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Subject: Re: [PATCH -v2 6/8] kexec jump: fix for lockdep
From: Huang Ying <ying.huang@intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>, Pavel Machek <pavel@ucw.cz>,
       nigel@nigel.suspend2.net, "Rafael J. Wysocki" <rjw@sisk.pl>,
       Andrew Morton <akpm@linux-foundation.org>,
       Vivek Goyal <vgoyal@redhat.com>, mingo@elte.hu,
       Linus Torvalds <torvalds@linux-foundation.org>,
       linux-kernel@vger.kernel.org,
       Kexec Mailing List <kexec@lists.infradead.org>
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Date: Mon, 11 Aug 2008 14:32:24 +0800
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On Mon, 2008-08-11 at 08:09 +0200, Peter Zijlstra wrote:
> On Mon, 2008-08-11 at 08:59 +0800, Huang Ying wrote:
> > On Fri, 2008-08-08 at 12:13 +0200, Peter Zijlstra wrote:
> > > On Fri, 2008-08-08 at 14:52 +0800, Huang Ying wrote:
> > > > Replace local_irq_disable() with raw_local_irq_disable() to prevent
> > > > lockdep complain.
> > > Uhhm, please provide more information - just using raw_* to silence
> > > lockdep is generally the wrong thing to do.
> > 
> > In traditional kexec, the new kernel will replace current one, so the
> > irq is simply disabled. But now jumping back from kexeced kernel is
> > supported, so the irq should be enabled again.
> > 
> > The code sequence of irq during kexec jump is as follow:
> > 
> > local_irq_disable(); /* in kernel_kexec() */
> > local_irq_disable(); /* in machine_kexec() */
> > local_irq_enable(); /* in kernel_kexec() */
> > 
> > The disable and enable is not match. Maybe another method is to use
> > local_irq_save(), local_irq_restore() pair in machine_kexec(), so the
> > disable and enable is matched.
> 
> And its the machine kernel's lockdep instance that goes complain?
> 
> whichever annotation gets used - and I think I can agree that raw_*
> might be approriate there, this should be accompanied with a rather
> elaborate changelog and preferably a comment in the code too. Without
> such we'll be wondering in the years to come WTH happens here.

Sorry, I find there is no complain from lockdep. Un-paired irq
disable/enable has no problem with lockdep, just increase something such
as "redundant_hardirqs_off". Please ignore this thread.

Best Regards,
Huang Ying