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author | Koichi Sasada <ko1@atdot.net> | 2023-04-04 03:39:30 +0900 |
---|---|---|
committer | Koichi Sasada <ko1@atdot.net> | 2023-04-04 07:57:51 +0900 |
commit | b2e848193aad70cffd972b15fcc6cbf6be843d94 (patch) | |
tree | 18a64d9aba1b0bebc2f7f213c67c54161927d290 /thread.c | |
parent | 38209ffdca89a497572486034a4e9ed534607057 (diff) |
fix deadlock on `Thread#join`
because of 9720f5ac894566ade2aabcf9adea0a3235de1353
http://rubyci.s3.amazonaws.com/solaris11-sunc/ruby-master/log/20230403T130011Z.fail.html.gz
```
1) Failure:
TestThread#test_signal_at_join [/export/home/chkbuild/chkbuild-sunc/tmp/build/20230403T130011Z/ruby/test/ruby/test_thread.rb:1488]:
Exception raised:
<#<fatal:"No live threads left. Deadlock?\n1 threads, 1 sleeps current:0x00891288 main thread:0x00891288\n* #<Thread:0xfef89a18 sleep_forever>\n rb_thread_t:0x00891288 native:0x00000001 int:0\n \n">>
Backtrace:
-:30:in `join'
-:30:in `block (3 levels) in <main>'
-:21:in `times'
-:21:in `block (2 levels) in <main>'.
```
The mechanism:
* Main thread (M) calls `Thread#join`
* M: calls `sleep_forever()`
* M: set `th->status = THREAD_STOPPED_FOREVER`
* M: do `checkints`
* M: handle a trap handler with `th->status = THREAD_RUNNABLE`
* M: thread switch at the end of the trap handler
* Another thread (T) will process `Thread#kill` by M.
* T: `rb_threadptr_join_list_wakeup()` at the end of T tris to wakeup M,
but M's state is runnable because M is handling trap handler and
just ignore the waking up and terminate T$a
* T: switch to M.
* M: after the trap handler, reset `th->status = THREAD_STOPPED_FOREVER`
and check deadlock -> Deadlock because only M is living.
To avoid such situation, add new sleep flags `SLEEP_ALLOW_SPURIOUS`
and `SLEEP_NO_CHECKINTS` to skip any check ints.
BTW this is instentional to leave second `vm_check_ints_blocking()`
without checking `SLEEP_NO_CHECKINTS` because `SLEEP_ALLOW_SPURIOUS`
should be specified with `SLEEP_NO_CHECKINTS` and skipping this
checkints can skip any interrupts.
Notes
Notes:
Merged: https://github.com/ruby/ruby/pull/7647
Diffstat (limited to 'thread.c')
-rw-r--r-- | thread.c | 12 |
1 files changed, 10 insertions, 2 deletions
@@ -132,6 +132,8 @@ rb_thread_local_storage(VALUE thread) enum SLEEP_FLAGS { SLEEP_DEADLOCKABLE = 0x01, SLEEP_SPURIOUS_CHECK = 0x02, + SLEEP_ALLOW_SPURIOUS = 0x04, + SLEEP_NO_CHECKINTS = 0x08, }; static void sleep_forever(rb_thread_t *th, unsigned int fl); @@ -418,6 +420,7 @@ rb_threadptr_join_list_wakeup(rb_thread_t *thread) case THREAD_STOPPED: case THREAD_STOPPED_FOREVER: target_thread->status = THREAD_RUNNABLE; + break; default: break; } @@ -1053,7 +1056,7 @@ thread_join_sleep(VALUE arg) rb_fiber_scheduler_block(scheduler, target_th->self, p->timeout); } else if (!limit) { - sleep_forever(th, SLEEP_DEADLOCKABLE); + sleep_forever(th, SLEEP_DEADLOCKABLE | SLEEP_ALLOW_SPURIOUS | SLEEP_NO_CHECKINTS); } else { if (hrtime_update_expire(limit, end)) { @@ -1338,7 +1341,9 @@ sleep_forever(rb_thread_t *th, unsigned int fl) status = fl & SLEEP_DEADLOCKABLE ? THREAD_STOPPED_FOREVER : THREAD_STOPPED; th->status = status; - RUBY_VM_CHECK_INTS_BLOCKING(th->ec); + + if (!(fl & SLEEP_NO_CHECKINTS)) RUBY_VM_CHECK_INTS_BLOCKING(th->ec); + while (th->status == status) { if (fl & SLEEP_DEADLOCKABLE) { rb_ractor_sleeper_threads_inc(th->ractor); @@ -1350,6 +1355,9 @@ sleep_forever(rb_thread_t *th, unsigned int fl) if (fl & SLEEP_DEADLOCKABLE) { rb_ractor_sleeper_threads_dec(th->ractor); } + if (fl & SLEEP_ALLOW_SPURIOUS) { + break; + } woke = vm_check_ints_blocking(th->ec); |