User app corrupting buffer cache.

Mark Salter (
Fri, 27 Jun 1997 15:05:45 -0500

I am running into a strange problem where a user-level program
is causing the buffer cache to be corrupted. I have verified this
corruption on a several 2.0 kernels including 2.0.30, and on
2.1.40. The binary that I am running is a postscript interpreter
which sends a rendered bitmap to stdout. I am sure that the
application binary has bugs :-) but am concerned that it corrupts
the buffer cache.

I am running into this problem on a PPro with 64MB of RAM. I
have turned off swapping and am running from the login console
with no X windows or networking running.

Here is a typical failure:

> ps_app -obitmap -z >/dev/null
Segmentation fault

This looks straightforward enough. Just an application bug, you
say. Well, the problem is that the buffer cache is now corrupted.
If I "cksum ps_app", I'll get a different result than when I
cksum it before running. Same goes for If I then:

> cp

and reboot, and differ. has only
printable ascii characters in it, but will have
some number (usually less than 100) of non-ascii bytes scattered
throughout it.

Other parts of the buffer cache will be corrupted also. If I am
running emacs and then run ps_app, emacs will often times crash
or give various error messages. Trying to start any other apps
after running ps_app will usually fail.

I am certain (almost) that the problem is not hardware. This
PC running 2.0.30 kernel will run flawlessly under varying
and often heavy loads as long as I don't run this particular

Any comments or suggestions on how to track down this problem?

Mark Salter
Member of Technical Staff
QMS, Inc.
Mobile, AL 36618