Re: [Xen-devel] [PATCH 4/4] xen/xenbus: Avoid synchronous wait on XenBus stalling shutdown/restart.

[David Vrabel <david.vrabel@citrix.com>]

On 31/03/14 21:33, Konrad Rzeszutek Wilk wrote:
> 
> Subject: [PATCH] xen/xenbus: Avoid synchronous wait on XenBus stalling
>  shutdown/restart.
> 
> The 'read_reply' works with 'process_msg' to read of a reply in XenBus.
> 'process_msg' is running from within the 'xenbus' thread. Whenever
> a message shows up in XenBus it is put on a xs_state.reply_list list
> and 'read_reply' picks it up.
> 
> The problem is if the backend domain or the xenstored process is killed.
> In which case 'xenbus' is still awaiting - and 'read_reply' if called -
> stuck forever waiting for the reply_list to have some contents.
> 
> This is normally not a problem - as the backend domain can come back
> or the xenstored process can be restarted. However if the domain
> is in process of being powered off/restarted/halted - there is no
> point of waiting on it coming back - as we are effectively being
> terminated and should not impede the progress.
> 
> This patch solves this problem by checking whether the guest is
> the right domain. If it is an initial domain and hurtling towards
> death - there is no point of continuing the wait. All other type
> of guests continue with their behavior.
> mechanism a bit more asynchronous.

Reviewed-by: David Vrabel <david.vrabel@citrix.com>

David