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Re: [RFC PATCH v1 18/25] hw/xen: Avoid crash when backend watch fires to


From: Paul Durrant
Subject: Re: [RFC PATCH v1 18/25] hw/xen: Avoid crash when backend watch fires too early
Date: Tue, 7 Mar 2023 15:43:17 +0000
User-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0

On 02/03/2023 15:34, David Woodhouse wrote:
From: Paul Durrant <pdurrant@amazon.com>

The xen-block code ends up calling aio_poll() through blkconf_geometry(),
which means we see watch events during the indirect call to
xendev_class->realize() in xen_device_realize(). Unfortunately this call
is made before populating the initial frontend and backend device nodes
in xenstore and hence xen_block_frontend_changed() (which is called from
a watch event) fails to read the frontend's 'state' node, and hence
believes the device is being torn down. This in-turn sets the backend
state to XenbusStateClosed and causes the device to be deleted before it
is fully set up, leading to the crash.
By simply moving the call to xendev_class->realize() after the initial
xenstore nodes are populated, this sorry state of affairs is avoided.

Reported-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
  hw/xen/xen-bus.c | 14 +++++++-------
  1 file changed, 7 insertions(+), 7 deletions(-)


Reviewed-by: Paul Durrant <paul@xen.org>




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