[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH v2 1/1] virtio-blk: fix race on guest notifiers
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH v2 1/1] virtio-blk: fix race on guest notifiers |
Date: |
Fri, 10 Mar 2017 17:47:52 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 |
On 07/03/2017 14:16, Halil Pasic wrote:
> The commits 03de2f527 "virtio-blk: do not use vring in dataplane" and
> 9ffe337c08 "virtio-blk: always use dataplane path if ioeventfd is active"
> changed how notifications are done for virtio-blk substantially. Due to a
> race condition, interrupts are lost when irqfd behind the guest notifier
> is torn down after notify_guest_bh was scheduled but before it actually
> runs.
>
> Let's fix this by forcing guest notifications before cleaning up the
> irqfd's. Let's also add some explanatory comments.
>
> Cc: address@hidden
> Signed-off-by: Halil Pasic <address@hidden>
> Reported-by: Michael A. Tebolt <address@hidden>
> Tested-by: Michael A. Tebolt <address@hidden>
> Suggested-by: Paolo Bonzini <address@hidden>
> ---
>
> This patch withstood the test case which discovered the problem
> for several days (as reported by Michale Tebolt).
>
> v1 --> v2:
> * Fixed typo pointed out by Connie
> * Added Tested-by
Hi Halil,
I found a similar issue in NBD. Can you check if this patch fixes
the virtio-blk issue too?
Thanks,
Paolo
------ 8< ------------
diff --git a/block.c b/block.c
index f293ccb..e159251 100644
--- a/block.c
+++ b/block.c
@@ -4272,8 +4272,15 @@ void bdrv_attach_aio_context(BlockDriverState *bs,
void bdrv_set_aio_context(BlockDriverState *bs, AioContext *new_context)
{
+ AioContext *ctx;
+
bdrv_drain(bs); /* ensure there are no in-flight requests */
+ ctx = bdrv_get_aio_context(bs);
+ while (aio_poll(ctx, false)) {
+ /* wait for all bottom halves to execute */
+ }
+
bdrv_detach_aio_context(bs);
/* This function executes in the old AioContext so acquire the new one in
> ---
> hw/block/dataplane/virtio-blk.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
> index 5556f0e..045a580 100644
> --- a/hw/block/dataplane/virtio-blk.c
> +++ b/hw/block/dataplane/virtio-blk.c
> @@ -258,9 +258,16 @@ void virtio_blk_data_plane_stop(VirtIODevice *vdev)
> virtio_queue_aio_set_host_notifier_handler(vq, s->ctx, NULL);
> }
>
> - /* Drain and switch bs back to the QEMU main loop */
> + /* Drain and switch bs back to the QEMU main loop. After drain, the
> + * device will not submit (nor complete) any requests until dataplane
> + * starts again.
> + */
> blk_set_aio_context(s->conf->conf.blk, qemu_get_aio_context());
>
> + /* Notify guest before the guest notifiers get cleaned up */
> + qemu_bh_cancel(s->bh);
> + notify_guest_bh(s);
> +
> aio_context_release(s->ctx);
>
> for (i = 0; i < nvqs; i++) {
>