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Date: Wed, 25 Apr 2001 18:10:16 -0700
From: Andrew Morton <andrewm@uow.edu.au>
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To: Tobias Ringstrom <tori@tellus.mine.nu>
CC: Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Weird problem with 2.4.4-pre6
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Tobias Ringstrom wrote:
> 
> Yesterday, I was running tcpdump, paging the output with less.  All of a
> sudden, less started to dump core (SIGSEGV).  I could not even start less
> by itself:
> 
>     > less
> 
> without it getting a SIGSEGV, and in fact no user could run less without
> getting a SIGSEGV, but it did work perfectly a few minutes earlier.  This
> morning, I tried to run less again, and now it was working!  No core
> dumps!
> 
> How can this happen?  Something overwriting the page/buffer cache?

Yes.  Something scribbled on the pagecache, most likely.

If this happens, take a copy of the offending binary and all its shared
libraries - simply copy them into a temp directory.  The corrupted version
will be written to disk, from the pagecache.  Make sure you keep
a copy of the offending vmlinux as well for looking things up in.

Then reboot and start diffing things; the differences can provide
clues.  If the diffs show single-bit errors then it's a RAM
problem.  If the diffs look like pointers into kernel space
then look 'em up in vmlinux and shout loudly.  etc.

-
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