linux-kernel - Re: [rfc-patch, bugfix] x86-microcode

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Date:	Mon, 4 Aug 2008 22:01:23 +0200
From:	"Dmitry Adamushko" <dmitry.adamushko@...il.com>
To:	"Max Krasnyansky" <maxk@...lcomm.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Tigran Aivazian" <tigran@...azian.fsnet.co.uk>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Peter Oruba" <peter.oruba@....com>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [rfc-patch, bugfix] x86-microcode

2008/8/4 Max Krasnyansky <maxk@...lcomm.com>:
> Dmitry Adamushko wrote:
>> Hi,
>>
>>
>> [ consider it a pre-release and RFC... I'm a bit in hurry now and just send what I have got by this moment.
>> Although, I expect it to be workable ]
>>
>>
>> this change is supposed to fix bug#11197 (note, its name "Oops in microcode sysfs registration" is misleading)
>>
>> The problem description can be found here:
>> http://www.ussg.iu.edu/hypermail/linux/kernel/0807.3/3791.html
>> or
>> http://lkml.org/lkml/2008/7/24/260
>>
>> perhaps it does look quite bulky for -rc, although it's mainly move-redesign-some-bits of the code and
>> I tried to preserve the original logic (even if it looked like a possible optimizations might had been applied)
>> as much as possible.
>>
>> The basic idea is that we introduce another mechanism to run ucode-updates on a target cpu
>> and replace set_cpus_allowed_ptr() in (1) cpu-hotplug events and (2) module load.
>>
>>
>> [1/2] x86-microcode: generic updates
>>
>> Basically, it introduces microcode_update_cpu() which can be run either from start_secondary()
>> (perhaps via a function pointer) or scheduled via keventd ([2/2]) and reworks the logic of cpu-hotplug events.
>>
>> [2/2] x86-microcode: do updates via workqueue
>
> Looks good to me. You did not change the old interface which still does
> set_cpus_allowed_ptr() (ie racy against sched_setaffinity())

ah, right. I've only fixed reload_store() vs. cpu_down().

sched_setaffinity() calls get_online_cpus() so a pair of
cpu_maps_update_begin() + cpu_hotplug_begin() would need to be used by
the following code:

old_mask = p->cpus_allowed;
set_cpus_allowed_ptr(p, new_mask);
// do_something
set_cpus_allowed_ptr(p, old_mask);

or we'd introduce another mutex to be used in both cases...  but I
think we just can get rid of most of use-cases (if not all) by
replacing them with schedule_work_on().


>
> Max
>

-- 
Best regards,
Dmitry Adamushko
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