linux-kernel - Re: [tip:x86/asm] sched/x86_64: Don't save flags on context switch

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Message-ID: <CALCETrWoqu=7=-JYgZzcOcPsvYkA0eFTpbpmDUNA5=CLT3ykSw@mail.gmail.com>
Date:	Mon, 3 Nov 2014 15:02:43 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Jan Beulich <jbeulich@...e.com>, Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Sebastian Lackner <sebastian@...-team.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Chuck Ebbert <cebbert.lkml@...il.com>,
	Anish Bhatt <anish@...lsio.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:x86/asm] sched/x86_64: Don't save flags on context switch

On Mon, Nov 3, 2014 at 2:57 PM, Oleg Nesterov <oleg@...hat.com> wrote:
> Argh, sorry for confusion...
>
> On 11/03, Andy Lutomirski wrote:
>>
>> On Mon, Nov 3, 2014 at 1:58 PM, Oleg Nesterov <oleg@...hat.com> wrote:
>> > On 11/03, Oleg Nesterov wrote:
>> >>
>> > Btw, why retint_kernel() checks "interrupts on" ? It seems to me that
>> > that "interrupts off" is not possible, no? And this will be more clear
>> > when we remove the "exit_intr" label.
>>
>> We might get there from #MC or from any of a number of synchronous
>> errors (#GP from xyz_safe, #PF from some atomic uaccess thing or a
>> vmap fault, etc), and all of those have interrupts off.
>
> Yes, yes, exactly.
>
> I actually tried to say that irqs should be always disabled (afaics!).
> IOW "interrupts on" should not be possible, not "interrupts off".

But this is checking whether interrupts were on in the frame we're
returning to, not whether they're on right now, right?

--Andy
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