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Fix a race condition around mjit_recompile

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This fixes SEGVs like https://github.com/ruby/ruby/runs/2715166621?check_suite_focus=true.

When mjit_recompile is called when mjit_compile is compiling the exact
same iseq (and after it called mjit_capture_cc_entries), iseq->body->jit_unit
is re-created and its cc_entries becomes NULL. Then, when it tries to
lookup cc_entries through iseq->body->jit_unit, it fails.
This commit is contained in:
Takashi Kokubun 2021-06-02 22:07:44 -07:00
parent 007e439fe9
commit 86c262541a
No known key found for this signature in database
GPG Key ID: 6FFC433B12EE23DD
2 changed files with 17 additions and 8 deletions
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21
mjit.c
View File

@ -350,17 +350,22 @@ mjit_recompile(const rb_iseq_t *iseq)
RSTRING_PTR(rb_iseq_path(iseq)), FIX2INT(iseq->body->location.first_lineno));
assert(iseq->body->jit_unit != NULL);
// Lazily move active_units to stale_units to avoid race conditions around active_units with compaction
CRITICAL_SECTION_START(3, "in rb_mjit_recompile_iseq");
iseq->body->jit_unit->stale_p = true;
pending_stale_p = true;
CRITICAL_SECTION_FINISH(3, "in rb_mjit_recompile_iseq");
iseq->body->jit_func = (mjit_func_t)NOT_ADDED_JIT_ISEQ_FUNC;
mjit_add_iseq_to_process(iseq, &iseq->body->jit_unit->compile_info);
if (UNLIKELY(mjit_opts.wait)) {
remove_from_list(iseq->body->jit_unit, &active_units);
add_to_list(iseq->body->jit_unit, &stale_units);
mjit_add_iseq_to_process(iseq, &iseq->body->jit_unit->compile_info);
mjit_wait(iseq->body);
}
else {
// Lazily move active_units to stale_units to avoid race conditions around active_units with compaction.
// Also, it's lazily moved to unit_queue as well because otherwise it won't be added to stale_units properly.
// It's good to avoid a race condition between mjit_add_iseq_to_process and mjit_compile around jit_unit as well.
CRITICAL_SECTION_START(3, "in rb_mjit_recompile_iseq");
iseq->body->jit_unit->stale_p = true;
iseq->body->jit_func = (mjit_func_t)NOT_ADDED_JIT_ISEQ_FUNC;
pending_stale_p = true;
CRITICAL_SECTION_FINISH(3, "in rb_mjit_recompile_iseq");
}
}
// Recompile iseq, disabling send optimization

4
mjit_worker.c
View File

@ -1396,6 +1396,8 @@ unload_units(void)
}
}
static void mjit_add_iseq_to_process(const rb_iseq_t *iseq, const struct rb_mjit_compile_info *compile_info);
// The function implementing a worker. It is executed in a separate
// thread by rb_thread_create_mjit_thread. It compiles precompiled header
// and then compiles requested ISeqs.
@ -1445,6 +1447,8 @@ mjit_worker(void)
unit->stale_p = false;
remove_from_list(unit, &active_units);
add_to_list(unit, &stale_units);
// Lazily put it to unit_queue as well to avoid race conditions on jit_unit with mjit_compile.
mjit_add_iseq_to_process(unit->iseq, &unit->iseq->body->jit_unit->compile_info);
}
}
}