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* potential race in virtio ring?
@ 2010-06-14 13:59 ` Michael S. Tsirkin
  0 siblings, 0 replies; 3+ messages in thread
From: Michael S. Tsirkin @ 2010-06-14 13:59 UTC (permalink / raw)
  To: virtualization, Rusty Russell, Jiri Pirko, Shirley Ma, netdev,
	linux-kernel

Hi!
I was going over the vring code and noticed, that
the ring has this check:

irqreturn_t vring_interrupt(int irq, void *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);
        
        if (!more_used(vq)) {
                pr_debug("virtqueue interrupt with no work for %p\n", vq);
                return IRQ_NONE;


static inline bool more_used(const struct vring_virtqueue *vq)
{               
        return vq->last_used_idx != vq->vring.used->idx;
}               

My concern is that with virtio net, more_used is called
on a CPU different from the one that polls the vq.
This might mean that last_used_idx value might be stale.
Could this lead to a missed interrupt?

Thanks,

-- 
MST

^ permalink raw reply	[flat|nested] 3+ messages in thread
* potential race in virtio ring?
@ 2010-06-14 13:59 ` Michael S. Tsirkin
  0 siblings, 0 replies; 3+ messages in thread
From: Michael S. Tsirkin @ 2010-06-14 13:59 UTC (permalink / raw)
  To: virtualization, Rusty Russell, Jiri Pirko, Shirley Ma, netdev,
	linux-kernel

Hi!
I was going over the vring code and noticed, that
the ring has this check:

irqreturn_t vring_interrupt(int irq, void *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);
        
        if (!more_used(vq)) {
                pr_debug("virtqueue interrupt with no work for %p\n", vq);
                return IRQ_NONE;


static inline bool more_used(const struct vring_virtqueue *vq)
{               
        return vq->last_used_idx != vq->vring.used->idx;
}               

My concern is that with virtio net, more_used is called
on a CPU different from the one that polls the vq.
This might mean that last_used_idx value might be stale.
Could this lead to a missed interrupt?

Thanks,

-- 
MST

^ permalink raw reply	[flat|nested] 3+ messages in thread
* potential race in virtio ring?
@ 2010-06-14 13:59 Michael S. Tsirkin
  0 siblings, 0 replies; 3+ messages in thread
From: Michael S. Tsirkin @ 2010-06-14 13:59 UTC (permalink / raw)
  To: virtualization, Rusty Russell, Jiri Pirko, Shirley Ma, netdev

Hi!
I was going over the vring code and noticed, that
the ring has this check:

irqreturn_t vring_interrupt(int irq, void *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);
        
        if (!more_used(vq)) {
                pr_debug("virtqueue interrupt with no work for %p\n", vq);
                return IRQ_NONE;


static inline bool more_used(const struct vring_virtqueue *vq)
{               
        return vq->last_used_idx != vq->vring.used->idx;
}               

My concern is that with virtio net, more_used is called
on a CPU different from the one that polls the vq.
This might mean that last_used_idx value might be stale.
Could this lead to a missed interrupt?

Thanks,

-- 
MST

^ permalink raw reply	[flat|nested] 3+ messages in thread
end of thread, other threads:[~2010-06-14 14:04 UTC | newest]

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2010-06-14 13:59 Michael S. Tsirkin

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