summary refs log tree commit diff stats
path: root/results/classifier/accel-gemma3:12b/kvm/1195
diff options
context:
space:
mode:
authorChristian Krinitsin <mail@krinitsin.com>2025-07-03 16:27:09 +0000
committerChristian Krinitsin <mail@krinitsin.com>2025-07-03 16:27:09 +0000
commit4d9e26c0333abd39bdbd039dcdb30ed429c475ba (patch)
tree4010d5fb3e8bc48c110a2c1ff2a16b8648cb86bb /results/classifier/accel-gemma3:12b/kvm/1195
parent5541099586dbd6018574cb44e1934907c121526f (diff)
downloadqemu-analysis-4d9e26c0333abd39bdbd039dcdb30ed429c475ba.tar.gz
qemu-analysis-4d9e26c0333abd39bdbd039dcdb30ed429c475ba.zip
add gemma accelerator classification results
Diffstat (limited to 'results/classifier/accel-gemma3:12b/kvm/1195')
-rw-r--r--results/classifier/accel-gemma3:12b/kvm/119519
1 files changed, 19 insertions, 0 deletions
diff --git a/results/classifier/accel-gemma3:12b/kvm/1195 b/results/classifier/accel-gemma3:12b/kvm/1195
new file mode 100644
index 000000000..3f8dc50c9
--- /dev/null
+++ b/results/classifier/accel-gemma3:12b/kvm/1195
@@ -0,0 +1,19 @@
+
+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.