[PATCH] net/9p/trans_virtio.c: replace mutex_lock with spin_lock to protect 'virtio_chan_list'

[piaojun]

spin_lock is more effective for short time protection than mutex_lock, as
mutex lock may cause process sleep and wake up which consume much cpu
time.

Signed-off-by: Jun Piao <piao...@huawei.com>
---
 net/9p/trans_virtio.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index 86077f7..7ec0dbf 100644
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -53,8 +53,8 @@

 #define VIRTQUEUE_NUM  128

-/* a single mutex to manage channel initialization and attachment */
-static DEFINE_MUTEX(virtio_9p_lock);
+/* a single spinlock to manage channel initialization and attachment */
+static DEFINE_SPINLOCK(virtio_9p_lock);
 static DECLARE_WAIT_QUEUE_HEAD(vp_wq);
 static atomic_t vp_pinned = ATOMIC_INIT(0);

@@ -120,10 +120,10 @@ static void p9_virtio_close(struct p9_client *client)
 {
        struct virtio_chan *chan = client->trans;

-       mutex_lock(&virtio_9p_lock);
+       spin_lock(&virtio_9p_lock);
        if (chan)
                chan->inuse = false;
-       mutex_unlock(&virtio_9p_lock);
+       spin_unlock(&virtio_9p_lock);
 }

 /**
@@ -605,9 +605,9 @@ static int p9_virtio_probe(struct virtio_device *vdev)

        virtio_device_ready(vdev);

-       mutex_lock(&virtio_9p_lock);
+       spin_lock(&virtio_9p_lock);
        list_add_tail(&chan->chan_list, &virtio_chan_list);
-       mutex_unlock(&virtio_9p_lock);
+       spin_unlock(&virtio_9p_lock);

        /* Let udev rules use the new mount_tag attribute. */
        kobject_uevent(&(vdev->dev.kobj), KOBJ_CHANGE);
@@ -645,7 +645,7 @@ static int p9_virtio_probe(struct virtio_device *vdev)
        int ret = -ENOENT;
        int found = 0;

-       mutex_lock(&virtio_9p_lock);
+       spin_lock(&virtio_9p_lock);
        list_for_each_entry(chan, &virtio_chan_list, chan_list) {
                if (!strncmp(devname, chan->tag, chan->tag_len) &&
                    strlen(devname) == chan->tag_len) {
@@ -657,7 +657,7 @@ static int p9_virtio_probe(struct virtio_device *vdev)
                        ret = -EBUSY;
                }
        }
-       mutex_unlock(&virtio_9p_lock);
+       spin_unlock(&virtio_9p_lock);

        if (!found) {
                pr_err("no channels available for device %s\n", devname);
@@ -682,7 +682,7 @@ static void p9_virtio_remove(struct virtio_device *vdev)
        struct virtio_chan *chan = vdev->priv;
        unsigned long warning_time;

-       mutex_lock(&virtio_9p_lock);
+       spin_lock(&virtio_9p_lock);

        /* Remove self from list so we don't get new users. */
        list_del(&chan->chan_list);
@@ -690,17 +690,17 @@ static void p9_virtio_remove(struct virtio_device *vdev)

        /* Wait for existing users to close. */
        while (chan->inuse) {
-               mutex_unlock(&virtio_9p_lock);
+               spin_unlock(&virtio_9p_lock);
                msleep(250);
                if (time_after(jiffies, warning_time + 10 * HZ)) {
                        dev_emerg(&vdev->dev,
                                  "p9_virtio_remove: waiting for device in 
use.\n");
                        warning_time = jiffies;
                }
-               mutex_lock(&virtio_9p_lock);
+               spin_lock(&virtio_9p_lock);
        }

-       mutex_unlock(&virtio_9p_lock);
+       spin_unlock(&virtio_9p_lock);

        vdev->config->reset(vdev);
        vdev->config->del_vqs(vdev);
--