linux-kernel - Re: [PATCHv1] x86: don't schedule when handling #NM exception

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Message-ID: <531DF319.6010800@citrix.com>
Date:	Mon, 10 Mar 2014 17:15:05 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	<linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Ingo Molnar" <mingo@...hat.com>, <xen-devel@...ts.xen.org>,
	Sarah Newman <srn@...mr.com>
Subject: Re: [PATCHv1] x86: don't schedule when handling #NM exception

On 10/03/14 16:40, H. Peter Anvin wrote:
> On 03/10/2014 09:17 AM, David Vrabel wrote:
>> math_state_restore() is called from the #NM exception handler.  It may
>> do a GFP_KERNEL allocation (in init_fpu()) which may schedule.
>>
>> Change this allocation to GFP_ATOMIC, but leave all the other callers
>> of init_fpu() or fpu_alloc() using GFP_KERNEL.
> 
> And what the [Finnish] do you do if GFP_ATOMIC fails?

The same thing it used to do -- kill the task with SIGKILL.  I haven't
changed this behaviour.

> Sarah's patchset switches Xen PV to use eagerfpu unconditionally, which
> removes the dependency on #NM and is the right thing to do.

Ok. I'll wait for this series and not pursue this patch any further.

David
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