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[Qemu-devel] [RFC] virtio-rng: add a watchdog
From: |
Laurent Vivier |
Subject: |
[Qemu-devel] [RFC] virtio-rng: add a watchdog |
Date: |
Tue, 11 Jun 2019 19:20:32 +0200 |
The virtio-rng linux driver can be stuck in virtio_read() on a
wait_for_completion_killable() call if the virtio-rng device in QEMU
doesn't provide data.
It's a problem, because virtio_read() is called from rng_get_data() with
reading_mutex() held. The same mutex is taken by add_early_randomness()
and hwrng_fillfn() and this brings to a hang during the boot sequence if
the virtio-rng driver is builtin.
Moreover, another lock is taken (rng_mutex) when the hwrng driver
wants to switch the RNG device or the user tries to unplug the virtio-rng
PCI card, and this can hang too because the virtio-rng driver is only able
to release the card if the virtio-rng device sends back the virtqueue element.
# echo -n virtio_rng.1 > /sys/class/misc/hw_random/rng_current
[ 240.165234] INFO: task kworker/u2:1:34 blocked for more than 120 seconds.
[ 240.165961] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables
this message.
[ 240.166708] kworker/u2:1 D ffffffffb86b85a8 0 34 2
0x00000000
[ 240.166714] Workqueue: kacpi_hotplug acpi_hotplug_work_fn
[ 240.166716] ffffa0e8f3c0b890 0000000000000046 ffffa0e8f3c00000
ffffa0e8f3c0bfd8
[ 240.166717] ffffa0e8f3c0bfd8 ffffa0e8f3c0bfd8 ffffa0e8f3c00000
ffffffffb86b85a0
[ 240.166719] ffffffffb86b85a4 ffffa0e8f3c00000 00000000ffffffff
ffffffffb86b85a8
[ 240.166720] Call Trace:
[ 240.166725] [<ffffffffb82a61c9>] schedule_preempt_disabled+0x29/0x70
[ 240.166727] [<ffffffffb82a40f7>] __mutex_lock_slowpath+0xc7/0x1d0
[ 240.166728] [<ffffffffb82a350f>] mutex_lock+0x1f/0x2f
[ 240.166730] [<ffffffffb8022b52>] hwrng_register+0x32/0x1d0
[ 240.166733] [<ffffffffc07fa149>] virtrng_scan+0x19/0x30 [virtio_rng]
[ 240.166744] [<ffffffffc03108db>] virtio_dev_probe+0x1eb/0x290 [virtio]
[ 240.166746] [<ffffffffb803d6e5>] driver_probe_device+0x145/0x3c0
...
In some case, the QEMU RNG backend is not able to provide data, and
the virtio-rng device is not aware of that:
- with rng-random using /dev/random and no entropy is available,
- with rng-egd started with a socket in "server,nowait" mode and
no daemon connected,
- with rng-egd and an egd daemon that is not providing enough data,
- ...
To release the locks regularly, this patch adds a watchdog in QEMU
virtio-rng device that sends back to the guest the virtqueue buffer
with a 0 byte payload. This case is expected and correctly managed by
the hwrng core.
Signed-off-by: Laurent Vivier <address@hidden>
---
hw/virtio/virtio-rng.c | 23 +++++++++++++++++++++++
include/hw/virtio/virtio-rng.h | 1 +
2 files changed, 24 insertions(+)
diff --git a/hw/virtio/virtio-rng.c b/hw/virtio/virtio-rng.c
index 30493a258622..173ecd370c0e 100644
--- a/hw/virtio/virtio-rng.c
+++ b/hw/virtio/virtio-rng.c
@@ -19,6 +19,8 @@
#include "qom/object_interfaces.h"
#include "trace.h"
+#define VIRTIO_RNG_WATCHDOG_MS 500
+
static bool is_guest_ready(VirtIORNG *vrng)
{
VirtIODevice *vdev = VIRTIO_DEVICE(vrng);
@@ -38,6 +40,21 @@ static size_t get_request_size(VirtQueue *vq, unsigned quota)
return in;
}
+static void watchdog(void *opaque)
+{
+ VirtIORNG *vrng = opaque;
+ VirtIODevice *vdev = VIRTIO_DEVICE(vrng);
+ VirtQueueElement *elem;
+
+ /* wake up driver */
+ elem = virtqueue_pop(vrng->vq, sizeof(VirtQueueElement));
+ if (!elem) {
+ return;
+ }
+ virtqueue_push(vrng->vq, elem, 0);
+ virtio_notify(vdev, vrng->vq);
+}
+
static void virtio_rng_process(VirtIORNG *vrng);
/* Send data from a char device over to the guest */
@@ -98,6 +115,9 @@ static void virtio_rng_process(VirtIORNG *vrng)
return;
}
+ timer_mod(vrng->watchdog_timer,
+ qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL) + VIRTIO_RNG_WATCHDOG_MS);
+
if (vrng->activate_timer) {
timer_mod(vrng->rate_limit_timer,
qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL) +
vrng->conf.period_ms);
@@ -222,6 +242,7 @@ static void virtio_rng_device_realize(DeviceState *dev,
Error **errp)
vrng->vq = virtio_add_queue(vdev, 8, handle_input);
vrng->quota_remaining = vrng->conf.max_bytes;
+ vrng->watchdog_timer = timer_new_ms(QEMU_CLOCK_VIRTUAL, watchdog, vrng);
vrng->rate_limit_timer = timer_new_ms(QEMU_CLOCK_VIRTUAL,
check_rate_limit, vrng);
vrng->activate_timer = true;
@@ -236,6 +257,8 @@ static void virtio_rng_device_unrealize(DeviceState *dev,
Error **errp)
VirtIORNG *vrng = VIRTIO_RNG(dev);
qemu_del_vm_change_state_handler(vrng->vmstate);
+ timer_del(vrng->watchdog_timer);
+ timer_free(vrng->watchdog_timer);
timer_del(vrng->rate_limit_timer);
timer_free(vrng->rate_limit_timer);
virtio_cleanup(vdev);
diff --git a/include/hw/virtio/virtio-rng.h b/include/hw/virtio/virtio-rng.h
index 922dce7caccf..05d6b0e7d881 100644
--- a/include/hw/virtio/virtio-rng.h
+++ b/include/hw/virtio/virtio-rng.h
@@ -42,6 +42,7 @@ typedef struct VirtIORNG {
/* We purposefully don't migrate this state. The quota will reset on the
* destination as a result. Rate limiting is host state, not guest state.
*/
+ QEMUTimer *watchdog_timer;
QEMUTimer *rate_limit_timer;
int64_t quota_remaining;
bool activate_timer;
--
2.21.0
- [Qemu-devel] [RFC] virtio-rng: add a watchdog,
Laurent Vivier <=