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[debugger] skip suspend for unattached threads (mono#18110)
[2019-12] [debugger] skip suspend for unattached threads When the debugger tries to suspend all the VM threads, it can happen with cooperative-suspend that it tries to suspend a thread that has previously been attached, but then did a "light" detach (that only unsets the domain). With the domain set to `NULL`, looking up a JitInfo for a given `ip` will result into a crash, but it isn't even necessarily needed for the purpose of suspending a thread. More details: Consider the following: ``` (lldb) c error: Process is running. Use 'process interrupt' to pause execution. Process 12832 stopped * thread #9, name = 'tid_a31f', queue = 'NSOperationQueue 0x8069b670 (QOS: UTILITY)', stop reason = breakpoint 1.1 frame #0: 0x00222870 WatchWCSessionAppWatchOSExtension`debugger_interrupt_critical(info=0x81365400, user_data=0xb04dc718) at debugger-agent.c:2716:6 2713 MonoDomain *domain = (MonoDomain *) mono_thread_info_get_suspend_state (info)->unwind_data [MONO_UNWIND_DATA_DOMAIN]; 2714 if (!domain) { 2715 /* not attached */ -> 2716 ji = NULL; 2717 } else { 2718 ji = mono_jit_info_table_find_internal ( domain, MONO_CONTEXT_GET_IP (&mono_thread_info_get_suspend_state (info)->ctx), TRUE, TRUE); 2719 } Target 0: (WatchWCSessionAppWatchOSExtension) stopped. (lldb) bt * thread #9, name = 'tid_a31f', queue = 'NSOperationQueue 0x8069b670 (QOS: UTILITY)', stop reason = breakpoint 1.1 * frame #0: 0x00222870 WatchWCSessionAppWatchOSExtension`debugger_interrupt_critical(info=0x81365400, user_data=0xb04dc718) at debugger-agent.c:2716:6 frame #1: 0x004e177b WatchWCSessionAppWatchOSExtension`mono_thread_info_safe_suspend_and_run(id=0xb0767000, interrupt_kernel=0, callback=(WatchWCSessionAppWatchOSExtension`debugger_interrupt_critical at debugger-agent.c:2708), user_data=0xb04dc718) at mono-threads.c:1358:19 frame #2: 0x00222799 WatchWCSessionAppWatchOSExtension`notify_thread(key=0x03994508, value=0x81378c00, user_data=0x00000000) at debugger-agent.c:2747:2 frame #3: 0x00355bd8 WatchWCSessionAppWatchOSExtension`mono_g_hash_table_foreach(hash=0x8007b4e0, func=(WatchWCSessionAppWatchOSExtension`notify_thread at debugger-agent.c:2733), user_data=0x00000000) at mono-hash.c:310:4 frame #4: 0x0021e955 WatchWCSessionAppWatchOSExtension`suspend_vm at debugger-agent.c:2844:3 frame #5: 0x00225ff0 WatchWCSessionAppWatchOSExtension`process_event(event=EVENT_KIND_THREAD_START, arg=0x039945d0, il_offset=0, ctx=0x00000000, events=0x805b28e0, suspend_policy=2) at debugger-agent.c:4012:3 frame #6: 0x00227c7c WatchWCSessionAppWatchOSExtension`process_profiler_event(event=EVENT_KIND_THREAD_START, arg=0x039945d0) at debugger-agent.c:4072:2 frame #7: 0x0021b174 WatchWCSessionAppWatchOSExtension`thread_startup(prof=0x00000000, tid=2957889536) at debugger-agent.c:4149:2 frame #8: 0x0037912d WatchWCSessionAppWatchOSExtension`mono_profiler_raise_thread_started(tid=2957889536) at profiler-events.h:103:1 frame #9: 0x003d53da WatchWCSessionAppWatchOSExtension`fire_attach_profiler_events(tid=0xb04dd000) at threads.c:1120:2 frame #10: 0x003d4d83 WatchWCSessionAppWatchOSExtension`mono_thread_attach(domain=0x801750a0) at threads.c:1547:2 frame #11: 0x003df1a1 WatchWCSessionAppWatchOSExtension`mono_threads_attach_coop_internal(domain=0x801750a0, cookie=0xb04dcc0c, stackdata=0xb04dcba8) at threads.c:6008:3 frame #12: 0x003df287 WatchWCSessionAppWatchOSExtension`mono_threads_attach_coop(domain=0x00000000, dummy=0xb04dcc0c) at threads.c:6045:9 frame #13: 0x005034b8 WatchWCSessionAppWatchOSExtension`::xamarin_switch_gchandle(self=0x80762c20, to_weak=false) at runtime.m:1805:2 frame #14: 0x005065c1 WatchWCSessionAppWatchOSExtension`::xamarin_retain_trampoline(self=0x80762c20, sel="retain") at trampolines.m:693:2 frame #15: 0x657ea520 libobjc.A.dylib`objc_retain + 64 frame #16: 0x4b4d9caa WatchConnectivity`__66-[WCSession onqueue_handleDictionaryMessageRequest:withPairingID:]_block_invoke + 279 frame #17: 0x453c7df7 Foundation`__NSBLOCKOPERATION_IS_CALLING_OUT_TO_A_BLOCK__ + 12 frame #18: 0x453c7cf4 Foundation`-[NSBlockOperation main] + 88 frame #19: 0x453cacee Foundation`__NSOPERATION_IS_INVOKING_MAIN__ + 27 frame #20: 0x453c6ebd Foundation`-[NSOperation start] + 835 frame #21: 0x453cb606 Foundation`__NSOPERATIONQUEUE_IS_STARTING_AN_OPERATION__ + 27 frame #22: 0x453cb12e Foundation`__NSOQSchedule_f + 194 frame #23: 0x453cb26e Foundation`____addOperations_block_invoke_4 + 20 frame #24: 0x65de007b libdispatch.dylib`_dispatch_call_block_and_release + 15 frame #25: 0x65de126f libdispatch.dylib`_dispatch_client_callout + 14 frame #26: 0x65de3788 libdispatch.dylib`_dispatch_continuation_pop + 421 frame #27: 0x65de2ee3 libdispatch.dylib`_dispatch_async_redirect_invoke + 818 frame #28: 0x65df087d libdispatch.dylib`_dispatch_root_queue_drain + 354 frame #29: 0x65df0ff3 libdispatch.dylib`_dispatch_worker_thread2 + 109 frame #30: 0x66024fa0 libsystem_pthread.dylib`_pthread_wqthread + 208 frame #31: 0x66024e44 libsystem_pthread.dylib`start_wqthread + 36 ``` Going further, `info` is about this thread: ``` (lldb) p/x *(int *)(((char *) info->node.key) + 0xa0) (int) $2 = 0x01243f93 (lldb) thread list Process 12832 stopped thread #1: tid = 0x1243ee1, 0x65f7e396 libsystem_kernel.dylib`mach_msg_trap + 10, name = 'tid_303', queue = 'com.apple.main-thread' thread #2: tid = 0x1243ee6, 0x65f816e2 libsystem_kernel.dylib`__recvfrom + 10 thread #3: tid = 0x1243ee7, 0x65f81aea libsystem_kernel.dylib`__psynch_cvwait + 10, name = 'SGen worker' thread #4: tid = 0x1243ee9, 0x65f7e3d2 libsystem_kernel.dylib`semaphore_wait_trap + 10, name = 'Finalizer' thread #5: tid = 0x1243eea, 0x65f816e2 libsystem_kernel.dylib`__recvfrom + 10, name = 'Debugger agent' thread #6: tid = 0x1243f1d, 0x65f7e396 libsystem_kernel.dylib`mach_msg_trap + 10, name = 'com.apple.uikit.eventfetch-thread' thread #8: tid = 0x1243f93, 0x65f7e396 libsystem_kernel.dylib`mach_msg_trap + 10, name = 'tid_6d0f', queue = 'NSOperationQueue 0x8069b300 (QOS: UTILITY)' * thread #9: tid = 0x12443a9, 0x00222870 WatchWCSessionAppWatchOSExtension`debugger_interrupt_critical(info=0x81365400, user_data=0xb04dc718) at debugger-agent.c:2716:6, name = 'tid_a31f', queue = 'NSOperationQueue 0x8069b670 (QOS: UTILITY)', stop reason = breakpoint 1.1 thread #10: tid = 0x1244581, 0x65f7fd32 libsystem_kernel.dylib`__workq_kernreturn + 10 (lldb) thread select 8 * thread #8, name = 'tid_6d0f', queue = 'NSOperationQueue 0x8069b300 (QOS: UTILITY)' frame #0: 0x65f7e396 libsystem_kernel.dylib`mach_msg_trap + 10 libsystem_kernel.dylib`mach_msg_trap: -> 0x65f7e396 <+10>: retl 0x65f7e397 <+11>: nop libsystem_kernel.dylib`mach_msg_overwrite_trap: 0x65f7e398 <+0>: movl $0xffffffe0, %eax ; imm = 0xFFFFFFE0 0x65f7e39d <+5>: calll 0x65f85f44 ; _sysenter_trap (lldb) bt * thread #8, name = 'tid_6d0f', queue = 'NSOperationQueue 0x8069b300 (QOS: UTILITY)' * frame #0: 0x65f7e396 libsystem_kernel.dylib`mach_msg_trap + 10 frame #1: 0x65f7e8ff libsystem_kernel.dylib`mach_msg + 47 frame #2: 0x66079679 libxpc.dylib`_xpc_send_serializer + 104 frame #3: 0x660794da libxpc.dylib`_xpc_pipe_simpleroutine + 80 frame #4: 0x66079852 libxpc.dylib`xpc_pipe_simpleroutine + 43 frame #5: 0x66043a8f libsystem_trace.dylib`___os_activity_stream_reflect_block_invoke_2 + 30 frame #6: 0x65de126f libdispatch.dylib`_dispatch_client_callout + 14 frame #7: 0x65de3d71 libdispatch.dylib`_dispatch_block_invoke_direct + 257 frame #8: 0x65de3c62 libdispatch.dylib`dispatch_block_perform + 112 frame #9: 0x6604349a libsystem_trace.dylib`_os_activity_stream_reflect + 725 frame #10: 0x6604ef19 libsystem_trace.dylib`_os_log_impl_stream + 468 frame #11: 0x6604e44d libsystem_trace.dylib`_os_log_impl_flatten_and_send + 6410 frame #12: 0x6604cb3b libsystem_trace.dylib`_os_log + 137 frame #13: 0x6604f4aa libsystem_trace.dylib`_os_log_impl + 31 frame #14: 0x4b4eb4e9 WatchConnectivity`WCSerializePayloadDictionary + 393 frame #15: 0x4b4d7c4d WatchConnectivity`-[WCSession onqueue_sendResponseDictionary:identifier:] + 195 frame #16: 0x4b4da435 WatchConnectivity`__66-[WCSession onqueue_handleDictionaryMessageRequest:withPairingID:]_block_invoke.411 + 35 frame #17: 0x453c7df7 Foundation`__NSBLOCKOPERATION_IS_CALLING_OUT_TO_A_BLOCK__ + 12 frame #18: 0x453c7cf4 Foundation`-[NSBlockOperation main] + 88 frame #19: 0x453cacee Foundation`__NSOPERATION_IS_INVOKING_MAIN__ + 27 frame #20: 0x453c6ebd Foundation`-[NSOperation start] + 835 frame #21: 0x453cb606 Foundation`__NSOPERATIONQUEUE_IS_STARTING_AN_OPERATION__ + 27 frame #22: 0x453cb12e Foundation`__NSOQSchedule_f + 194 frame #23: 0x453cb067 Foundation`____addOperations_block_invoke_2 + 20 frame #24: 0x65dedf49 libdispatch.dylib`_dispatch_block_async_invoke2 + 77 frame #25: 0x65de4461 libdispatch.dylib`_dispatch_block_async_invoke_and_release + 17 frame #26: 0x65de126f libdispatch.dylib`_dispatch_client_callout + 14 frame #27: 0x65de3788 libdispatch.dylib`_dispatch_continuation_pop + 421 frame #28: 0x65de2ee3 libdispatch.dylib`_dispatch_async_redirect_invoke + 818 frame #29: 0x65df087d libdispatch.dylib`_dispatch_root_queue_drain + 354 frame #30: 0x65df0ff3 libdispatch.dylib`_dispatch_worker_thread2 + 109 frame #31: 0x66024fa0 libsystem_pthread.dylib`_pthread_wqthread + 208 frame mono#32: 0x66024e44 libsystem_pthread.dylib`start_wqthread + 36 ``` which is a thread in a "light" detach state (aka. coop detach), where we only unset the domain: https://github.com/mono/mono/blob/4cefdcb7ce2d939ee78fb45d1b4913eb3bc064fd/mono/metadata/threads.c#L6084-L6111 Fixes mono#17926 <!-- Thank you for your Pull Request! If you are new to contributing to Mono, please try to do your best at conforming to our coding guidelines http://www.mono-project.com/community/contributing/coding-guidelines/ but don't worry if you get something wrong. One of the project members will help you to get things landed. Does your pull request fix any of the existing issues? Please use the following format: Fixes #issue-number --> Backport of mono#18105. /cc @lewurm
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