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From: "Michael S. Tsirkin" <mst@redhat.com>
To: Laurent Vivier <lvivier@redhat.com>
Cc: "Amit Shah" <amit@kernel.org>, "Jason Wang" <jasowang@redhat.com>,
	qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org,
	"Philippe Mathieu-Daudé" <philmd@redhat.com>,
	"Martin Wilck" <mwilck@suse.com>
Subject: Re: [PATCH v2] virtio-rng: return available data with O_NONBLOCK
Date: Tue, 11 Aug 2020 09:14:09 -0400	[thread overview]
Message-ID: <20200811090814-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <085f699b-e391-7363-b63e-3b11cc04e50d@redhat.com>

On Tue, Aug 11, 2020 at 03:00:14PM +0200, Laurent Vivier wrote:
> No problem. This code is tricky and it took me several months to really
> start to understand it ...

Oh great, we actually have someone who understands the code!
Maybe you can help me understand: virtio_read
takes the buf pointer and puts it in the vq.
It can then return to caller (e.g. on a signal).
Device can meanwhile write into the buffer.

It looks like if another call then happens, and that
other call uses a different buffer, virtio rng
will happily return the data written into the
original buf pointer, confusing the caller.

Is that right?

-- 
MST



WARNING: multiple messages have this Message-ID (diff)
From: "Michael S. Tsirkin" <mst@redhat.com>
To: Laurent Vivier <lvivier@redhat.com>
Cc: "Amit Shah" <amit@kernel.org>,
	qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org,
	"Philippe Mathieu-Daudé" <philmd@redhat.com>,
	"Martin Wilck" <mwilck@suse.com>
Subject: Re: [PATCH v2] virtio-rng: return available data with O_NONBLOCK
Date: Tue, 11 Aug 2020 09:14:09 -0400	[thread overview]
Message-ID: <20200811090814-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <085f699b-e391-7363-b63e-3b11cc04e50d@redhat.com>

On Tue, Aug 11, 2020 at 03:00:14PM +0200, Laurent Vivier wrote:
> No problem. This code is tricky and it took me several months to really
> start to understand it ...

Oh great, we actually have someone who understands the code!
Maybe you can help me understand: virtio_read
takes the buf pointer and puts it in the vq.
It can then return to caller (e.g. on a signal).
Device can meanwhile write into the buffer.

It looks like if another call then happens, and that
other call uses a different buffer, virtio rng
will happily return the data written into the
original buf pointer, confusing the caller.

Is that right?

-- 
MST

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Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization

  reply	other threads:[~2020-08-11 13:14 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-15 13:32 [PATCH v2] virtio-rng: return available data with O_NONBLOCK mwilck
2020-08-11 10:23 ` Reminder: " Martin Wilck
2020-08-11 10:37 ` Philippe Mathieu-Daudé
2020-08-11 12:02   ` Laurent Vivier
2020-08-11 12:02     ` Laurent Vivier
2020-08-11 12:22     ` Martin Wilck
2020-08-11 12:39       ` Laurent Vivier
2020-08-11 12:39         ` Laurent Vivier
2020-08-11 12:53         ` Martin Wilck
2020-08-11 13:00           ` Laurent Vivier
2020-08-11 13:00             ` Laurent Vivier
2020-08-11 13:14             ` Michael S. Tsirkin [this message]
2020-08-11 13:14               ` Michael S. Tsirkin
2020-08-11 13:53               ` Laurent Vivier
2020-08-11 13:53                 ` Laurent Vivier
2020-08-11 14:49                 ` Michael S. Tsirkin
2020-08-11 14:49                   ` Michael S. Tsirkin
2020-08-11 15:00                   ` Laurent Vivier
2020-08-11 15:00                     ` Laurent Vivier
2020-08-11 14:12           ` Martin Wilck
2020-08-11 11:26 ` Michael S. Tsirkin
2020-08-11 11:26   ` Michael S. Tsirkin
2020-08-11 12:07   ` Martin Wilck
2020-08-11 12:58     ` Michael S. Tsirkin
2020-08-11 12:58       ` Michael S. Tsirkin

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