[5/9] virtio: add aio handler

Commit Message

Paolo Bonzini March 30, 2016, 12:48 p.m. UTC

From: "Michael S. Tsirkin" <[e-mail]>

In addition to handling IO in vcpu thread and
in io thread, blk dataplane introduces yet another mode:
handling it by aio.

This reuses the same handler as previous modes,
which triggers races as these were not designed to be reentrant.

As a temporary fix, add a separate handler just for aio, this will make
it possible to disable regular handlers when dataplane is active.

Signed-off-by: Michael S. Tsirkin <[e-mail]>
Signed-off-by: Paolo Bonzini <[e-mail]>
---
 hw/virtio/virtio.c         | 36 ++++++++++++++++++++++++++++++++----
 include/hw/virtio/virtio.h |  3 +++
 2 files changed, 35 insertions(+), 4 deletions(-)

Comments

Cornelia Huck March 30, 2016, 2:55 p.m. UTC | #1

On Wed, 30 Mar 2016 14:48:04 +0200
Paolo Bonzini <[e-mail]> wrote:

> From: "Michael S. Tsirkin" <[e-mail]>
> 
> In addition to handling IO in vcpu thread and
> in io thread, blk dataplane introduces yet another mode:
> handling it by aio.
> 
> This reuses the same handler as previous modes,
> which triggers races as these were not designed to be reentrant.
> 
> As a temporary fix, add a separate handler just for aio, this will make
> it possible to disable regular handlers when dataplane is active.
> 
> Signed-off-by: Michael S. Tsirkin <[e-mail]>
> Signed-off-by: Paolo Bonzini <[e-mail]>
> ---
>  hw/virtio/virtio.c         | 36 ++++++++++++++++++++++++++++++++----
>  include/hw/virtio/virtio.h |  3 +++
>  2 files changed, 35 insertions(+), 4 deletions(-)
> 

> @@ -1791,14 +1811,22 @@ void virtio_queue_aio_set_host_notifier_handler(VirtQueue *vq, AioContext *ctx,
>  {
>      if (assign && set_handler) {
>          aio_set_event_notifier(ctx, &vq->host_notifier, true,
> -                               virtio_queue_host_notifier_read);
> +                               virtio_queue_host_notifier_aio_read);
>      } else {
>          aio_set_event_notifier(ctx, &vq->host_notifier, true, NULL);
>      }
>      if (!assign) {
>          /* Test and clear notifier before after disabling event,
>           * in case poll callback didn't have time to run. */
> -        virtio_queue_host_notifier_read(&vq->host_notifier);
> +        virtio_queue_host_notifier_aio_read(&vq->host_notifier);

Is this function ever called with assign==false anymore after patch 1?

> +    }
> +}

Paolo Bonzini March 30, 2016, 3:09 p.m. UTC | #2

On 30/03/2016 16:55, Cornelia Huck wrote:
>> >      if (assign && set_handler) {
>> >          aio_set_event_notifier(ctx, &vq->host_notifier, true,
>> > -                               virtio_queue_host_notifier_read);
>> > +                               virtio_queue_host_notifier_aio_read);
>> >      } else {
>> >          aio_set_event_notifier(ctx, &vq->host_notifier, true, NULL);
>> >      }
>> >      if (!assign) {
>> >          /* Test and clear notifier before after disabling event,
>> >           * in case poll callback didn't have time to run. */
>> > -        virtio_queue_host_notifier_read(&vq->host_notifier);
>> > +        virtio_queue_host_notifier_aio_read(&vq->host_notifier);
> Is this function ever called with assign==false anymore after patch 1?

Patch 8 provides the answer (which is no :)).

Paolo

Patch

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 07c45b6..39a9f47 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -94,6 +94,7 @@  struct VirtQueue
 
     uint16_t vector;
     void (*handle_output)(VirtIODevice *vdev, VirtQueue *vq);
+    void (*handle_aio_output)(VirtIODevice *vdev, VirtQueue *vq);
     VirtIODevice *vdev;
     EventNotifier guest_notifier;
     EventNotifier host_notifier;
@@ -1086,6 +1087,16 @@  void virtio_queue_set_align(VirtIODevice *vdev, int n, int align)
     virtio_queue_update_rings(vdev, n);
 }
 
+static void virtio_queue_notify_aio_vq(VirtQueue *vq)
+{
+    if (vq->vring.desc && vq->handle_aio_output) {
+        VirtIODevice *vdev = vq->vdev;
+
+        trace_virtio_queue_notify(vdev, vq - vdev->vq, vq);
+        vq->handle_aio_output(vdev, vq);
+    }
+}
+
 static void virtio_queue_notify_vq(VirtQueue *vq)
 {
     if (vq->vring.desc && vq->handle_output) {
@@ -1141,10 +1152,19 @@  VirtQueue *virtio_add_queue(VirtIODevice *vdev, int queue_size,
     vdev->vq[i].vring.num_default = queue_size;
     vdev->vq[i].vring.align = VIRTIO_PCI_VRING_ALIGN;
     vdev->vq[i].handle_output = handle_output;
+    vdev->vq[i].handle_aio_output = NULL;
 
     return &vdev->vq[i];
 }
 
+void virtio_set_queue_aio(VirtQueue *vq,
+                          void (*handle_output)(VirtIODevice *, VirtQueue *))
+{
+    assert(vq->handle_output);
+
+    vq->handle_aio_output = handle_output;
+}
+
 void virtio_del_queue(VirtIODevice *vdev, int n)
 {
     if (n < 0 || n >= VIRTIO_QUEUE_MAX) {
@@ -1778,11 +1798,11 @@  EventNotifier *virtio_queue_get_guest_notifier(VirtQueue *vq)
     return &vq->guest_notifier;
 }
 
-static void virtio_queue_host_notifier_read(EventNotifier *n)
+static void virtio_queue_host_notifier_aio_read(EventNotifier *n)
 {
     VirtQueue *vq = container_of(n, VirtQueue, host_notifier);
     if (event_notifier_test_and_clear(n)) {
-        virtio_queue_notify_vq(vq);
+        virtio_queue_notify_aio_vq(vq);
     }
 }
 
@@ -1791,14 +1811,22 @@  void virtio_queue_aio_set_host_notifier_handler(VirtQueue *vq, AioContext *ctx,
 {
     if (assign && set_handler) {
         aio_set_event_notifier(ctx, &vq->host_notifier, true,
-                               virtio_queue_host_notifier_read);
+                               virtio_queue_host_notifier_aio_read);
     } else {
         aio_set_event_notifier(ctx, &vq->host_notifier, true, NULL);
     }
     if (!assign) {
         /* Test and clear notifier before after disabling event,
          * in case poll callback didn't have time to run. */
-        virtio_queue_host_notifier_read(&vq->host_notifier);
+        virtio_queue_host_notifier_aio_read(&vq->host_notifier);
+    }
+}
+
+static void virtio_queue_host_notifier_read(EventNotifier *n)
+{
+    VirtQueue *vq = container_of(n, VirtQueue, host_notifier);
+    if (event_notifier_test_and_clear(n)) {
+        virtio_queue_notify_vq(vq);
     }
 }
 
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index 5afb51c..fa3f93b 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -142,6 +142,9 @@  VirtQueue *virtio_add_queue(VirtIODevice *vdev, int queue_size,
                             void (*handle_output)(VirtIODevice *,
                                                   VirtQueue *));
 
+void virtio_set_queue_aio(VirtQueue *vq,
+                          void (*handle_output)(VirtIODevice *, VirtQueue *));
+
 void virtio_del_queue(VirtIODevice *vdev, int n);
 
 void *virtqueue_alloc_element(size_t sz, unsigned out_num, unsigned in_num);