Re: [PATCH v4 04/25] virtio: defer config changed notifications
From: Rusty Russell <hidden>
Date: 2014-10-14 06:53:59
Also in:
kvm, linux-s390, linux-scsi, lkml, virtualization
Subsystem:
the rest, virtio core · Maintainers:
Linus Torvalds, "Michael S. Tsirkin", Jason Wang
"Michael S. Tsirkin" [off-list ref] writes:
Defer config changed notifications that arrive during probe/scan/freeze/restore. This will allow drivers to set DRIVER_OK earlier, without worrying about racing with config change interrupts. This change will also benefit old hypervisors (before 2009) that send interrupts without checking DRIVER_OK: previously, the callback could race with driver-specific initialization. This will also help simplify drivers.
But AFAICT you never *read* dev->config_changed. You unconditionally trigger a config_changed event in virtio_config_enable(). That's a bit weird, but probably OK. How about the following change (on top of your patch). I think the renaming is clearer, and note the added if() test in virtio_config_enable(). If you approve, I'll fold it in. Cheers, Rusty.
diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index 2536701b098b..df598dd8c5c8 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c@@ -122,7 +122,7 @@ static void __virtio_config_changed(struct virtio_device *dev) struct virtio_driver *drv = drv_to_virtio(dev->dev.driver); if (!dev->config_enabled) - dev->config_changed = true; + dev->config_change_pending = true; else if (drv && drv->config_changed) drv->config_changed(dev); }
@@ -148,8 +148,9 @@ static void virtio_config_enable(struct virtio_device *dev) { spin_lock_irq(&dev->config_lock); dev->config_enabled = true; - __virtio_config_changed(dev); - dev->config_changed = false; + if (dev->config_change_pending) + __virtio_config_changed(dev); + dev->config_change_pending = false; spin_unlock_irq(&dev->config_lock); }
@@ -253,7 +254,7 @@ int register_virtio_device(struct virtio_device *dev) spin_lock_init(&dev->config_lock); dev->config_enabled = false; - dev->config_changed = false; + dev->config_change_pending = false; /* We always start by resetting the device, in case a previous * driver messed it up. This also tests that code path a little. */
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 5636b119dc25..65261a7244fc 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h@@ -80,7 +80,7 @@ bool virtqueue_is_broken(struct virtqueue *vq); * @index: unique position on the virtio bus * @failed: saved value for CONFIG_S_FAILED bit (for restore) * @config_enabled: configuration change reporting enabled - * @config_changed: configuration change reported while disabled + * @config_change_pending: configuration change reported while disabled * @config_lock: protects configuration change reporting * @dev: underlying device. * @id: the device type identification (used to match it with a driver).
@@ -94,7 +94,7 @@ struct virtio_device { int index; bool failed; bool config_enabled; - bool config_changed; + bool config_change_pending; spinlock_t config_lock; struct device dev; struct virtio_device_id id;