[PATCH 3.4 53/88] virtio: console: add locking around c_ovq operations

Greg Kroah-Hartman
2014-06-10T00:25:03Z

From: Amit Shah <amit.shah@redhat.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@redhat.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Reviewed-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>
Reviewed-by: Asias He <asias@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
[wyj: Backported to 3.4: adjust context]
Signed-off-by: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
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;
@@ -460,11 +461,14 @@ 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, GFP_ATOMIC) >= 0) {
virtqueue_kick(vq);
while (!virtqueue_get_buf(vq, &len))
cpu_relax();
}
+ spin_unlock(&portdev->c_ovq_lock);
return 0;
}

@@ -1752,6 +1756,7 @@ 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,