Subject: Re: [BUG] git is segfaulting, was [PATCH v4 04/12] dir: also check directories for matching pathspecs

From: SZEDER Gábor <[email-masked]>
Date: Fri, 27 Sep 2019 03:09:30 +0200

On Wed, Sep 25, 2019 at 01:39:19PM -0700, Denton Liu wrote:
> Hi Elijah,
> 
> I ran into a segfault on MacOS. I managed to bisect it down to
> 404ebceda0 (dir: also check directories for matching pathspecs,
> 2019-09-17), which should be the patch in the parent thread. The test
> case below works fine without this patch applied but segfaults once it
> is applied.
> 
> 	#!/bin/sh
> 
> 	git worktree add testdir
> 	git -C testdir checkout master
> 	git -C testdir fetch https://github.com/git/git.git todo
> 	bin-wrappers/git -C testdir checkout FETCH_HEAD # segfault here
> 
> Note that the worktree part isn't necessary to reproduce the problem but
> I didn't want my files to be constantly refreshed, triggering a rebuild
> each time.
> 
> I also managed to get this backtrace from running lldb at the segfault
> but it is based on the latest "jch" commit, 1cc52d20df (Merge branch
> 'jt/merge-recursive-symlink-is-not-a-dir-in-way' into jch, 2019-09-20).
> 
> 	* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x8)
> 	  * frame #0: 0x00000001000f63a0 git`do_match_pathspec(istate=0x0000000100299940, ps=0x000000010200aa80, name="Gitweb/static/js/lib/", namelen=21, prefix=0, seen=0x0000000000000000, flags=0) at dir.c:420:2 [opt]
> 		frame #1: 0x00000001000f632c git`match_pathspec(istate=0x0000000100299940, ps=0x0000000000000000, name="Gitweb/static/js/lib/", namelen=21, prefix=0, seen=0x0000000000000000, is_dir=0) at dir.c:490:13 [opt]
> 		frame #2: 0x00000001000f8315 git`read_directory_recursive(dir=0x00007ffeefbfe278, istate=0x0000000100299940, base=<unavailable>, baselen=17, untracked=<unavailable>, check_only=0, stop_at_first_file=0, pathspec=0x0000000000000000) at dir.c:1990:9 [opt]
> 		frame #3: 0x00000001000f82e9 git`read_directory_recursive(dir=0x00007ffeefbfe278, istate=0x0000000100299940, base=<unavailable>, baselen=14, untracked=<unavailable>, check_only=0, stop_at_first_file=0, pathspec=0x0000000000000000) at dir.c:1984:5 [opt]
> 		frame #4: 0x00000001000f82e9 git`read_directory_recursive(dir=0x00007ffeefbfe278, istate=0x0000000100299940, base=<unavailable>, baselen=7, untracked=<unavailable>, check_only=0, stop_at_first_file=0, pathspec=0x0000000000000000) at dir.c:1984:5 [opt]
> 		frame #5: 0x00000001000f60d1 git`read_directory(dir=0x00007ffeefbfe278, istate=0x0000000100299940, path="Gitweb/", len=7, pathspec=0x0000000000000000) at dir.c:2298:3 [opt]
> 		frame #6: 0x00000001001bded1 git`verify_clean_subdirectory(ce=<unavailable>, o=0x00007ffeefbfe8c0) at unpack-trees.c:1846:6 [opt]
> 		frame #7: 0x00000001001bdc1d git`check_ok_to_remove(name="Gitweb", len=6, dtype=4, ce=0x0000000103e70de0, st=0x00007ffeefbfe438, error_type=ERROR_WOULD_LOSE_UNTRACKED_OVERWRITTEN, o=0x00007ffeefbfe8c0) at unpack-trees.c:1901:7 [opt]

That 'name="Gitweb" parameter caught my eye.  origin/todo contains a
'Gitweb' file, with upper case 'G', while master contains a 'gitweb'
directory, with lower case 'g'.  

Could it be that case (in)sensitivity plays a crucial rule in
triggering the segfault?  FWIW I could reproduce it following Denton's
description on Travis CI's macOS VM with the debug shell access, and
it uses case insensitive file system.