[PATCH v4 1/3] virtio-balloon: tweak config_changed implementation

Wei Wang
2019-01-08T04:50:03Z

virtio-ccw has deadlock issues with reading the config space inside the
interrupt context, so we tweak the virtballoon_changed implementation
by moving the config read operations into the related workqueue contexts.
The config_read_bitmap is used as a flag to the workqueue callbacks
about the related config fields that need to be read.

The cmd_id_received is also renamed to cmd_id_received_cache, and
the value should be obtained via virtio_balloon_cmd_id_received.

Fixes: 86a559787e6f ("virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT")
Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Wei Wang <wei.w.wang@intel.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
---
drivers/virtio/virtio_balloon.c | 98 +++++++++++++++++++++++++++--------------
1 file changed, 65 insertions(+), 33 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 728ecd1..45d32f5 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -61,6 +61,10 @@ enum virtio_balloon_vq {
VIRTIO_BALLOON_VQ_MAX
};

+enum virtio_balloon_config_read {
+ VIRTIO_BALLOON_CONFIG_READ_CMD_ID = 0,
+};
+
struct virtio_balloon {
struct virtio_device *vdev;
struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *free_page_vq;
@@ -77,14 +81,20 @@ struct virtio_balloon {
/* Prevent updating balloon when it is being canceled. */
spinlock_t stop_update_lock;
bool stop_update;
+ /* Bitmap to indicate if reading the related config fields are needed */
+ unsigned long config_read_bitmap;

/* The list of allocated free pages, waiting to be given back to mm */
struct list_head free_page_list;
spinlock_t free_page_list_lock;
/* The number of free page blocks on the above list */
unsigned long num_free_page_blocks;
- /* The cmd id received from host */
- u32 cmd_id_received;
+ /*
+ * The cmd id received from host.
+ * Read it via virtio_balloon_cmd_id_received to get the latest value
+ * sent from host.
+ */
+ u32 cmd_id_received_cache;
/* The cmd id that is actively in use */
__virtio32 cmd_id_active;
/* Buffer to store the stop sign */
@@ -390,37 +400,31 @@ static unsigned long return_free_pages_to_mm(struct virtio_balloon *vb,
return num_returned;
}

+static void virtio_balloon_queue_free_page_work(struct virtio_balloon *vb)
+{
+ if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
+ return;
+
+ /* No need to queue the work if the bit was already set. */
+ if (test_and_set_bit(VIRTIO_BALLOON_CONFIG_READ_CMD_ID,
+ &vb->config_read_bitmap))
+ return;
+
+ queue_work(vb->balloon_wq, &vb->report_free_page_work);
+}
+
static void virtballoon_changed(struct virtio_device *vdev)
{
struct virtio_balloon *vb = vdev->priv;
unsigned long flags;
- s64 diff = towards_target(vb);
-
- if (diff) {
- spin_lock_irqsave(&vb->stop_update_lock, flags);
- if (!vb->stop_update)
- queue_work(system_freezable_wq,
- &vb->update_balloon_size_work);
- spin_unlock_irqrestore(&vb->stop_update_lock, flags);
- }

- if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
- virtio_cread(vdev, struct virtio_balloon_config,
- free_page_report_cmd_id, &vb->cmd_id_received);
- if (vb->cmd_id_received == VIRTIO_BALLOON_CMD_ID_DONE) {
- /* Pass ULONG_MAX to give back all the free pages */
- return_free_pages_to_mm(vb, ULONG_MAX);
- } else if (vb->cmd_id_received != VIRTIO_BALLOON_CMD_ID_STOP &&
- vb->cmd_id_received !=
- virtio32_to_cpu(vdev, vb->cmd_id_active)) {
- spin_lock_irqsave(&vb->stop_update_lock, flags);
- if (!vb->stop_update) {
- queue_work(vb->balloon_wq,
- &vb->report_free_page_work);
- }
- spin_unlock_irqrestore(&vb->stop_update_lock, flags);
- }
+ spin_lock_irqsave(&vb->stop_update_lock, flags);
+ if (!vb->stop_update) {
+ queue_work(system_freezable_wq,
+ &vb->update_balloon_size_work);
+ virtio_balloon_queue_free_page_work(vb);
}
+ spin_unlock_irqrestore(&vb->stop_update_lock, flags);
}

static void update_balloon_size(struct virtio_balloon *vb)
@@ -527,6 +531,17 @@ static int init_vqs(struct virtio_balloon *vb)
return 0;
}

+static u32 virtio_balloon_cmd_id_received(struct virtio_balloon *vb)
+{
+ if (test_and_clear_bit(VIRTIO_BALLOON_CONFIG_READ_CMD_ID,
+ &vb->config_read_bitmap))
+ virtio_cread(vb->vdev, struct virtio_balloon_config,
+ free_page_report_cmd_id,
+ &vb->cmd_id_received_cache);
+
+ return vb->cmd_id_received_cache;
+}
+
static int send_cmd_id_start(struct virtio_balloon *vb)
{
struct scatterlist sg;
@@ -537,7 +552,8 @@ static int send_cmd_id_start(struct virtio_balloon *vb)
while (virtqueue_get_buf(vq, &unused))
;

- vb->cmd_id_active = cpu_to_virtio32(vb->vdev, vb->cmd_id_received);
+ vb->cmd_id_active = cpu_to_virtio32(vb->vdev,
+ virtio_balloon_cmd_id_received(vb));
sg_init_one(&sg, &vb->cmd_id_active, sizeof(vb->cmd_id_active));
err = virtqueue_add_outbuf(vq, &sg, 1, &vb->cmd_id_active, GFP_KERNEL);
if (!err)
@@ -620,7 +636,8 @@ static int send_free_pages(struct virtio_balloon *vb)
* stop the reporting.
*/
cmd_id_active = virtio32_to_cpu(vb->vdev, vb->cmd_id_active);
- if (cmd_id_active != vb->cmd_id_received)
+ if (unlikely(cmd_id_active !=
+ virtio_balloon_cmd_id_received(vb)))
break;

/*
@@ -637,11 +654,9 @@ static int send_free_pages(struct virtio_balloon *vb)
return 0;
}

-static void report_free_page_func(struct work_struct *work)
+static void virtio_balloon_report_free_page(struct virtio_balloon *vb)
{
int err;
- struct virtio_balloon *vb = container_of(work, struct virtio_balloon,
- report_free_page_work);
struct device *dev = &vb->vdev->dev;

/* Start by sending the received cmd id to host with an outbuf. */
@@ -659,6 +674,23 @@ static void report_free_page_func(struct work_struct *work)
dev_err(dev, "Failed to send a stop id, err = %d\n", err);
}

+static void report_free_page_func(struct work_struct *work)
+{
+ struct virtio_balloon *vb = container_of(work, struct virtio_balloon,
+ report_free_page_work);
+ u32 cmd_id_received;
+
+ cmd_id_received = virtio_balloon_cmd_id_received(vb);
+ if (cmd_id_received == VIRTIO_BALLOON_CMD_ID_DONE) {
+ /* Pass ULONG_MAX to give back all the free pages */
+ return_free_pages_to_mm(vb, ULONG_MAX);
+ } else if (cmd_id_received != VIRTIO_BALLOON_CMD_ID_STOP &&
+ cmd_id_received !=
+ virtio32_to_cpu(vb->vdev, vb->cmd_id_active)) {
+ virtio_balloon_report_free_page(vb);
+ }
+}
+
#ifdef CONFIG_BALLOON_COMPACTION
/*
* virtballoon_migratepage - perform the balloon page migration on behalf of
@@ -885,7 +917,7 @@ static int virtballoon_probe(struct virtio_device *vdev)
goto out_del_vqs;
}
INIT_WORK(&vb->report_free_page_work, report_free_page_func);
- vb->cmd_id_received = VIRTIO_BALLOON_CMD_ID_STOP;
+ vb->cmd_id_received_cache = VIRTIO_BALLOON_CMD_ID_STOP;
vb->cmd_id_active = cpu_to_virtio32(vb->vdev,
VIRTIO_BALLOON_CMD_ID_STOP);
vb->cmd_id_stop = cpu_to_virtio32(vb->vdev,
--
2.7.4