From: Stefan Hajnoczi <stefanha@redhat.com>
To: qemu-devel@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>,
Peter Maydell <peter.maydell@linaro.org>,
Sergio Lopez <slp@redhat.com>,
qemu-block@nongnu.org, "Michael S. Tsirkin" <mst@redhat.com>,
Max Reitz <mreitz@redhat.com>,
Stefan Hajnoczi <stefanha@redhat.com>
Subject: [PULL 2/2] virtio-blk: schedule virtio_notify_config to run on main context
Date: Wed, 25 Sep 2019 18:44:00 +0100 [thread overview]
Message-ID: <20190925174400.8578-3-stefanha@redhat.com> (raw)
In-Reply-To: <20190925174400.8578-1-stefanha@redhat.com>
From: Sergio Lopez <slp@redhat.com>
virtio_notify_config() needs to acquire the global mutex, which isn't
allowed from an iothread, and may lead to a deadlock like this:
- main thead
* Has acquired: qemu_global_mutex.
* Is trying the acquire: iothread AioContext lock via
AIO_WAIT_WHILE (after aio_poll).
- iothread
* Has acquired: AioContext lock.
* Is trying to acquire: qemu_global_mutex (via
virtio_notify_config->prepare_mmio_access).
If virtio_blk_resize() is called from an iothread, schedule
virtio_notify_config() to be run in the main context BH.
[Removed unnecessary newline as suggested by Kevin Wolf
<kwolf@redhat.com>.
--Stefan]
Signed-off-by: Sergio Lopez <slp@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-id: 20190916112411.21636-1-slp@redhat.com
Message-Id: <20190916112411.21636-1-slp@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
hw/block/virtio-blk.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index 18851601cb..ed2ddebd2b 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -16,6 +16,7 @@
#include "qemu/iov.h"
#include "qemu/module.h"
#include "qemu/error-report.h"
+#include "qemu/main-loop.h"
#include "trace.h"
#include "hw/block/block.h"
#include "hw/qdev-properties.h"
@@ -1086,11 +1087,24 @@ static int virtio_blk_load_device(VirtIODevice *vdev, QEMUFile *f,
return 0;
}
+static void virtio_resize_cb(void *opaque)
+{
+ VirtIODevice *vdev = opaque;
+
+ assert(qemu_get_current_aio_context() == qemu_get_aio_context());
+ virtio_notify_config(vdev);
+}
+
static void virtio_blk_resize(void *opaque)
{
VirtIODevice *vdev = VIRTIO_DEVICE(opaque);
- virtio_notify_config(vdev);
+ /*
+ * virtio_notify_config() needs to acquire the global mutex,
+ * so it can't be called from an iothread. Instead, schedule
+ * it to be run in the main context BH.
+ */
+ aio_bh_schedule_oneshot(qemu_get_aio_context(), virtio_resize_cb, vdev);
}
static const BlockDevOps virtio_block_ops = {
--
2.21.0
next prev parent reply other threads:[~2019-09-25 17:47 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-25 17:43 [PULL 0/2] Block patches Stefan Hajnoczi
2019-09-25 17:43 ` [PULL 1/2] util/ioc.c: try to reassure Coverity about qemu_iovec_init_extended Stefan Hajnoczi
2019-09-26 10:54 ` Vladimir Sementsov-Ogievskiy
2019-09-25 17:44 ` Stefan Hajnoczi [this message]
2019-09-26 6:16 ` [PULL 0/2] Block patches no-reply
2019-09-26 12:06 ` Vladimir Sementsov-Ogievskiy
2019-09-26 12:56 ` Peter Maydell
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