From: ko1@atdot.net
To: ruby-core@ruby-lang.org
Subject: [ruby-core:92541] [Ruby trunk Bug#15821] ruby_process_options() may cause "WB miss (O->Y)"
Date: Sun, 05 May 2019 04:25:54 +0000 (UTC) [thread overview]
Message-ID: <redmine.journal-77900.20190505042554.bf5a4b4b538c6e6f@ruby-lang.org> (raw)
In-Reply-To: redmine.issue-15821.20190504054225@ruby-lang.org
Issue #15821 has been updated by ko1 (Koichi Sasada).
I didn't understand completely, but it is local problem on it? or all of `rb_ary_replace()` calls have the same issue?
----------------------------------------
Bug #15821: ruby_process_options() may cause "WB miss (O->Y)"
https://bugs.ruby-lang.org/issues/15821#change-77900
* Author: wanabe (_ wanabe)
* Status: Open
* Priority: Normal
* Assignee:
* Target version:
* ruby -v: ruby 2.7.0dev (2019-05-04 trunk b72623012d) [x86_64-linux]
* Backport: 2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: UNKNOWN
----------------------------------------
## Problem
Ruby interpreter may cause error "WB miss (O->Y)" on some conditions that are `RGENGC_CHECK_MODE=5` and `RUBY_DEBUG=gc_stress`
## How to reproduce
1. build ruby with high RGENGC_CHECK_MODE
* `make ruby optflags="-O3 -DRGENGC_CHECK_MODE=5"`
2. run ruby with gc_stress
* `RUBY_DEBUG=gc_stress ./ruby --disable-gems -ve 1`
## Probable cause
1. `rb_construct_expanded_load_path` calls `rb_ary_replace(vm->load_path_snapshot, vm->load_path)`.
2. It creates shared root array and makes `vm->load_path` SHARED_ARRAY.
3. After a while, `process_options` calls `RARRAY_ASET(load_path, i, path)`.
4. It calls `rb_gc_writebarrier` -> `gc_writebarrier_generational`.
* Incremental mark phase is finished because of `RUBY_DEBUG=gc_stress`.
5. It makes `vm->load_path` remembered, but not shared root array!
6. "WB miss (O->Y)" is done.
* Old parent is shared root array.
* New child is `path` of above 3.
## Proposal
How about call `rb_ary_modify` before `RARRAY_SET` in `process_options`?
Or using `rb_ary_store` instead of `RARRAY_SET` may avoid the error.
## Sample output
An example of full output is attached.
(Sorry, I GZipped it because of file-size limitation)
The snippet is here:
```
ruby 2.7.0dev (2019-05-04 trunk b72623012d) [x86_64-linux]
verify_internal_consistency_reachable_i: WB miss (O->Y) 0x000055c3262f3610 [3LM ] T_ARRAY [ ] len: 20, capa:2 ptr:0x000055c326498380 -> 0x000055c3262f3908 [2 P ] T_STRING (String) /home/wanabe/.rbenv/versions/trunk/lib/ruby/site_ruby/2.7.0
[all refs] (size: 5307)
(snip)
[allrefs_dump_i] 0x000055c3263349f8 [3LMP ] T_ARRAY [E ] len: 0 (embed) <- <0x000055c326336f28 [0 P U] VM/thread (Thread) VM/thread>
./ruby: [BUG] Segmentation fault at 0x0000000000000010
ruby 2.7.0dev (2019-05-04 trunk b72623012d) [x86_64-linux]
-- Control frame information -----------------------------------------------
c:0001 p:0000 s:0003 E:0022c0 (none) [FINISH]
-- Machine register context ------------------------------------------------
RIP: 0x000055c32452e15a RBP: 0x0000000000000001 RSP: 0x00007ffea126d470
RAX: 0x0000000000000000 RBX: 0x000055c3262ef3c8 RCX: 0x0000000000000001
RDX: 0x000055c324773446 RDI: 0x00007ff8c77cb680 RSI: 0x0000000000000001
R8: 0x000055c3262ef3b8 R9: 0x0000000000000018 R10: 0x0000000000000018
R11: 0x0000000000000246 R12: 0x0000000000000100 R13: 0x0000000000000005
R14: 0x000055c3262f3c28 R15: 0x000055c3262ef1b0 EFL: 0x0000000000010206
-- C level backtrace information -------------------------------------------
/home/wanabe/work/prog/ruby/ruby/tmp/trunk/ruby(rb_vm_bugreport+0x554) [0x55c324769fa4] ../../vm_dump.c:715
[0x55c324760088]
/home/wanabe/work/prog/ruby/ruby/tmp/trunk/ruby(sigsegv+0x42) [0x55c324640d42] ../../signal.c:997
/lib/x86_64-linux-gnu/libpthread.so.0(__restore_rt+0x0) [0x7ff8c797ff40]
/home/wanabe/work/prog/ruby/ruby/tmp/trunk/ruby(allrefs_dump+0x1a) [0x55c32452e15a] /usr/include/x86_64-linux-gnu/bits/stdio2.h:100
[0x55c32453a478]
[0x55c32453a64c]
[0x55c32453f874]
/home/wanabe/work/prog/ruby/ruby/tmp/trunk/ruby(rb_str_dup+0x29) [0x55c32465aa59] ../../string.c:722
[0x55c32463f2e1]
/home/wanabe/work/prog/ruby/ruby/tmp/trunk/ruby(ruby_process_options+0xc0) [0x55c3246404a0] ../../ruby.c:2380
/home/wanabe/work/prog/ruby/ruby/tmp/trunk/ruby(ruby_options+0xca) [0x55c32451e1ea] ../../eval.c:118
/home/wanabe/work/prog/ruby/ruby/tmp/trunk/ruby(main+0x67) [0x55c324519ec7] ../../main.c:42
(snip)
Aborted (core dumped)
```
---Files--------------------------------
out.log.gz (114 KB)
--
https://bugs.ruby-lang.org/
next prev parent reply other threads:[~2019-05-05 4:26 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <redmine.issue-15821.20190504054225@ruby-lang.org>
2019-05-04 5:42 ` [ruby-core:92537] [Ruby trunk Bug#15821] ruby_process_options() may cause "WB miss (O->Y)" s.wanabe
2019-05-05 4:25 ` ko1 [this message]
2019-05-05 9:58 ` [ruby-core:92548] " lourens
2019-05-05 10:38 ` [ruby-core:92550] " s.wanabe
2019-05-21 13:56 ` [ruby-core:92744] " nobu
2019-05-22 8:35 ` [ruby-core:92774] " ko1
2019-07-31 14:32 ` [ruby-core:94076] [Ruby master " nagachika00
2019-08-26 15:02 ` [ruby-core:94569] " usa
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