linux-kernel - Re: [PATCH 3/4] xen/manage: Guard against user-space initiated poweroff and XenBus.

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Message-ID: <533ABC8A.5080405@citrix.com>
Date:	Tue, 1 Apr 2014 14:18:02 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	<Ian.Campbell@...rix.com>, <xen-devel@...ts.xenproject.org>,
	<linux-kernel@...r.kernel.org>, <JBeulich@...e.com>,
	<boris.ostrovsky@...cle.com>
Subject: Re: [PATCH 3/4] xen/manage: Guard against user-space initiated poweroff
 and XenBus.

On 08/11/13 17:38, Konrad Rzeszutek Wilk wrote:
> There is a race case where the user does 'poweroff'
> and at the same time the system admin does 'xl shutdown'.
> 
> Depending on the race, the system_state will be SYSTEM_RUNNING or
> SYSTEM_POWER_OFF. If SYSTEM_RUNNING we just end up making
> a duplicate call to 'poweroff' (while it is running).
> 
> That will fail or execute (And if executed then it will be
> stuck in the reboot_mutex mutex). But nobody will care b/c the
> machine is in poweroff sequence.

If this race isn't a problem...

> If the system_state is SYSTEM_POWER_OFF then we end up making
> a duplicate call to kernel_power_off. There is no locking
> there so we walk in the same steps as what 'poweroff'
> has been doing.

... and this one doesn't happen because do_power_off() calls
orderly_poweroff(false) so does not call kernel_power_off().

Then isn't the patch unnecessary?

David
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