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

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Date:	Wed, 24 Jan 2007 08:30:47 -0800
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Pavel Machek <pavel@....cz>
Cc:	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 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
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