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Path: utzoo!linus!decvax!harpo!seismo!hao!hplabs!sri-unix!Mike.Accetta@cmu-cs-ius
From: Mike.Accetta@cmu-cs-ius@sri-unix.UUCP
Newsgroups: net.unix-wizards
Subject: 4.1BSD exec() bug
Message-ID: <4190@sri-arpa.UUCP>
Date: Sat, 13-Aug-83 20:43:34 EDT
Article-I.D.: sri-arpa.4190
Posted: Sat Aug 13 20:43:34 1983
Date-Received: Mon, 15-Aug-83 01:24:58 EDT
Lines: 23

In 4.1BSD the getxfile() routine in module sys1.c contains a test against
executing a shareable text image which is open for writing.  In our version
of the system (and some others I've seen recently) the test line reads

	if (fp->f_inode == ip && (fp->f_flag&FWRITE)) {

while it should really be something like

	if (fp->f_count && fp->f_inode == ip && (fp->f_flag&FWRITE)) {

so that the file table entry is not considered when not in use.

The symptom of this bug is occasional mysterious and usually
non-repeatable "text file busy" error messages when trying to execute a
program.  These will occur whenever the system makes the check (which is
not necessarily very often given the preceding tests) and the
inode slot of the program was previously used for a file open for
writing and its corresponding entry in the file table has yet to be
reallocated.

This bug appears to have been fixed in versions of 4.1c I've seen.

			- Mike Accetta