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

From
SZEDER Gábor <szeder.dev@gmail.com>
Date
Sep 27, 2019, 02:17 UTC
Message-ID
<20190927021746.GL2637@szeder.dev>
In-Reply-To
<20190927010930.GK2637@szeder.dev>
On Fri, Sep 27, 2019 at 03:09:30AM +0200, SZEDER Gábor wrote:
Show 42 quoted lines
> 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.

Indeed, with 404ebceda0 the test below segfaults on case insensitive fs, but not on a case sensitive one.

diff --git a/t/t0050-filesystem.sh b/t/t0050-filesystem.sh
index 192c94eccd..5b405c97d7 100755
--- a/t/t0050-filesystem.sh
+++ b/t/t0050-filesystem.sh
@@ -131,4 +131,27 @@ $test_unicode 'merge (silent unicode normalization)' '
 	git merge topic
 '
 
+test_expect_success CASE_INSENSITIVE_FS "Denton's segfault" '
+	git init repo &&
+	(
+		cd repo &&
+
+		echo foo >Gitweb &&
+		git add Gitweb &&
+		git commit -m "add Gitweb" &&
+
+		git checkout --orphan todo &&
+		git reset --hard &&
+		# the subdir is crucial, without it there is no segfault
+		mkdir -p gitweb/subdir &&
+		echo bar >gitweb/subdir/file &&
+		# it is not strictly necessary to add and commit the
+		# gitweb directory, its presence is sufficient
+		git add gitweb &&
+		git commit -m "add gitweb/subdir/file" &&
+
+		git checkout master
+	)
+'
+
 test_done



The end of its trace:

++git checkout master
./test-lib.sh: line 910: 11220 Segmentation fault: 11  git checkout master
error: last command exited with $?=139

Case insensitivity is important because check_ok_to_remove() is
invoked from verify_absent_1(), which looks like this:

  if (...)
     ....
  else if (...)
     ....
  else if (lstat(ce->name, &st))
      // That lstat() checked whether 'Gitweb' is absent.  On a case
      // sensitive fs it's absent, so it returns.  On a case
      // insensitive fs it finds 'master's 'gitweb' directory, so it
      // goes on to the else below, and eventually segfaults.
      return;
  else
      check_ok_to_remove()


Good night :)
Previous: SZEDER GáborNext: Denton Liu
Message 53 of 73 in “t7300-clean: demonstrate deleting nested repo with an ignored file breakage”
  1. t7300-clean: demonstrate deleting nested repo with an ignored file breakageSZEDER Gábor, Aug 25, 2019
  2. SZEDER GáborAug 25, 2019
  3. Philip OakleyAug 25, 2019
  4. SZEDER GáborAug 26, 2019
  5. 00/12 Fix some git clean issuesElijah Newren, Sep 5, 2019
  6. 01/12 t7300: Add some testcases showing failure to clean specified pathspecsElijah Newren, Sep 5, 2019
  7. 02/12 dir: fix typo in commentElijah Newren, Sep 5, 2019
  8. 04/12 dir: Directories should be checked for matching pathspecs tooElijah Newren, Sep 5, 2019
  9. 03/12 dir: fix off-by-one error in match_pathspec_itemElijah Newren, Sep 5, 2019
  10. 05/12 dir: Make the DO_MATCH_SUBMODULE code reusable for a non-submodule caseElijah Newren, Sep 5, 2019
  11. 07/12 dir: add commentary explaining match_pathspec_item's return valueElijah Newren, Sep 5, 2019
  12. 06/12 dir: If our pathspec might match files under a dir, recurse into itElijah Newren, Sep 5, 2019
  13. 10/12 clean: avoid removing untracked files in a nested git repositoryElijah Newren, Sep 5, 2019
  14. SZEDER GáborSep 5, 2019
  15. 09/12 clean: disambiguate the definition of -dElijah Newren, Sep 5, 2019
  16. 11/12 clean: rewrap overly long lineElijah Newren, Sep 5, 2019
  17. 12/12 clean: fix theoretical path corruptionElijah Newren, Sep 5, 2019
  18. SZEDER GáborSep 5, 2019
  19. Elijah NewrenSep 7, 2019
  20. 08/12 git-clean.txt: do not claim we will delete files with -n/--dry-runElijah Newren, Sep 5, 2019
  21. SZEDER GáborSep 5, 2019
  22. Elijah NewrenSep 7, 2019
  23. 00/12 Fix some git clean issuesElijah Newren, Sep 12, 2019
  24. 01/12 t7300: add testcases showing failure to clean specified pathspecsElijah Newren, Sep 12, 2019
  25. Junio C HamanoSep 13, 2019
  26. Elijah NewrenSep 13, 2019
  27. Junio C HamanoSep 13, 2019
  28. 03/12 dir: fix off-by-one error in match_pathspec_itemElijah Newren, Sep 12, 2019
  29. Junio C HamanoSep 13, 2019
  30. 02/12 dir: fix typo in commentElijah Newren, Sep 12, 2019
  31. 05/12 dir: make the DO_MATCH_SUBMODULE code reusable for a non-submodule caseElijah Newren, Sep 12, 2019
  32. 04/12 dir: also check directories for matching pathspecsElijah Newren, Sep 12, 2019
  33. 06/12 dir: if our pathspec might match files under a dir, recurse into itElijah Newren, Sep 12, 2019
  34. Junio C HamanoSep 13, 2019
  35. 07/12 dir: add commentary explaining match_pathspec_item's return valueElijah Newren, Sep 12, 2019
  36. Junio C HamanoSep 13, 2019
  37. 09/12 clean: disambiguate the definition of -dElijah Newren, Sep 12, 2019
  38. 10/12 clean: avoid removing untracked files in a nested git repositoryElijah Newren, Sep 12, 2019
  39. 11/12 clean: rewrap overly long lineElijah Newren, Sep 12, 2019
  40. 08/12 git-clean.txt: do not claim we will delete files with -n/--dry-runElijah Newren, Sep 12, 2019
  41. 12/12 clean: fix theoretical path corruptionElijah Newren, Sep 12, 2019
  42. 00/12 Fix some git clean issuesElijah Newren, Sep 17, 2019
  43. 02/12 dir: fix typo in commentElijah Newren, Sep 17, 2019
  44. 01/12 t7300: add testcases showing failure to clean specified pathspecsElijah Newren, Sep 17, 2019
  45. 03/12 dir: fix off-by-one error in match_pathspec_itemElijah Newren, Sep 17, 2019
  46. 04/12 dir: also check directories for matching pathspecsElijah Newren, Sep 17, 2019
  47. [BUG] git is segfaulting, was [PATCH v4 04/12] dir: also check directories for matching pathspecsDenton Liu, Sep 25, 2019
  48. Elijah NewrenSep 25, 2019
  49. Denton LiuSep 25, 2019
  50. Denton LiuSep 26, 2019
  51. Elijah NewrenSep 27, 2019
  52. SZEDER GáborSep 27, 2019
  53. SZEDER GáborSep 27, 2019
  54. Denton LiuSep 27, 2019
  55. dir: special case check for the possibility that pathspec is NULLElijah Newren, Sep 30, 2019
  56. Denton LiuSep 30, 2019
  57. Elijah NewrenOct 1, 2019
  58. dir: special case check for the possibility that pathspec is NULLElijah Newren, Oct 1, 2019
  59. Denton LiuOct 1, 2019
  60. Elijah NewrenOct 1, 2019
  61. dir: special case check for the possibility that pathspec is NULLElijah Newren, Oct 1, 2019
  62. Denton LiuOct 1, 2019
  63. Elijah NewrenOct 1, 2019
  64. Elijah NewrenOct 2, 2019
  65. SZEDER GáborOct 7, 2019
  66. 08/12 git-clean.txt: do not claim we will delete files with -n/--dry-runElijah Newren, Sep 17, 2019
  67. 11/12 clean: rewrap overly long lineElijah Newren, Sep 17, 2019
  68. 12/12 clean: fix theoretical path corruptionElijah Newren, Sep 17, 2019
  69. 09/12 clean: disambiguate the definition of -dElijah Newren, Sep 17, 2019
  70. 10/12 clean: avoid removing untracked files in a nested git repositoryElijah Newren, Sep 17, 2019
  71. 07/12 dir: add commentary explaining match_pathspec_item's return valueElijah Newren, Sep 17, 2019
  72. 06/12 dir: if our pathspec might match files under a dir, recurse into itElijah Newren, Sep 17, 2019
  73. 05/12 dir: make the DO_MATCH_SUBMODULE code reusable for a non-submodule caseElijah Newren, Sep 17, 2019

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