linux-kernel - Re: `make dep' with clock skew detected loops forever

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Message-ID: <20120305153309.GA31864@linux.vnet.ibm.com>
Date:	Mon, 5 Mar 2012 07:33:09 -0800
From:	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>
To:	Michal Marek <mmarek@...e.cz>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-kbuild@...r.kernel.org
Subject: Re: `make dep' with clock skew detected loops forever

On 05.03.2012 [15:40:56 +0100], Michal Marek wrote:
> On 29.2.2012 20:01, Nishanth Aravamudan wrote:
> > Noticed something on a fresh FC16 based install on a test server in our
> > lab.  Autotest by default runs `make dep` and it seems the clock is
> > pretty badly skewed on this server, resulting in an infinite loop of:
> > 
> > 01:09:37 DEBUG| Running 'make dep'
> > 01:09:38 DEBUG| [stderr] make: Warning: File `/usr/local/autotest/tmp/build/linux/arch/powerpc/Makefile' has modification time 112143 s in the future
> > 01:09:38 DEBUG| [stderr] make[1]: Warning: File `/usr/local/autotest/tmp/build/linux/arch/powerpc/Makefile' has modification time 112143 s in the future
> > 01:09:38 DEBUG| [stderr] make[2]: Warning: File `scripts/Makefile.host' has modification time 112143 s in the future
> > 01:09:38 DEBUG| [stdout]   HOSTCC  scripts/basic/fixdep
> > 01:09:38 DEBUG| [stderr] make[2]: warning:  Clock skew detected.  Your build may be incomplete.
> > 01:09:38 DEBUG| [stderr] make[2]: Warning: File `scripts/Makefile.host' has modification time 112143 s in the future
> [...]
> 
> > Anyone know why that happens?
> 
> Because the system time time is several hours, if not days, behind, so
> generated files are older than source files and thus dependencies cannot
> work. You need to fix the system time to be at least ahead of the mtime
> of the sources.

That makes sense.

> > Obvious fixes are to either not run `make dep`
> 
> I don't think this is limited to make dep.

Well, killing `make dep`, which was just looping, and executing `make
-j16 vmlinux` did seem to complete. But it was a while ago and maybe I'm
mis-remembering.

Ah well, I've fixed up my testing scripts to ensure an ntp run is
performed before trying to build.

Thanks,
Nish

-- 
Nishanth Aravamudan <nacc@...ibm.com>
IBM Linux Technology Center

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