| Message ID | 20140908152951.GA28459@zen.redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, Sep 08, 2014 at 11:29:51PM +0800, Amos Kong wrote: > On Wed, Aug 06, 2014 at 01:55:29PM +0530, Amit Shah wrote: > > On (Wed) 06 Aug 2014 [16:05:41], Amos Kong wrote: > > > On Wed, Aug 06, 2014 at 01:35:15AM +0800, Amos Kong wrote: > > > > When we try to hot-remove a busy virtio-rng device from QEMU monitor, > > > > the device can't be hot-removed. Because virtio-rng driver hangs at > > > > wait_for_completion_killable(). > > > > > > > > This patch fixed the hang by completing have_data completion before > > > > unregistering a virtio-rng device. > > > > > > Hi Amit, > > > > > > Before applying this patch, it's blocking insider wait_for_completion_killable() > > > Applied this patch, wait_for_completion_killable() returns 0, > > > and vi->data_avail becomes 0, then rng_get_date() will return 0. > > > > Thanks for checking this. > > > > > Is it expected result? > > Hi Amit > > I think what will happen is vi->data_avail will be set to whatever it > > was set last. In case of a previous successful read request, the > > data_avail will be set to whatever number of bytes the host gave. On > > doing a hot-unplug on the succeeding wait, the value in data_avail > > will be re-used, and the hwrng core will wrongly take some bytes in > > the buffer as input from the host. > > > > So, I think we need to set vi->data_avail = 0; before calling > > wait_event_completion_killable(). I finally understand content, we need to set vi->data_avail to 0 before returning virtio_read(), it might enter wait_event_completion_killable() when we try to remove the device. We call complete() in remove_common(), then wait_event_completion_killable() will exit, but virtio_read() will be re-entered if the device still isn't unregistered, then re-stuck inside wait_event_completion_killable(). I tested some complex condition (both quick/slow backend), I found some problem in below two patches. I will post another fix later. The test result is expected. 1. Hotplug remove virtio-rng0, dd process will exit with an error: "dd: error reading ‘/dev/hwrng’: Operation not permitted" virtio-rng0 disappear from 'info pci' 2. Re-read by dd, hotplug virtio-rng1, dd process exit with same error, virtio-rng1 disappear Thanks, Amos > > > > Amit > > In my latest debugging, I found the hang is caused by unexpected reading > when we started to remove the device. > > I have two draft fix, 1) is skip unexpected reading by checking a > remove flag. 2) is unregistering device at the beginning of > remove_common(). I think second patch is better if it won't cause > new problem. > > The original patch (complete in remove_common()) is still necessary. > > Test results: hotplug issue disappeared (dd process will quit). > > > diff --git a/drivers/char/hw_random/virtio-rng.c > b/drivers/char/hw_random/virtio-rng.c > index 2e3139e..028797c 100644 > --- a/drivers/char/hw_random/virtio-rng.c > +++ b/drivers/char/hw_random/virtio-rng.c > @@ -35,6 +35,7 @@ struct virtrng_info { > unsigned int data_avail; > int index; > bool busy; > + bool remove; > bool hwrng_register_done; > }; > > @@ -68,6 +69,9 @@ static int virtio_read(struct hwrng *rng, void *buf, > size_t size, bool wait) > int ret; > struct virtrng_info *vi = (struct virtrng_info *)rng->priv; > > + if (vi->remove) > + return 0; > + > if (!vi->busy) { > vi->busy = true; > init_completion(&vi->have_data); > @@ -137,6 +141,8 @@ static void remove_common(struct virtio_device > *vdev) > { > struct virtrng_info *vi = vdev->priv; > > + vi->remove = true; > + complete(&vi->have_data); > vdev->config->reset(vdev); > vi->busy = false; > if (vi->hwrng_register_done) > > > diff --git a/drivers/char/hw_random/virtio-rng.c > b/drivers/char/hw_random/virtio-rng.c > index 2e3139e..9b8c2ce 100644 > --- a/drivers/char/hw_random/virtio-rng.c > +++ b/drivers/char/hw_random/virtio-rng.c > @@ -137,10 +137,11 @@ static void remove_common(struct virtio_device > *vdev) > { > struct virtrng_info *vi = vdev->priv; > > - vdev->config->reset(vdev); > - vi->busy = false; > if (vi->hwrng_register_done) > hwrng_unregister(&vi->hwrng); > + complete(&vi->have_data); > + vdev->config->reset(vdev); > + vi->busy = false; > vdev->config->del_vqs(vdev); > ida_simple_remove(&rng_index_ida, vi->index); > kfree(vi); -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c index 2e3139e..028797c 100644 --- a/drivers/char/hw_random/virtio-rng.c +++ b/drivers/char/hw_random/virtio-rng.c @@ -35,6 +35,7 @@ struct virtrng_info { unsigned int data_avail; int index; bool busy; + bool remove; bool hwrng_register_done; }; @@ -68,6 +69,9 @@ static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait) int ret; struct virtrng_info *vi = (struct virtrng_info *)rng->priv; + if (vi->remove) + return 0; + if (!vi->busy) { vi->busy = true; init_completion(&vi->have_data); @@ -137,6 +141,8 @@ static void remove_common(struct virtio_device *vdev) { struct virtrng_info *vi = vdev->priv; + vi->remove = true; + complete(&vi->have_data); vdev->config->reset(vdev); vi->busy = false; if (vi->hwrng_register_done) diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c index 2e3139e..9b8c2ce 100644 --- a/drivers/char/hw_random/virtio-rng.c +++ b/drivers/char/hw_random/virtio-rng.c @@ -137,10 +137,11 @@ static void remove_common(struct virtio_device *vdev) { struct virtrng_info *vi = vdev->priv; - vdev->config->reset(vdev); - vi->busy = false; if (vi->hwrng_register_done) hwrng_unregister(&vi->hwrng); + complete(&vi->have_data); + vdev->config->reset(vdev); + vi->busy = false; vdev->config->del_vqs(vdev); ida_simple_remove(&rng_index_ida, vi->index);