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Re: segfault when merging

From: Paul Burba <ptburba_at_gmail.com>
Date: Wed, 24 Oct 2012 20:58:35 -0400

On Wed, Oct 24, 2012 at 7:16 PM, Paul Burba <ptburba_at_gmail.com> wrote:
> On Wed, Oct 24, 2012 at 2:14 PM, Stefan K√ľng <tortoisesvn_at_gmail.com> wrote:
>> Hi,
>>
>> There were quite a few crash reports sent for TSVN which indicate a problem
>> when merging.
>>
>> Until now I never really had a good crash dump and also no
>> user to contact.
>>
>> But now that's changed:
>> User report is here:
>> http://tortoisesvn.tigris.org/ds/viewMessage.do?dsForumId=4061&dsMessageId=3023140
>>
>> Crash dump available here:
>> https://www.crash-server.com/Problem.aspx?ClientID=tsvn&Login=Guest&ProblemID=6224
>> (you should know the login data already, if not please contact my
>> privately).
>>
>> Here's what I found so far:
>> libsvn_client\merge.c, calculate_left_hand_side()
>>
>> /* Convert the absolute path with mergeinfo on it to a path relative
>> to the session root. */
>> SVN_ERR(svn_client__path_relative_to_root(&path_rel_to_root,
>> ctx->wc_ctx, absolute_path,
>> target_repos_root, FALSE,
>> NULL, scratch_pool,
>> iterpool));
>> path_rel_to_session = svn_relpath_skip_ancestor(target_repos_rel_path,
>> path_rel_to_root);
>> SVN_ERR(svn_client__repos_location_segments(&segments,
>> target_ra_session,
>> path_rel_to_session,
>> target_rev, target_rev,
>> SVN_INVALID_REVNUM,
>> ctx, scratch_pool));
>>
>> here, the 'path_rel_to_session' is set to NULL by the
>> svn_relpath_skip_ancestor() call, which then leads to a NULL-pointer access
>> later on in svn_client__repos_location_segments and further down in
>> svn_ra_get_location_segments():
>> SVN_ERR_ASSERT(*path != '/');
>>
>> where 'path' is the NULL pointer of path_rel_to_session.
>>
>> svn_relpath_skip_ancestor() returns NULL if the paths are not related or if
>> the second argument string does not end with a '/'.
>
> FWIW the second arg does not need to end with a '/' for a non-NULL return value.
>
>> Gathering from the crash dump I can see that the second argument points to a
>> file so it does not end with a '/' char.
>>
>> The two strings passed to svn_relpath_skip_ancestor() are according to the
>> crash dump:
>> somename/branches/dev62
>> and
>> shared/trunk/somefile.bas
>>
>> (somename and somefile used to protect the innocent).
>>
>> I hope this helps to figure out why the crash happens - I'm not familiar
>> with the merge code so someone else needs to look at this.
>
> I think I found the problem. The user mentioned he has "several
> Externals as files, no folders, which may be worth mentioning as a
> potential source of problem." I can produce a segfault during a merge
> if the file externals in the reintegrate target have svn:mergeinfo set
> on them. We should ignore these file externals as far as merge
> tracking is concerned, but we aren't. Fixed on trunk in r1401915.

I also nominated r1401915 for backport to 1.7.x.

-- 
Paul T. Burba
CollabNet, Inc. -- www.collab.net -- Enterprise Cloud Development
Skype: ptburba
Received on 2012-10-25 02:59:07 CEST

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