Messages in this thread Patch in this message | | | Subject | Re: [PATCH] um: read multiple msg from virtio slave request fd | From | Johannes Berg <> | Date | Wed, 01 Jun 2022 19:13:29 +0200 |
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On Wed, 2022-06-01 at 15:37 +0000, Benjamin Beichler wrote: > If VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS is activated, the user mode > linux virtio irq handler only read one msg from the corresponding socket. > This creates issues, when the device emulation creates multiple call > requests (e.g. for multiple virtqueues), as the socket buffer tend to fill > up and the call requests are delayed. > > This creates a deadlock situation, when the device simulation blocks, > because of sending a msg and the kernel side blocks because of > synchronously waiting for an acknowledge of kick request. > > Actually inband notifications are meant to be used in combination with the > time travel protocol, but it is not required, therefore this corner case > needs to be handled.
Hmm. How did you run into this? Why would a device send many messages and not wait for ACK, but the kernel side actually waits for ACK? What would the use case for that be? Seems a bit odd, if both wait for ACK there shouldn't be an issue?
Anyway, I guess I don't mind fixing this regardless of whether I see a use case where it could happen :-)
> +++ b/arch/um/drivers/virtio_uml.c > @@ -363,45 +363,47 @@ static irqreturn_t vu_req_read_message(struct virtio_uml_device *vu_dev, > struct vhost_user_msg msg; > u8 extra_payload[512]; > } msg; > - int rc; > - > - rc = vhost_user_recv_req(vu_dev, &msg.msg, > - sizeof(msg.msg.payload) + > - sizeof(msg.extra_payload)); > - > - if (rc)
This code changed a bit, you should rebase onto the uml tree's for-next branch.
> + while (1) { > + if (vhost_user_recv_req(vu_dev, &msg.msg, > + sizeof(msg.msg.payload) > + + sizeof(msg.extra_payload)))
prefer to keep the + on the previous line.
That said, my attempt at rebasing this made it all fail completely, maybe you have better luck :)
johannes
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