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

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Message-ID: <20140401140319.GA8207@phenom.dumpdata.com>
Date:	Tue, 1 Apr 2014 10:03:19 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	David Vrabel <david.vrabel@...rix.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 Tue, Apr 01, 2014 at 02:18:02PM +0100, David Vrabel wrote:
> 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?

Yup :-)

I realized that once I wrote up the race condition.
> 
> David
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