Clement Leger wrote:
>> Currently, in vring_interrupt, the vq callbacks are called directly.
>> However, these callbacks are not meant to be executed in IRQ context.
>> They do not return any irq_return_t value and some of them can do
>> locking (rpmsg_recv_done -> rpmsg_recv_single -> mutex_lock).
> 
> That's a bug in rpmsg. Pls fix there.

Ok.

> 
>> When compiled with DEBUG_ATOMIC_SLEEP, the kernel will spit out warnings
>> when such case shappen.
>> 
>> In order to allow calling these callbacks safely (without sleeping in
>> IRQ context), execute them in a workqueue if needed.
>> 
>> Signed-off-by: Clement Leger <cleger@kalray.eu>
> 
> If applied this would slow data path handling of VQ events
> significantly. Teaching callbacks to return irqreturn_t
> might be a good idea, though it's not an insignificant
> amount of work.

Yes, I was expecting that it would slow down VQ event handling.
I was not completely sure of the criticality of that.

Thanks for your answer.

> 
> 
>> ---
>>  drivers/virtio/virtio_ring.c | 20 ++++++++++++++++++--
>>  1 file changed, 18 insertions(+), 2 deletions(-)
>> 
>> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
>> index 867c7ebd3f10..0e4d0e5ca227 100644
>> --- a/drivers/virtio/virtio_ring.c
>> +++ b/drivers/virtio/virtio_ring.c
>> @@ -183,6 +183,9 @@ struct vring_virtqueue {
>>  	/* DMA, allocation, and size information */
>>  	bool we_own_ring;
>>  
>> +	/* Work struct for vq callback handling */
>> +	struct work_struct work;
>> +
>>  #ifdef DEBUG
>>  	/* They're supposed to lock for us. */
>>  	unsigned int in_use;
>> @@ -2029,6 +2032,16 @@ static inline bool more_used(const struct vring_virtqueue
>> *vq)
>>  	return vq->packed_ring ? more_used_packed(vq) : more_used_split(vq);
>>  }
>>  
>> +static void vring_work_handler(struct work_struct *work_struct)
>> +{
>> +	struct vring_virtqueue *vq = container_of(work_struct,
>> +						  struct vring_virtqueue,
>> +						  work);
>> +	pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback);
>> +
>> +	vq->vq.callback(&vq->vq);
>> +}
>> +
>>  irqreturn_t vring_interrupt(int irq, void *_vq)
>>  {
>>  	struct vring_virtqueue *vq = to_vvq(_vq);
>> @@ -2041,9 +2054,8 @@ irqreturn_t vring_interrupt(int irq, void *_vq)
>>  	if (unlikely(vq->broken))
>>  		return IRQ_HANDLED;
>>  
>> -	pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback);
>>  	if (vq->vq.callback)
>> -		vq->vq.callback(&vq->vq);
>> +		schedule_work(&vq->work);
>>  
>>  	return IRQ_HANDLED;
>>  }
>> @@ -2110,6 +2122,8 @@ struct virtqueue *__vring_new_virtqueue(unsigned int
>> index,
>>  					vq->split.avail_flags_shadow);
>>  	}
>>  
>> +	INIT_WORK(&vq->work, vring_work_handler);
>> +
>>  	vq->split.desc_state = kmalloc_array(vring.num,
>>  			sizeof(struct vring_desc_state_split), GFP_KERNEL);
>>  	if (!vq->split.desc_state) {
>> @@ -2179,6 +2193,8 @@ void vring_del_virtqueue(struct virtqueue *_vq)
>>  {
>>  	struct vring_virtqueue *vq = to_vvq(_vq);
>>  
>> +	cancel_work_sync(&vq->work);
>> +
>>  	if (vq->we_own_ring) {
>>  		if (vq->packed_ring) {
>>  			vring_free_queue(vq->vq.vdev,
>> --
> > 2.15.0.276.g89ea799