Bug #15360: "ThreadError: deadlock; recursive locking" error when recursive lock shouldn't be possible

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: ruby 2.5.3p105 (2018-10-18 revision 65156) [x86_64-darwin17]
• Backport: 2.4: DONTNEED, 2.5: DONE, 2.6: DONE

[brockspratlen (Brock Spratlen)]

I think I've discovered a Ruby bug, possibly introduced in 2.5.

I've attached a reproduction script; running it on Ruby 2.5.0+ (including previews of 2.6.0) seems to always produce a flood of printed ThreadError: deadlock; recursive locking exceptions, even though the reproduction code doesn't appear to do any recursive locking.

Running the same script on Ruby 2.4.5 doesn't produce any ThreadError: deadlock; recursive locking exceptions. I've run the script several times on Ruby 2.4.5, I simply can't reproduce the raising of ThreadError: deadlock; recursive locking with this script on 2.4.5.

Curiously, removing the puts e.class on line 24 causes the bug to go away: ThreadError: deadlock; recursive locking never gets raised regardless of which Ruby version I'm running. Given this oddity, I can't help but think the issue is something around writing to stdout. This change in particular looks suspect: https://bugs.ruby-lang.org/issues/9323

Thank you!
Brock

[brockspratlen (Brock Spratlen)]

• ruby -v changed from 2.5.3 to ruby 2.5.3p105 (2018-10-18 revision 65156) [x86_64-darwin17]

[brockspratlen (Brock Spratlen)]

• Description updated (diff)

Is there a plan to fix this? We have been noticing this bug occasionally in production.

[wanabe (_ wanabe)]

git bisect shows the problem occurs frequently since r58604.
But I don't know it can occur before the commit.

https://bugs.ruby-lang.org/projects/ruby-trunk/repository/trunk/revisions/66489/entry/thread_sync.c#L267
do_mutex_lock() releases GVL with native_sleep(th, timeout).
The mutex may be released and the thread may be interrupted around the same time.
If so, RUBY_VM_CHECK_INTS_BLOCKING(th->ec) will raise an exception, after locking mutex.

[nbh (nbh _)]

https://github.com/ruby/ruby/pull/2131

[jeremyevans0 (Jeremy Evans)]

• Related to Bug #15508: Mutex recursive lock error when combined with Thread#raise added

[jeremyevans0 (Jeremy Evans)]

• Related to Bug #15645: It is possible to escape `Mutex#synchronize` without releasing the mutex added

[jeremyevans0 (Jeremy Evans)]

• Status changed from Open to Closed
• Backport changed from 2.4: UNKNOWN, 2.5: UNKNOWN to 2.4: DONTNEED, 2.5: REQUIRED, 2.6: REQUIRED

Fix committed at c1d78a7f0ece2004822193a0c1f1fd3dc38c2fdf

[nagachika (Tomoyuki Chikanaga)]

• Backport changed from 2.4: DONTNEED, 2.5: REQUIRED, 2.6: REQUIRED to 2.4: DONTNEED, 2.5: REQUIRED, 2.6: DONE

ruby_2_6 r67728 merged revision(s) c1d78a7f0ece2004822193a0c1f1fd3dc38c2fdf.

[usa (Usaku NAKAMURA)]

• Backport changed from 2.4: DONTNEED, 2.5: REQUIRED, 2.6: DONE to 2.4: DONTNEED, 2.5: DONE, 2.6: DONE

ruby_2_5 r67764 merged revision(s) c1d78a7f0ece2004822193a0c1f1fd3dc38c2fdf.