Hello,
My static analysis tool reports two possible deadlocks in the vhost
driver in Linux 5.16:
#BUG 1
vhost_net_set_backend()
mutex_lock(&n->dev.mutex); --> Line 1511(Lock A)
vhost_net_ubuf_put_wait_and_free()
vhost_net_ubuf_put_and_wait()
wait_event(ubufs->wait ...); --> Line 260 (Wait X)
vhost_net_ioctl()
mutex_lock(&n->dev.mutex); --> Line 1734 (Lock A)
vhost_net_flush()
vhost_net_ubuf_put_and_wait()
vhost_net_ubuf_put()
wake_up(&ubufs->wait); --> Line 253 (Wake X)
When vhost_net_set_backend() is executed, "Wait X" is performed by
holding "Lock A". If vhost_net_ioctl() is executed at this time, "Wake
X" cannot be performed to wake up "Wait X" in vhost_net_set_backend(),
because "Lock A" has been already hold by vhost_net_set_backend(),
causing a possible deadlock.
#BUG2
vhost_net_set_backend()
mutex_lock(&vq->mutex); --> Line 1522(Lock A)
vhost_net_ubuf_put_wait_and_free()
vhost_net_ubuf_put_and_wait()
wait_event(ubufs->wait ...); --> Line 260 (Wait X)
handle_tx()
mutex_lock_nested(&vq->mutex, ...); --> Line 966 (Lock A)
handle_tx_zerocopy()
vhost_net_ubuf_put()
wake_up(&ubufs->wait); --> Line 253 (Wake X)
When vhost_net_set_backend() is executed, "Wait X" is performed by
holding "Lock A". If handle_tx() is executed at this time, "Wake X"
cannot be performed to wake up "Wait X" in vhost_net_set_backend(),
because "Lock A" has been already hold by vhost_net_set_backend(),
causing a possible deadlock.
I am not quite sure whether these possible problems are real and how to
fix them if they are real.
Any feedback would be appreciated, thanks :)
Best wishes,
Jia-Ju Bai
