Bug #18816: Ractor segfaulting MacOS 12.4 (aarch64 / M1 processor)

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: ruby 3.1.2p20 (2022-04-12 revision 4491bb740a) [arm64-darwin21]
• Backport: 2.7: UNKNOWN, 3.0: REQUIRED, 3.1: DONE

[brodock (Gabriel Mazetto)]

Reproduction server:

require 'socket'

# Set based on CPU count
CONCURRENCY = 8

server = TCPServer.new(8080)
workers = CONCURRENCY.times.map do
  Ractor.new do
    loop do
      # receive TCPSocket
      session = Ractor.recv

      request = session.gets
      puts request

      session.print "HTTP/1.1 200\r\n"
      session.print "Content-Type: text/html\r\n"
      session.print "\r\n"
      session.print "Hello world! Current time is #{Time.now}"
      session.close
    end
  end
end

loop do
  conn, _ = server.accept

  # pass TCPSocket to one of the workers
  workers.sample.send(conn, move: true)
end

run apache benchmark against code above:

ab -n 20000 -c 20 http://localhost:8080/

---

ractorserver-crash.rb:21: [BUG] Segmentation fault at 0xf94012a9aa1503e8
ruby 3.1.2p20 (2022-04-12 revision 4491bb740a) [arm64-darwin21]

-- Crash Report log information --------------------------------------------
   See Crash Report log file in one of the following locations:
     * ~/Library/Logs/DiagnosticReports
     * /Library/Logs/DiagnosticReports
   for more details.
Don't forget to include the above Crash Report log file in bug reports.

-- Control frame information -----------------------------------------------
c:0005 p:---- s:0019 e:000018 CFUNC  :close
c:0004 p:0074 s:0015 e:000014 BLOCK  ractorserver-crash.rb:21 [FINISH]
c:0003 p:---- s:0010 e:000009 CFUNC  :loop
c:0002 p:0004 s:0006 e:000005 BLOCK  ractorserver-crash.rb:10 [FINISH]
c:0001 p:---- s:0003 e:000002 (none) [FINISH]

-- Ruby level backtrace information ----------------------------------------
ractorserver-crash.rb:10:in `block (2 levels) in <main>'
ractorserver-crash.rb:10:in `loop'
ractorserver-crash.rb:21:in `block (3 levels) in <main>'
ractorserver-crash.rb:21:in `close'

-- Machine register context ------------------------------------------------
  x0: 0x0000000000000000  x1: 0x000000011d009a00  x2: 0x0000000000000000
  x3: 0x0000000000000000  x4: 0x000000016be1a034  x5: 0x0000000000000000
  x6: 0x0000000000000030  x7: 0x000000016be1a050 x18: 0x0000000000000000
 x19: 0x000000016be1a098 x20: 0x000000000000000c x21: 0x000000011d009a00
 x22: 0x0000000104f046a8 x23: 0x000000011d009b60 x24: 0xf94012a9aa1503e8
 x25: 0x0000000000000002 x26: 0x00006000029d66a0 x27: 0x0000000000000000
 x28: 0x0000000055550083  lr: 0x0000000104dddad4  fp: 0x000000016be1a080
  sp: 0x000000016be1a030

-- Other runtime information -----------------------------------------------

* Loaded script: ractorserver-crash.rb

* Loaded features:

    0 enumerator.so
    1 thread.rb
    2 fiber.so
    3 rational.so
    4 complex.so
    5 ruby2_keywords.rb
    6 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/arm64-darwin21/enc/encdb.bundle
    7 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/arm64-darwin21/enc/trans/transdb.bundle
    8 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/arm64-darwin21/rbconfig.rb
    9 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/rubygems/compatibility.rb
   10 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/rubygems/defaults.rb
   11 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/rubygems/deprecate.rb
   12 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/rubygems/errors.rb
   13 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/rubygems/unknown_command_spell_checker.rb
   14 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/rubygems/exceptions.rb
   15 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/rubygems/basic_specification.rb
   16 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/rubygems/stub_specification.rb
   17 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/rubygems/platform.rb
   18 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/rubygems/version.rb
   19 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/rubygems/requirement.rb
   20 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/rubygems/util/list.rb
   21 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/rubygems/specification.rb
   22 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/rubygems/util.rb
   23 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/rubygems/dependency.rb
   24 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/rubygems/core_ext/kernel_gem.rb
   25 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/arm64-darwin21/monitor.bundle
   26 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/monitor.rb
   27 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/rubygems/core_ext/kernel_require.rb
   28 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/rubygems/core_ext/kernel_warn.rb
   29 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/rubygems.rb
   30 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/rubygems/path_support.rb
   31 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/error_highlight/version.rb
   32 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/error_highlight/base.rb
   33 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/error_highlight/formatter.rb
   34 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/error_highlight/core_ext.rb
   35 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/error_highlight.rb
   36 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/did_you_mean/version.rb
   37 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/did_you_mean/core_ext/name_error.rb
   38 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/did_you_mean/levenshtein.rb
   39 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/did_you_mean/jaro_winkler.rb
   40 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/did_you_mean/spell_checker.rb
   41 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/did_you_mean/spell_checkers/name_error_checkers/class_name_checker.rb
   42 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/did_you_mean/spell_checkers/name_error_checkers/variable_name_checker.rb
   43 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/did_you_mean/spell_checkers/name_error_checkers.rb
   44 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/did_you_mean/spell_checkers/method_name_checker.rb
   45 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/did_you_mean/spell_checkers/key_error_checker.rb
   46 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/did_you_mean/spell_checkers/null_checker.rb
   47 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/did_you_mean/tree_spell_checker.rb
   48 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/did_you_mean/spell_checkers/require_path_checker.rb
   49 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/did_you_mean/spell_checkers/pattern_key_name_checker.rb
   50 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/did_you_mean/formatter.rb
   51 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/did_you_mean.rb
   52 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/arm64-darwin21/socket.bundle
   53 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/arm64-darwin21/io/wait.bundle
   54 /Users/brodock/.rvm/rubies/ruby-3.1.2/lib/ruby/3.1.0/socket.rb

* Process memory map:

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1046b0000-1046b4000 --- /usr/lib/dyld
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[IMPORTANT]
Don't forget to include the Crash Report log file under
DiagnosticReports directory in bug reports.

[brodock (Gabriel Mazetto)]

• ruby -v set to ruby 3.1.2p20 (2022-04-12 revision 4491bb740a) [arm64-darwin21]

[tombruijn (Tom de Bruijn)]

• File segfault.txt segfault.txt added

I get the same segfault, but not as consistent as Gabriel. I had to first do a normal request in the browser before running "ab" the couple times it printed the segfault, but I haven't been able to reproduce as consistently. The localhost:8080 server is also unresponsive after running "ab" and I need to kill the process to try again when it doesn't segfault.

Environment details:

• Ruby 3.1.2p20 installed using ruby-install and managed with chruby. (ruby 3.1.2p20 (2022-04-12 revision 4491bb740a) [arm64-darwin21])
• macOS 12.4
• MacBook Pro M1 Pro (14-inch 2021)

Running as:

chruby 3.1.2
ruby app.rb

See attached segfault file of a time that it segfaulted.

[brodock (Gabriel Mazetto)]

I've tried to isolate the problem with a few attempts:

First guess was that something GC related (cleaning up something that was still in use etc).

I've tried to disable GC with code below:

require 'socket'

# Set based on CPU count
CONCURRENCY = 8

GC.disable

server = TCPServer.new(8080)
workers = CONCURRENCY.times.map do
  Ractor.new do
    loop do
      # receive TCPSocket
      session = Ractor.recv

      request = session.gets
      puts request

      session.print "HTTP/1.1 200\r\n"
      session.print "Content-Type: text/html\r\n"
      session.print "\r\n"
      session.print "Hello world! Current time is #{Time.now}"
      session.close
    end
  end
end

loop do
  conn, _ = server.accept

  # pass TCPSocket to one of the workers
  workers.sample.send(conn, move: true)
end

still get segfault.

Then tried to run the same code with 3.1.2 compiled with jemalloc, assuming could be something malloc related, still get a segfault.

[brodock (Gabriel Mazetto)]

I've tried to reproduce the problem in a container running from the M1 mac as host, but it seems the issue is mac-specific, as I couldn't make it SEGV.

Linux ac9a228ca7ac 5.15.40-0-virt #1-Alpine SMP Wed, 18 May 2022 08:12:19 +0000 aarch64 GNU/Linux

using ruby:3.1.2 docker tag (running from containerd using rancher-desktop)

[tenderlovemaking (Aaron Patterson)]

• File 0001-Use-VM-Lock-when-mutating-waiting-threads-list.patch 0001-Use-VM-Lock-when-mutating-waiting-threads-list.patch added

I took a look at this, and it looks like we're missing a lock when deleting the fd from waiting_fds list. I've attached a patch that fixes the crash for me. It seems like not every request gets serviced, but I think that might be a different problem.

I've also sent a pull request on GitHub here: https://github.com/ruby/ruby/pull/6116

[tenderlovemaking (Aaron Patterson)]

• Status changed from Open to Closed

Applied in changeset git|de51bbcb544651fb499dd4cc757a2bf6f3b439cf.

---

Use VM Lock when mutating waiting threads list

rb_thread_wait_for_single_fd needs to mutate the waiting_fds list
that is stored on the VM. We need to delete the FD from the list before
returning, and deleting from the list requires a VM lock (because the
list is a global).

[Bug #18816] [ruby-core:108771]

Co-Authored-By: Alan Wu [e-mail]

[brodock (Gabriel Mazetto)]

Can we backport this to 3.0 and 3.1?

[tenderlovemaking (Aaron Patterson)]

• Backport changed from 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN to 2.7: UNKNOWN, 3.0: REQUIRED, 3.1: REQUIRED

[brodock (Gabriel Mazetto)]

I don't get a ruby segfault anymore. It works fine when using no concurrency:

hey -n 20000 http://localhost:8080/                                                                                                               

Summary:
  Total:	22.5328 secs
  Slowest:	1.8602 secs
  Fastest:	0.0004 secs
  Average:	0.0477 secs
  Requests/sec:	887.5935


Response time histogram:
  0.000 [1]	|
  0.186 [17315]	|■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■
  0.372 [2634]	|■■■■■■
  0.558 [0]	|
  0.744 [0]	|
  0.930 [0]	|
  1.116 [0]	|
  1.302 [0]	|
  1.488 [0]	|
  1.674 [0]	|
  1.860 [50]	|


Latency distribution:
  10% in 0.0021 secs
  25% in 0.0025 secs
  50% in 0.0029 secs
  75% in 0.0036 secs
  90% in 0.3043 secs
  95% in 0.3081 secs
  99% in 0.3132 secs

Details (average, fastest, slowest):
  DNS+dialup:	0.0462 secs, 0.0004 secs, 1.8602 secs
  DNS-lookup:	0.0006 secs, 0.0000 secs, 0.0159 secs
  req write:	0.0001 secs, 0.0000 secs, 0.0052 secs
  resp wait:	0.0012 secs, 0.0000 secs, 0.0118 secs
  resp read:	0.0002 secs, 0.0000 secs, 0.0065 secs

Status code distribution:
  [200]	20000 responses

with -c 20, I get an IOError after a while, which seems to correlate to what you identified as not all requests finishing.

I will open a separate issue for that:

https://bugs.ruby-lang.org/issues/18940

[nagachika (Tomoyuki Chikanaga)]

• Backport changed from 2.7: UNKNOWN, 3.0: REQUIRED, 3.1: REQUIRED to 2.7: UNKNOWN, 3.0: REQUIRED, 3.1: DONE

ruby_3_1 99d254d8b025fd952375ed15c345ecc1b806652a merged revision(s) de51bbcb544651fb499dd4cc757a2bf6f3b439cf.