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

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Date:	Thu, 08 Jan 2009 01:06:02 +1030
From:	David Newall <davidn@...idnewall.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Nick Andrew <nick@...k-andrew.net>,
	Linas Vepstas <linasvepstas@...il.com>, david@...g.hm,
	Kyle Moffett <kyle@...fetthome.net>,
	Ben Goodger <goodgerster@...il.com>,
	Robert Hancock <hancockr@...w.ca>,
	linux-kernel@...r.kernel.org,
	"Jeffrey J. Kosowsky" <jeff@...owsky.org>,
	MentalMooMan <slashdot@...eshallam.info>,
	Travis Crump <pretzalz@...hhouse.org>, burdell@...ntheinter.net
Subject: Re: Bug: Status/Summary of slashdot leap-second crash on new years
 2008-2009

Alan Cox wrote:
>>> The RTC stores the CMOS time in MM DD YY HH:MM:SS format.
>>>       
>> Yes, which is perfect for mktime(), which knows about leap seconds and
>> so produces the correct time_t.
>>     
>
> mktime in the kernel has no knowledge of leap seconds whatsoever. Go read
> kernel/time.c
>   
Is there a mktime() in the kernel?  Isn't it pure user-space?  Mktime
does appear to know all about leap seconds (assuming they're in zoneinfo.)


>> different understanding.  I thought it was said that there's kernel
>> support to handle the leap second flag in NTP's broadcasts, and that
>> that was where the bug was.
>>     
>
> All the kernel knows how to do is to slew time (in general) and to repeat
> or remove one second. It has no knowledge of leap seconds and it doesn't
> know how to convert between UTC/TAI/Unix Epoch etc.

I went back to the start of the thread.  Chris posted a stack trace
showing "#15 0xffffffff8104ec16 in ntp_leap_second (timer=<value
optimized out>) at kernel/time/ntp.c:143".  That would be kernel code to
process leap seconds from NTP broadcasts, I think.  That code needs to
be removed.
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