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Subject: Re: [patch] fix emergency reboot: call reboot notifier list if possible
Date: Wed, 24 Jan 2007 12:49:32 -0500
Message-ID: <Pine.LNX.4.61.0701241247290.4476@chaos.analogic.com>
In-Reply-To: <20070124083047.37b09f2c.randy.dunlap@oracle.com>
Thread-Topic: [patch] fix emergency reboot: call reboot notifier list if possible
Thread-Index: Acc/4AKTuNb6KR5RSBqOwJwL/2fEWw==
References: <20070117091319.GA30036@elte.hu><20070117092233.GA30197@flint.arm.linux.org.uk><20070117093917.GA7538@elte.hu><20070117020343.8622e44d.akpm@osdl.org><20070123195712.GB6596@ucw.cz> <20070124083047.37b09f2c.randy.dunlap@oracle.com>
From: "linux-os \(Dick Johnson\)" <linux-os@analogic.com>
To: "Randy Dunlap" <randy.dunlap@oracle.com>
Cc: "Pavel Machek" <pavel@ucw.cz>, "Andrew Morton" <akpm@osdl.org>,
       "Ingo Molnar" <mingo@elte.hu>, <rmk+lkml@arm.linux.org.uk>,
       <linux-kernel@vger.kernel.org>
Reply-To: "linux-os \(Dick Johnson\)" <linux-os@analogic.com>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2970
Lines: 66


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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