[net,1/2] vhost: use mutex_lock_nested() in vhost_dev_lock_vqs()
diff mbox series

Message ID 1516699646-7321-1-git-send-email-jasowang@redhat.com
State New, archived
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Series
  • [net,1/2] vhost: use mutex_lock_nested() in vhost_dev_lock_vqs()
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Commit Message

Jason Wang Jan. 23, 2018, 9:27 a.m. UTC
We used to call mutex_lock() in vhost_dev_lock_vqs() which tries to
hold mutexes of all virtqueues. This may confuse lockdep to report a
possible deadlock because of trying to hold locks belong to same
class. Switch to use mutex_lock_nested() to avoid false positive.

Fixes: 6b1e6cc7855b0 ("vhost: new device IOTLB API")
Reported-by: syzbot+dbb7c1161485e61b0241@syzkaller.appspotmail.com
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 drivers/vhost/vhost.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Michael S. Tsirkin Jan. 23, 2018, 3:57 p.m. UTC | #1
On Tue, Jan 23, 2018 at 05:27:25PM +0800, Jason Wang wrote:
> We used to call mutex_lock() in vhost_dev_lock_vqs() which tries to
> hold mutexes of all virtqueues. This may confuse lockdep to report a
> possible deadlock because of trying to hold locks belong to same
> class. Switch to use mutex_lock_nested() to avoid false positive.
> 
> Fixes: 6b1e6cc7855b0 ("vhost: new device IOTLB API")
> Reported-by: syzbot+dbb7c1161485e61b0241@syzkaller.appspotmail.com
> Signed-off-by: Jason Wang <jasowang@redhat.com>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

> ---
>  drivers/vhost/vhost.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 33ac2b1..549771a 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -904,7 +904,7 @@ static void vhost_dev_lock_vqs(struct vhost_dev *d)
>  {
>  	int i = 0;
>  	for (i = 0; i < d->nvqs; ++i)
> -		mutex_lock(&d->vqs[i]->mutex);
> +		mutex_lock_nested(&d->vqs[i]->mutex, i);
>  }
>  
>  static void vhost_dev_unlock_vqs(struct vhost_dev *d)
> -- 
> 2.7.4
David Miller Jan. 24, 2018, 9:38 p.m. UTC | #2
From: Jason Wang <jasowang@redhat.com>
Date: Tue, 23 Jan 2018 17:27:25 +0800

> We used to call mutex_lock() in vhost_dev_lock_vqs() which tries to
> hold mutexes of all virtqueues. This may confuse lockdep to report a
> possible deadlock because of trying to hold locks belong to same
> class. Switch to use mutex_lock_nested() to avoid false positive.
> 
> Fixes: 6b1e6cc7855b0 ("vhost: new device IOTLB API")
> Reported-by: syzbot+dbb7c1161485e61b0241@syzkaller.appspotmail.com
> Signed-off-by: Jason Wang <jasowang@redhat.com>

Michael, I see you ACK'd this, meaning that you're OK with these two
fixes going via my net tree?

Thanks.
Michael S. Tsirkin Jan. 24, 2018, 9:46 p.m. UTC | #3
On Wed, Jan 24, 2018 at 04:38:30PM -0500, David Miller wrote:
> From: Jason Wang <jasowang@redhat.com>
> Date: Tue, 23 Jan 2018 17:27:25 +0800
> 
> > We used to call mutex_lock() in vhost_dev_lock_vqs() which tries to
> > hold mutexes of all virtqueues. This may confuse lockdep to report a
> > possible deadlock because of trying to hold locks belong to same
> > class. Switch to use mutex_lock_nested() to avoid false positive.
> > 
> > Fixes: 6b1e6cc7855b0 ("vhost: new device IOTLB API")
> > Reported-by: syzbot+dbb7c1161485e61b0241@syzkaller.appspotmail.com
> > Signed-off-by: Jason Wang <jasowang@redhat.com>
> 
> Michael, I see you ACK'd this, meaning that you're OK with these two
> fixes going via my net tree?
> 
> Thanks.

Yes - this seems to be what Jason wanted (judging by the net
tag in the subject) and I'm fine with it.
Thanks a lot.
David Miller Jan. 24, 2018, 9:55 p.m. UTC | #4
From: "Michael S. Tsirkin" <mst@redhat.com>
Date: Wed, 24 Jan 2018 23:46:19 +0200

> On Wed, Jan 24, 2018 at 04:38:30PM -0500, David Miller wrote:
>> From: Jason Wang <jasowang@redhat.com>
>> Date: Tue, 23 Jan 2018 17:27:25 +0800
>> 
>> > We used to call mutex_lock() in vhost_dev_lock_vqs() which tries to
>> > hold mutexes of all virtqueues. This may confuse lockdep to report a
>> > possible deadlock because of trying to hold locks belong to same
>> > class. Switch to use mutex_lock_nested() to avoid false positive.
>> > 
>> > Fixes: 6b1e6cc7855b0 ("vhost: new device IOTLB API")
>> > Reported-by: syzbot+dbb7c1161485e61b0241@syzkaller.appspotmail.com
>> > Signed-off-by: Jason Wang <jasowang@redhat.com>
>> 
>> Michael, I see you ACK'd this, meaning that you're OK with these two
>> fixes going via my net tree?
>> 
>> Thanks.
> 
> Yes - this seems to be what Jason wanted (judging by the net
> tag in the subject) and I'm fine with it.
> Thanks a lot.

Great, not a problem, done.

Patch
diff mbox series

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 33ac2b1..549771a 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -904,7 +904,7 @@  static void vhost_dev_lock_vqs(struct vhost_dev *d)
 {
 	int i = 0;
 	for (i = 0; i < d->nvqs; ++i)
-		mutex_lock(&d->vqs[i]->mutex);
+		mutex_lock_nested(&d->vqs[i]->mutex, i);
 }
 
 static void vhost_dev_unlock_vqs(struct vhost_dev *d)