Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
To:     Dominique Martinet <asmadeus@codewreck.org>
CC:     "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        "Eric Van Hensbergen" <ericvh@gmail.com>,
        Ron Minnich <rminnich@sandia.gov>,
        "Latchesar Ionkov" <lucho@ionkov.net>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        <v9fs-developer@lists.sourceforge.net>
From:   piaojun <piaojun@huawei.com>
Subject: [PATCH] net/9p/trans_virtio.c: replace mutex_lock with spin_lock to
 protect 'virtio_chan_list'
Message-ID: <5B4EF511.7090104@huawei.com>
Date:   Wed, 18 Jul 2018 16:06:41 +0800
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101
 Thunderbird/38.2.0
MIME-Version: 1.0
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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 <piaojun@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);
--