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Diffstat (limited to 'results/classifier/zero-shot/105/instruction/1195')
| -rw-r--r-- | results/classifier/zero-shot/105/instruction/1195 | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/results/classifier/zero-shot/105/instruction/1195 b/results/classifier/zero-shot/105/instruction/1195 new file mode 100644 index 000000000..ee7d37720 --- /dev/null +++ b/results/classifier/zero-shot/105/instruction/1195 @@ -0,0 +1,31 @@ +instruction: 0.789 +graphic: 0.706 +device: 0.695 +other: 0.509 +semantic: 0.459 +mistranslation: 0.340 +network: 0.270 +assembly: 0.232 +boot: 0.197 +socket: 0.193 +vnc: 0.148 +KVM: 0.137 + +Race condition during QEMU exit cleanup can lead to deadlock +Description of problem: +During the cleanup phase of QEMU exiting, there is a small race condition window that can lead QEMU to lock up completely: +In the main QEMU thread, during the exit, the thread will execute the 'qemu_cleanup' function, which calls 'do_vm_stop', which calls 'pause_all_vcpus'. This method tries to (as the name suggests) stop/pause all the vcpu threads. At the same time, the vcpu thread might have just existed it's main mttcg exec loop, which means it will enter 'qemu_wait_io_event'. At this point, the following race condition can occur: +- vcpu_thread - cpus.c:416 <= enters qemu_wait_io_event +- shutdown_thread - cpus.c:555 <= enters pause_all_vcpus +- vcpu_thread - cpus.c:418 <= cpu_thread_is_idle returns true, cpu->stop not set yet +- shutdown_thread - cpus.c:560/561 <= sets cpu->stop and kicks the vcpu, but it's not waiting on cpu->halt_cond yet, so nothing happens +- vcpu_thread - cpus.c:423 <= starts waiting on cpu->halt_cond +- shutdown_thread - cpus.c:570 <= not all vcpus paused, so enters while loop +- shutdown_thread - cpus.c:571 <= starts waiting on qemu_pause_cond +- **deadlock** + +In my case, my plugin registers qemu_plugin_vcpu_idle_cb, so the race window is extended significantly in the vcpu thread (cpus.c:421) but I believe it can happen with the smaller race window as well. + +Note that this explanation is just based on my understanding of the code, and the final state of QEMU during the deadlock after I attached: The main thread (thread 1) was waiting on qemu_pause_cond in pause_all_vcpus, and the vcpu was waiting on cpu->halt_cond in qemu_wait_io_event, with no one else to wake either of them up. (This was following an exit that was triggered by a timeout signal) +Steps to reproduce: +This is a race condition, so I don't have a reliable reproducer. |