[ruby-core:74717] [Ruby trunk Bug#11922] [PATCH] fix ASYNC BUG race from bootstraptest/test_fork.rb

Issue #11922 has been updated by Yui NARUSE.

Backport changed from 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: REQUIRED to 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: DONE

ruby_2_3 r54426 merged revision(s) 53373.

----------------------------------------
Bug #11922: [PATCH] fix ASYNC BUG race from bootstraptest/test_fork.rb
https://bugs.ruby-lang.org/issues/11922#change-57851

* Author: Eric Wong
* Status: Closed
* Priority: Normal
* Assignee: 
* ruby -v: 
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: DONE
----------------------------------------
~~~
thread_pthread.c (rb_thread_create_timer_thread): fix race

This fixes an occasional [ASYNC BUG] failure in
bootstraptest/test_fork.rb '[ruby-dev:37934]'
which tests fork/pthread_create failure by setting
RLIMIT_NPROC to 1 and triggering EAGAIN on pthread_create
when attempting to recreate the timer thread.

The problem timeline is as follows:

thread 1                           thread 2
---------------------------------------------------------------
rb_thread_create_timer_thread
setup_communication_pipe
                                   rb_thread_wakeup_timer_thread_low
pthread_create fails               pipe looks valid, write!
CLOSE_INVALIDATE (x4)              EBADF -> ASYNC BUG

The checks in rb_thread_wakeup_timer_thread_low only tried to
guarantee proper ordering with native_stop_timer_thread, not
rb_thread_create_timer_thread :x

Now, this should allow rb_thread_create_timer_thread to
synchronize properly with rb_thread_wakeup_timer_thread_low by
delaying the validation marking of the timer_thread_pipe until
we are certain the timer thread is alive.

In this version, rb_thread_wakeup_timer_thread_low becomes a
noop.  Threading is still completely broken with NPROC==1, but
there's not much we can do about it beside warn the user.
We no longer spew a scary [ASYNC BUG] message at them and
dump core on them.

Note: testing this overnight with the [ruby-dev:37934] bit extracted
from bootstraptest/test_fork.rb

	  main = Thread.current
	  Thread.new { sleep 0.01 until main.stop?; Thread.kill main }
	  Process.setrlimit(:NPROC, 1)
	  fork {}

This bug seems easier to reproduce on my weak VM with 32-bit luserspace
(64-bit kernel) VM than more powerful machines.  Even without this
patch, it could take hours to reproduce the race.  I haven't been able
to reproduce this bug at all on my Phenom II machine.

Way too tired to be committing this right now...
~~~


---Files--------------------------------
0001-thread_pthread.c-rb_thread_create_timer_thread-fix-r.patch (2.1 KB)


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