linux-kernel - Re: [PATCH v2] um: read multiple msg from virtio slave request fd

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Date:   Tue, 09 Aug 2022 20:07:47 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     Benjamin Beichler <benjamin.beichler@...-rostock.de>,
        Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>
Cc:     linux-um@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] um: read multiple msg from virtio slave request fd

On Tue, 2022-06-07 at 11:27 +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.
> 
> Anyways, in general it seems to be more natural to consume always all
> messages from a socket, instead of only a single one.
> 
> Fixes: 2cd097ba8c05 ("um: virtio: Implement VHOST_USER_PROTOCOL_F_SLAVE_REQ")
> Signed-off-by: Benjamin Beichler <benjamin.beichler@...-rostock.de>
> 

Reviewed-by: Johannes Berg <johannes@...solutions.net>


Sorry, should've sent that earlier.

johannes