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Re: Diff can't find its temp file - regression in trunk since 1.5.4

From: Julian Foad <julianfoad_at_btopenworld.com>
Date: Fri, 07 Nov 2008 18:06:13 +0000

On Thu, 2008-11-06 at 20:11 -0800, Greg Stein wrote:
> Gah... I've tracked this down to an APR bug.
>
> Sigh.
>
> What a freakin' bitch to find, too.
>
> Here is the basic story of what is happening:
>
> * RA needs a temp file to spool a request body, gets a temp file
> (delete on close). Call it TEMPFILE.
> * RA writes into that file, later it will be rewound, and passed to
> Neon for sending up to the server
> * The first external diff happens and the "child pool cleanup"
> executes. This closes and unlinks the file.
> * RA has no problem. It still has an open file handle.
> * The diff processing code needs a temporary file. Gets TEMPFILE since
> it is no longer present.
> * Fork off a diff process. Child cleanup code runs for the ORIGINAL
> TEMPFILE request -- closes and unlinks the file.
> * diff process no longer sees the file.
>
> The problem here is that the child unlinks the file. It should close
> it, but NOT unlink it. This is a core bug in APR.
>
> Net effect: if we have any code with APR_DELONCLOSE, *and* the file
> spans a subprocess creation, then it could invoke this bug.
>
> We can probably switch these to deleting upon pool cleanup. The only
> "real" difference is stacking up temp files for longer than before,
> but the pools should eventually go away, and the tempfiles should
> disappear.
>
> I'm going to audit all of our DELONCLOSE usage now.
>
> What a bitch...

Wow. Good detective work.

- Julian

> Cheers,
> -g
>
> On Mon, Nov 3, 2008 at 6:46 AM, Julian Foad <julianfoad_at_btopenworld.com> wrote:
> > On Mon, 2008-11-03 at 07:42 -0600, Hyrum K. Wright wrote:
> >> Julian Foad wrote:
> >> > On Mon, 2008-11-03 at 11:08 +0000, Julian Foad wrote:
> >> >> Bug: A repos-repos diff of two or more modified files fails on the
> >> >> second file with a problem accessing a local temporary file.
> >> >>
> >> >> Using trunk_at_34019 over HTTP (neon):
> >> >>
> >> >> [[[
> >> > [...]
> >> >> diff: /tmp/tempfile.5.tmp: No such file or directory
> >> >> /home/julianfoad/src/subversion-trunk/subversion/libsvn_subr/io.c:2266:
> >> >> (apr_err=200012)
> >> >> svn: '/home/julianfoad/bin/svn-external-diff' returned 2
> >> >> /home/julianfoad/src/subversion-trunk/subversion/libsvn_ra_neon/util.c:1240: (apr_err=175002)
> >> >> svn: Error reading spooled REPORT request response
> >> >> ]]]
> >> >
> >> > As you can see, I'm using an external diff. Here's a more direct way to
> >> > reproduce it, avoiding my "svn-external-diff" script:
> >> >
> >> > [[[
> >> > $ # The directory '/tmp/svn-null-config' does not exist.
> >> > $ # The external command 'diff' is GNU diff 2.8.7, found in my PATH.
> >> > $ svn --config-dir /tmp/svn-null-config diff -c34003 $SVN_REPOS
> >> > --diff-cmd=diff
> >> > Index: trunk/subversion/include/svn_auth.h
> >> > ===================================================================
> >> > --- trunk/subversion/include/svn_auth.h (revision 34002)
> >> > +++ trunk/subversion/include/svn_auth.h (revision 34003)
> >> > [...the diff of this first file is fine...]
> >> > Index: trunk/subversion/libsvn_ra_serf/serf.c
> >> > ===================================================================
> >> > diff: /tmp/tempfile.5.tmp: No such file or directory
> >> > /home/julianfoad/src/subversion-tc3/subversion/libsvn_subr/io.c:2266:
> >> > (apr_err=200012)
> >> > svn: 'diff' returned 2
> >> > /home/julianfoad/src/subversion-tc3/subversion/libsvn_ra_neon/util.c:1240: (apr_err=175002)
> >> > svn: Error reading spooled REPORT request response
> >> > ]]]
> >>
> >> If I had to guess, I'd say that it's related to r33977. All of the changes in
> >> that rev were supposed to be idempotent, but that may not be true. (Or,
> >> something was relying upon implementation-specific functionality which wasn't in
> >> the public API.)
> >
> > Testing...
> >
> > r33977 exhibits this bug.
> >
> > r33976 does not.
> >
> > Looks like you're right. Thanks.
> >
> > - Julian
> >
> >
> >
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> >
>
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Received on 2008-11-07 19:06:35 CET

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