linux-kernel - Re: [patch] fix emergency reboot: call reboot notifier list if possible

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Message-ID: <Pine.LNX.4.61.0701241247290.4476@chaos.analogic.com>
Date:	Wed, 24 Jan 2007 12:49:32 -0500
From:	"linux-os \(Dick Johnson\)" <linux-os@...logic.com>
To:	"Randy Dunlap" <randy.dunlap@...cle.com>
Cc:	"Pavel Machek" <pavel@....cz>, "Andrew Morton" <akpm@...l.org>,
	"Ingo Molnar" <mingo@...e.hu>, <rmk+lkml@....linux.org.uk>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [patch] fix emergency reboot: call reboot notifier list if possible

On Wed, 24 Jan 2007, Randy Dunlap wrote:

> On Tue, 23 Jan 2007 19:57:12 +0000 Pavel Machek wrote:
>
>> Hi!
>>
>>>>> On Wed, Jan 17, 2007 at 10:13:19AM +0100, Ingo Molnar wrote:
>>>>>> we dont call the reboot notifiers during emergency reboot mainly because
>>>>>> it could be called from atomic context and reboot notifiers are a
>>>>>> blocking notifier list. But actually the kernel is often perfectly
>>>>>> reschedulable in this stage, so we could as well process the
>>>>>> reboot_notifier_list.
>>>>>
>>>>> My experience has been that when there has been the need to use this
>>>>> facility, the kernel hasn't been reschedulable. [...]
>>>>
>>>> this decision is totally automatic - so if your situation happens and
>>>> the kernel isnt reschedulable, then the notifier chain wont be called
>>>> and nothing changes from your perspective. Hm, perhaps this should be
>>>> dependent on CONFIG_PREEMPT, to make sure preempt_count() is reliable?
>>>>
>>>> but from my perspective this patch fixes a real regression.
>>>>
>>>> updated patch attached below.
>>>>
>>>
>>> Making it dependent upon CONFIG_PREEMPT seems a bit sucky.  Perhaps pass in
>>> some "you were called from /proc/sysrq-trigger" notification?
>>
>> What about adding 'B' with 'reboot with notifications' meaning?
>
> if I am reading 'B' vs. 'b' correctly:
>
> sysrq key codes are currently all lower case only.
> Of course, that could be changed to support upper case.
> That would require sysrq help messages in a different format
> (currently the keycode for the action is Capitalized, e.g.,
> b => reBoot).  And I suspect that it would allow some users to
> enter b vs. B or B vs. b etc. unintentionally.
> In any case, the sysrq_key_table could easily fill up soon,
> so we may be force to support UpperCase codes.
>
> ---
> ~Randy

The you can take the lower scan-code and AND it with 95 (decimal)
before the test. That will allow all A-z codes to work (not numbers,
though). They get compared with the upper-case.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.16.24 on an i686 machine (5592.59 BogoMips).
New book: http://www.AbominableFirebug.com/
_
..

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