linux-kernel - [42/74] virtio: console: add locking around c

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Date:	Sun, 07 Apr 2013 23:45:42 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Wanlong Gao" <gaowanlong@...fujitsu.com>,
	"Rusty Russell" <rusty@...tcorp.com.au>,
	"FuXiangChun" <xfu@...hat.com>, "Amit Shah" <amit.shah@...hat.com>,
	"Asias He" <asias@...hat.com>
Subject: [42/74] virtio: console: add locking around c_ovq operations

3.2.43-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Amit Shah <amit.shah@...hat.com>

commit 9ba5c80b1aea8648a3efe5f22dc1f7cacdfbeeb8 upstream.

When multiple ovq operations are being performed (lots of open/close
operations on virtio_console fds), the __send_control_msg() function can
get confused without locking.

A simple recipe to cause badness is:
* create a QEMU VM with two virtio-serial ports
* in the guest, do
  while true;do echo abc >/dev/vport0p1;done
  while true;do echo edf >/dev/vport0p2;done

In one run, this caused a panic in __send_control_msg().  In another, I
got

   virtio_console virtio0: control-o:id 0 is not a head!

This also results repeated messages similar to these on the host:

  qemu-kvm: virtio-serial-bus: Unexpected port id 478762112 for device virtio-serial-bus.0
  qemu-kvm: virtio-serial-bus: Unexpected port id 478762368 for device virtio-serial-bus.0

Reported-by: FuXiangChun <xfu@...hat.com>
Signed-off-by: Amit Shah <amit.shah@...hat.com>
Reviewed-by: Wanlong Gao <gaowanlong@...fujitsu.com>
Reviewed-by: Asias He <asias@...hat.com>
Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/char/virtio_console.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -132,6 +132,7 @@ struct ports_device {
 
 	/* To protect the vq operations for the control channel */
 	spinlock_t c_ivq_lock;
+	spinlock_t c_ovq_lock;
 
 	/* The current config space is stored here */
 	struct virtio_console_config config;
@@ -457,11 +458,14 @@ static ssize_t __send_control_msg(struct
 	vq = portdev->c_ovq;
 
 	sg_init_one(sg, &cpkt, sizeof(cpkt));
+
+	spin_lock(&portdev->c_ovq_lock);
 	if (virtqueue_add_buf(vq, sg, 1, 0, &cpkt) >= 0) {
 		virtqueue_kick(vq);
 		while (!virtqueue_get_buf(vq, &len))
 			cpu_relax();
 	}
+	spin_unlock(&portdev->c_ovq_lock);
 	return 0;
 }
 
@@ -1722,6 +1726,7 @@ static int __devinit virtcons_probe(stru
 		unsigned int nr_added_bufs;
 
 		spin_lock_init(&portdev->c_ivq_lock);
+		spin_lock_init(&portdev->c_ovq_lock);
 		INIT_WORK(&portdev->control_work, &control_work_handler);
 
 		nr_added_bufs = fill_queue(portdev->c_ivq,

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