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authorChristian Krinitsin <mail@krinitsin.com>2025-07-03 19:39:53 +0200
committerChristian Krinitsin <mail@krinitsin.com>2025-07-03 19:39:53 +0200
commitdee4dcba78baf712cab403d47d9db319ab7f95d6 (patch)
tree418478faf06786701a56268672f73d6b0b4eb239 /results/classifier/deepseek-r1:14b/output/hypervisor/650
parent4d9e26c0333abd39bdbd039dcdb30ed429c475ba (diff)
downloademulator-bug-study-dee4dcba78baf712cab403d47d9db319ab7f95d6.tar.gz
emulator-bug-study-dee4dcba78baf712cab403d47d9db319ab7f95d6.zip
restructure results
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+
+Monitor device_add triggers deadlock when calling drain_call_rcu on QEMU >= 6.0.0
+Description of problem:
+It hangs
+Steps to reproduce:
+1. Run the QEMU:
+   ```
+   ./qemu-system-mips64 -nographic
+   ```
+2. Enter into the QEMU monitor: press ctrl-a c
+3. Execute command `device_add` without arguments:
+```
+(qemu) device_add
+```
+4. It hangs so bad that only `kill -9` helps
+Additional information:
+I didn't test versions between 4.2.0 and 6.0.0, but I can confirm that 6.0.0, 6.1.0 and the latest master pull have this bug, while version 4.2.0 doesn't have it.
+
+I've tracked the problem and found this.
+
+1. Command `device_add` calls function `drain_call_rcu`. `drain_call_rcu` waits indefinitely for drain_complete_event.
+2. Function `cpu_exec` in accel/tcg/cpu-exec.c calls `rcu_read_lock` but does not call `rcu_read_unlock()`. `cpu_exec` just spins in its inner loop.
+3. Function `call_rcu_thread` hanged in calling the `synchronize_rcu` which calls `wait_for_readers`.
+
+If I execute `stop` command in QEMU monitor before calling `device_add` command, no hang happen.