linux-kernel - Re: Bug: Status/Summary of slashdot leap-second crash on new years 2008-2009

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Message-ID: <3ae3aa420901021945w3d8f8065p2cd3e4f649849a2e@mail.gmail.com>
Date:	Fri, 2 Jan 2009 21:45:16 -0600
From:	"Linas Vepstas" <linasvepstas@...il.com>
To:	"Duane Griffin" <duaneg@...da.com>
Cc:	"Chris Adams" <cmadams@...aay.net>, linux-kernel@...r.kernel.org
Subject: Re: Bug: Status/Summary of slashdot leap-second crash on new years 2008-2009

2009/1/2 Duane Griffin <duaneg@...da.com>:
> On Fri, Jan 02, 2009 at 06:21:14PM -0600, Chris Adams wrote:
>> Once upon a time, Linas Vepstas <linasvepstas@...il.com> said:
>> > Below follows a summary of the reported crashes. I'm ignoring the
>> > zillions of "mine didn't crash" reports, or the "you're a paranoid
>> > conspiracy theorist, its random chance" reports.
>>
>> I have reproduced this and got a stack trace (this is with Fedora 8 and
>> kernel kernel-2.6.26.6-49.fc8.x86_64):
>>
>> Basically (to my untrained eye), the leap second code is called from the
>> timer interrupt handler, which holds xtime_lock.  The leap second code
>> does a printk to notify about the leap second.  The printk code tries to
>> wake up klogd (I assume to prioritize kernel messages), and (under some
>> conditions), the scheduler attempts to get the current time, which tries
>> to get xtime_lock => deadlock.
>
> How about just moving the printk out of the lock? I.e. something like
> this:

[...]

Sure looks like the right fix to me.  (Although there's more than
one printk under that lock).  Who's going to write the formal patch?

--linas
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