Re: [PATCH] vhost vdpa: fix the irq check for invoking irq_bypass_unregister_producer

When qemu with vhost-vdpa netdevice is run for the first time, it works well.
But after the VM is powered off, the next qemu run causes kernel panic due to
a NULL pointer dereference in irq_bypass_register_producer().

When the VM is powered off, vhost_vdpa_clean_irq() misses on calling
irq_bypass_unregister_producer() for irq 0 because of the existing check.

This leaves stale producer nodes, which are reset in vhost_vring_call_reset()
when vhost_dev_init() is invoked during the second qemu run.

As the node member of struct irq_bypass_producer is also initialized
to zero, traversal on the producers list causes crash due to NULL pointer
dereference.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=211711
Signed-off-by: Gautam Dawar <gdawar@xilinx.com <mailto:gdawar@xilinx.com>>

diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
index 62a9bb0efc55..d1c3a33c6239 100644
--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c

@@ -849,7 +849,7 @@ static void vhost_vdpa_clean_irq(struct vhost_vdpa *v)

        for (i = 0; i < v->nvqs; i++) {
                vq = &v->vqs[i];
-               if (vq->call_ctx.producer.irq)
+               if (vq->call_ctx.producer.irq >= 0)
irq_bypass_unregister_producer(&vq->call_ctx.producer);