Issue #16814 has been updated by mame (Yusuke Endoh).


> disappeared on April 15.

You may know, but the test has been skipped on s390x since 9948addda67f4b7a6e3575f1eba9025f998811d2.

----------------------------------------
Bug #16814: Segmentation fault in GC while running test/ruby/test_fiber.rb on s390x
https://bugs.ruby-lang.org/issues/16814#change-85275

* Author: ReiOdaira (Rei Odaira)
* Status: Open
* Priority: Normal
* ruby -v: ruby 2.8.0dev (2020-04-12T03:45:22Z master 5c27681813) [s390x-linux]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
A segmentation fault almost always happens in test/ruby/test_fiber.rb with certain commits of latest Ruby on s390x.

```
$ make test-all TESTS=test/ruby/test_fiber.rb
Run options:
  --seed=90044
  "--ruby=./miniruby -I./lib -I. -I.ext/common  ./tool/runruby.rb --extout=.ext  -- --disable-gems"
  --excludes-dir=./test/excludes
  --name=!/memory_leak/

# Running tests:

[24/29] TestFiber#test_stack_size = 0.89 s
  1) Failure:
TestFiber#test_stack_size [/home/chkbuild/my-tmp/build/20200412T043305Z/ruby/test/ruby/test_fiber.rb:356]:
pid 5713 killed by SIGABRT (signal 6) (core dumped)
| -e:1:in `print': stack level too deep (SystemStackError)
|       from -e:1:in `rec'
|       from -e:1:in `block (3 levels) in rec'
|       from -e:1:in `times'
|       from -e:1:in `block (2 levels) in rec'
|       from -e:1:in `times'
|       from -e:1:in `block in rec'
|       from -e:1:in `times'
|       from -e:1:in `rec'
|        ... 172 levels...
|       from -e:1:in `block in rec'
| -e: [BUG] Segmentation fault at 0x0000000000000000
| ruby 2.8.0dev (2020-04-12T03:45:22Z master 5c27681813) [s390x-linux]
|
| -- Control frame information -----------------------------------------------
| c:0001 p:0000 s:0003 E:001e20 (none) [FINISH]
|
|
| -- Other runtime information -----------------------------------------------
|
| * Loaded script: -e
|
| * Loaded features:
|
|     0 enumerator.so
|     1 thread.rb
|     2 rational.so
|     3 complex.so
|     4 ruby2_keywords.rb
|     5 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/.ext/s390x-linux/enc/encdb.so
|     6 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/.ext/s390x-linux/enc/trans/transdb.so
|     7 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/rbconfig.rb
|     8 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/rubygems/compatibility.rb
|     9 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/rubygems/defaults.rb
|    10 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/rubygems/deprecate.rb
|    11 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/rubygems/errors.rb
|    12 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/rubygems/version.rb
|    13 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/rubygems/requirement.rb
|    14 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/rubygems/platform.rb
|    15 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/rubygems/basic_specification.rb
|    16 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/rubygems/stub_specification.rb
|    17 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/rubygems/util.rb
|    18 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/rubygems/text.rb
|    19 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/rubygems/user_interaction.rb
|    20 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/rubygems/specification_policy.rb
|    21 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/rubygems/util/list.rb
|    22 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/rubygems/specification.rb
|    23 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/rubygems/exceptions.rb
|    24 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/rubygems/bundler_version_finder.rb
|    25 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/rubygems/dependency.rb
|    26 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/rubygems/core_ext/kernel_gem.rb
|    27 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/.ext/s390x-linux/monitor.so
|    28 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/.ext/common/monitor.rb
|    29 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/rubygems/core_ext/kernel_require.rb
|    30 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/rubygems/core_ext/kernel_warn.rb
|    31 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/rubygems.rb
|    32 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/did_you_mean/version.rb
|    33 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/did_you_mean/core_ext/name_error.rb
|    34 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/did_you_mean/levenshtein.rb
|    35 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/did_you_mean/jaro_winkler.rb
|    36 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/did_you_mean/spell_checker.rb
|    37 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/did_you_mean/spell_checkers/name_error_checkers/class_name_checker.rb
|    38 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/did_you_mean/spell_checkers/name_error_checkers/variable_name_checker.rb
|    39 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/did_you_mean/spell_checkers/name_error_checkers.rb
|    40 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/did_you_mean/spell_checkers/method_name_checker.rb
|    41 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/did_you_mean/spell_checkers/key_error_checker.rb
|    42 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/did_you_mean/spell_checkers/null_checker.rb
|    43 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/did_you_mean/formatters/plain_formatter.rb
|    44 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/did_you_mean/tree_spell_checker.rb
|    45 /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/lib/did_you_mean.rb
|
| * Process memory map:
|
| 2aa15380000-2aa15772000 r-xp 00000000 5e:01 1198050                      /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/ruby
| 2aa15772000-2aa15777000 r--p 003f1000 5e:01 1198050                      /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/ruby
| 2aa15777000-2aa15779000 rw-p 003f6000 5e:01 1198050                      /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/ruby
| 2aa15779000-2aa15787000 rw-p 00000000 00:00 0
| 2aa29766000-2aa29ab0000 rw-p 00000000 00:00 0                            [heap]
| 3ffaa180000-3ffaa182000 r-xp 00000000 5e:01 1197862                      /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/.ext/s390x-linux/monitor.so
| 3ffaa182000-3ffaa183000 r--p 00001000 5e:01 1197862                      /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/.ext/s390x-linux/monitor.so
| 3ffaa183000-3ffaa184000 rw-p 00002000 5e:01 1197862                      /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/.ext/s390x-linux/monitor.so
| 3ffaa200000-3ffaa202000 r-xp 00000000 5e:01 1198135                      /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/.ext/s390x-linux/enc/trans/transdb.so
| 3ffaa202000-3ffaa203000 ---p 00002000 5e:01 1198135                      /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/.ext/s390x-linux/enc/trans/transdb.so
| 3ffaa203000-3ffaa204000 r--p 00002000 5e:01 1198135                      /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/.ext/s390x-linux/enc/trans/transdb.so
| 3ffaa204000-3ffaa205000 rw-p 00003000 5e:01 1198135                      /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/.ext/s390x-linux/enc/trans/transdb.so
| 3ffaab76000-3ffacc80000 rw-p 00000000 00:00 0
| 3ffacc80000-3ffacc82000 r-xp 00000000 5e:01 133388                       /usr/lib64/libfreebl3.so
| 3ffacc82000-3ffacc83000 r--p 00001000 5e:01 133388                       /usr/lib64/libfreebl3.so
| 3ffacc83000-3ffacc84000 rw-p 00002000 5e:01 133388                       /usr/lib64/libfreebl3.so
| 3ffacd00000-3ffaceaf000 r-xp 00000000 5e:01 134626                       /usr/lib64/libc-2.17.so
| 3ffaceaf000-3ffaceb3000 r--p 001ae000 5e:01 134626                       /usr/lib64/libc-2.17.so
| 3ffaceb3000-3ffaceb5000 rw-p 001b2000 5e:01 134626                       /usr/lib64/libc-2.17.so
| 3ffaceb5000-3ffaceb9000 rw-p 00000000 00:00 0
| 3ffacf00000-3ffacfa8000 r-xp 00000000 5e:01 135803                       /usr/lib64/libm-2.17.so
| 3ffacfa8000-3ffacfa9000 r--p 000a7000 5e:01 135803                       /usr/lib64/libm-2.17.so
| 3ffacfa9000-3ffacfaa000 rw-p 000a8000 5e:01 135803                       /usr/lib64/libm-2.17.so
| 3ffad000000-3ffad00d000 r-xp 00000000 5e:01 135760                       /usr/lib64/libcrypt-2.17.so
| 3ffad00d000-3ffad00e000 r--p 0000c000 5e:01 135760                       /usr/lib64/libcrypt-2.17.so
| 3ffad00e000-3ffad00f000 rw-p 0000d000 5e:01 135760                       /usr/lib64/libcrypt-2.17.so
| 3ffad00f000-3ffad03d000 rw-p 00000000 00:00 0
| 3ffad080000-3ffad083000 r-xp 00000000 5e:01 135797                       /usr/lib64/libdl-2.17.so
| 3ffad083000-3ffad084000 r--p 00002000 5e:01 135797                       /usr/lib64/libdl-2.17.so
| 3ffad084000-3ffad085000 rw-p 00003000 5e:01 135797                       /usr/lib64/libdl-2.17.so
| 3ffad100000-3ffad187000 r-xp 00000000 5e:01 136942                       /usr/lib64/libgmp.so.10.2.0
| 3ffad187000-3ffad189000 r--p 00086000 5e:01 136942                       /usr/lib64/libgmp.so.10.2.0
| 3ffad189000-3ffad18a000 rw-p 00088000 5e:01 136942                       /usr/lib64/libgmp.so.10.2.0
| 3ffad200000-3ffad208000 r-xp 00000000 5e:01 136149                       /usr/lib64/librt-2.17.so
| 3ffad208000-3ffad209000 r--p 00007000 5e:01 136149                       /usr/lib64/librt-2.17.so
| 3ffad209000-3ffad20a000 rw-p 00008000 5e:01 136149                       /usr/lib64/librt-2.17.so
| 3ffad280000-3ffad298000 r-xp 00000000 5e:01 135793                       /usr/lib64/libpthread-2.17.so
| 3ffad298000-3ffad299000 r--p 00017000 5e:01 135793                       /usr/lib64/libpthread-2.17.so
| 3ffad299000-3ffad29a000 rw-p 00018000 5e:01 135793                       /usr/lib64/libpthread-2.17.so
| 3ffad29a000-3ffad29e000 rw-p 00000000 00:00 0
| 3ffad300000-3ffad317000 r-xp 00000000 5e:01 136264                       /usr/lib64/libz.so.1.2.7
| 3ffad317000-3ffad318000 r--p 00016000 5e:01 136264                       /usr/lib64/libz.so.1.2.7
| 3ffad318000-3ffad319000 rw-p 00017000 5e:01 136264                       /usr/lib64/libz.so.1.2.7
| 3ffad380000-3ffad382000 r-xp 00000000 5e:01 1198055                      /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/.ext/s390x-linux/enc/encdb.so
| 3ffad382000-3ffad383000 r--p 00001000 5e:01 1198055                      /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/.ext/s390x-linux/enc/encdb.so
| 3ffad383000-3ffad384000 rw-p 00002000 5e:01 1198055                      /home/chkbuild/my-tmp/build/20200412T043305Z/ruby/.ext/s390x-linux/enc/encdb.so
| 3ffad39f000-3ffad400000 rw-p 00000000 00:00 0
| 3ffad400000-3ffad423000 r-xp 00000000 5e:01 133698                       /usr/lib64/ld-2.17.so
| 3ffad424000-3ffad425000 r--p 00023000 5e:01 133698                       /usr/lib64/ld-2.17.so
| 3ffad425000-3ffad426000 rw-p 00024000 5e:01 133698                       /usr/lib64/ld-2.17.so
| 3ffad426000-3ffad427000 rw-p 00000000 00:00 0
| 3ffad473000-3ffad47e000 rw-p 00000000 00:00 0
| 3ffad47e000-3ffad480000 r-xp 00000000 00:00 0                            [vdso]
| 3ffdb181000-3ffdb980000 rw-p 00000000 00:00 0                            [stack]
|
|


Finished tests in 7.935617s, 3.6544 tests/s, 23.9427 assertions/s.
29 tests, 190 assertions, 1 failures, 0 errors, 0 skips

ruby -v: ruby 2.8.0dev (2020-04-12T03:45:22Z master 5c27681813) [s390x-linux]
make: *** [yes-test-all] Error 1
```

The segmentation fault happens in a Ruby script invoked from test_fiber.rb by `EnvUtil.invoke_ruby()`.  The Ruby script is to deliberately cause a stack overflow as follows.

```
$stdout.sync=true; def rec; print "."; 1.times{1.times{1.times{rec}}}; end; Fiber.new{rec}.resume
```
On s390x, this script caused SystemStackError, which I think is expected.  However, it was during the handling of the stack overflow when the segmentation fault happened.

The core dump shows the following stack trace.
```
(gdb) bt
#0  0x000003ffb62c1350 in raise () from /lib64/libc.so.6
#1  0x000003ffb62c2bd8 in abort () from /lib64/libc.so.6
#2  0x000002aa0c84bf9a in die () at error.c:646
#3  rb_bug_for_fatal_signal (default_sighandler=0x0, sig=sig@entry=11,
    ctx=ctx@entry=0x2aa2d18fc50,
    fmt=fmt@entry=0x2aa0c89352c "Segmentation fault at %p") at error.c:678
#4  0x000002aa0c6fbd60 in sigsegv (sig=<optimized out>, info=0x2aa2d18fbd0,
    ctx=0x2aa2d18fc50) at signal.c:955
#5  <signal handler called>
#6  0x000002aa0c5d1f36 in gc_mark_children (
    objspace=objspace@entry=0x2aa2d09c6b0, obj=obj@entry=2929923415200)
    at gc.c:5478
#7  0x000002aa0c5d3ac8 in rgengc_rememberset_mark (heap=0x2aa2d09c6d8,
    objspace=0x2aa2d09c6b0) at gc.c:6747
#8  gc_marks_start (full_mark=<optimized out>, objspace=0x2aa2d09c6b0)
    at gc.c:6314
#9  gc_marks (full_mark=<optimized out>, objspace=0x2aa2d09c6b0) at gc.c:6583
#10 gc_start (objspace=objspace@entry=0x2aa2d09c6b0, reason=<optimized out>,
    reason@entry=256) at gc.c:7370
#11 0x000002aa0c5a9370 in heap_prepare (heap=0x2aa2d09c6d8,
    objspace=<optimized out>) at gc.c:1977
#12 heap_get_freeobj_from_next_freepage (
    objspace=objspace@entry=0x2aa2d09c6b0, heap=heap@entry=0x2aa2d09c6d8)
    at gc.c:1989
---Type <return> to continue, or q <return> to quit---
#13 0x000002aa0c5d7cb0 in heap_get_freeobj (heap=0x2aa2d09c6d8,
    objspace=0x2aa2d09c6b0) at gc.c:2028
#14 newobj_slowpath (wb_protected=1, objspace=0x2aa2d09c6b0, v3=v3@entry=0,
    v2=0, v1=0, flags=5, klass=2929923683840) at gc.c:2170
#15 newobj_slowpath_wb_protected (klass=2929923683840, flags=5, v1=v1@entry=0,
    v2=v2@entry=0, v3=v3@entry=0, objspace=0x2aa2d09c6b0) at gc.c:2182
#16 0x000002aa0c5d817c in newobj_of (wb_protected=1, v3=0, v2=0, v1=0,
    flags=5, klass=<optimized out>) at gc.c:2218
#17 rb_wb_protected_newobj_of (klass=<optimized out>, flags=flags@entry=5)
    at gc.c:2234
#18 0x000002aa0c710fa2 in str_alloc (klass=<optimized out>) at string.c:745
#19 str_new0 (klass=<optimized out>, ptr=0x2aa0c85ad0e "\t", len=1,
    termlen=<optimized out>) at string.c:767
#20 0x000002aa0c5b1f28 in ruby3_str_new_cstr (str=0x2aa0c85ad0e "\t")
    at ./include/ruby/3/intern/string.h:159
#21 print_backtrace (eclass=2929923530680, errat=errat@entry=2929923354920,
    str=str@entry=8, reverse=reverse@entry=0) at eval_error.c:250
#22 0x000002aa0c5b3f68 in print_backtrace (reverse=0, str=8,
    errat=<optimized out>, eclass=<optimized out>) at eval_error.c:233
#23 rb_error_write (reverse=0, highlight=0, str=8, errat=<optimized out>,
    emesg=2929923530600, errinfo=<optimized out>) at eval_error.c:340
#24 rb_ec_error_print (ec=ec@entry=0x2aa2d09cb40, errinfo=<optimized out>)
    at eval_error.c:365
#25 0x000002aa0c5b4572 in error_handle (ec=0x2aa2d09cb40, ex=<optimized out>)
---Type <return> to continue, or q <return> to quit---
    at eval_error.c:478
#26 0x000002aa0c5b4d50 in rb_ec_cleanup (ec=ec@entry=0x2aa2d09cb40,
    ex=<optimized out>) at eval.c:241
#27 0x000002aa0c5b565a in ruby_run_node (n=0x2aa2d0b6128) at eval.c:348
#28 0x000002aa0c5af68a in main (argc=3, argv=0x3ffd127e9e8) at ./main.c:50
```

At gc.c:5478, the segmentation fault happened because `any->as.typeddata.type` was 0.  `as.typeddata.type` should not be 0 for RTypedData.
```
  5473        case T_DATA:
  5474          {
  5475              void *const ptr = DATA_PTR(obj);
  5476              if (ptr) {
  5477                  RUBY_DATA_FUNC mark_func = RTYPEDDATA_P(obj) ?
  5478                      any->as.typeddata.type->function.dmark :
  5479                      any->as.data.dmark;
  5480                  if (mark_func) (*mark_func)(ptr);
  5481              }
  5482          }
  5483          break;
```

This is a timing bug, but it almost always happens with 5c27681813.  It is not clear to which commit this issue is related.  In Ruby CI, it started happening in early February 2020 and stopped showing up after increasing the stack size by `ulimit -s`.  It started happening again in early April 2020 and disappeared on April 15.

Anybody has any ideas how I should debug this?



-- 
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