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+<think>
+Okay, so I'm trying to figure out why my QEMU VM is experiencing CPU soft lockups. From the backtrace provided, it looks like when a QMP command like `drive_add` is executed, the main thread holds onto the `qemu_global_mutex` while performing an synchronous operation, such as `pread`. If this operation takes too long due to network latency or high IO pressure, other VCPU threads can't acquire the mutex and get stuck, leading to the soft lockup.
+
+I remember that in QEMU, the main thread handles a lot of critical operations, including device hotplug via commands like `drive_add`. When it performs I/O operations like reading from storage (using `pread`), it's blocking until the data is read. This means if the storage is slow or there's network issues, the main thread won't release the mutex for a long time.
+
+So, how can we prevent the main thread from holding onto the global mutex during these potentially lengthy operations? Maybe the I/O operations should be offloaded to another thread so that the main thread doesn't get blocked. Alternatively, using asynchronous I/O might help since it allows other threads to proceed while waiting for the I/O to complete.
+
+I think about how QEMU handles device hotplug currently. It's done in the main thread because it requires certain state checks and operations that can't be easily moved elsewhere. But maybe there's a way to refactor this so that after receiving the command, the main thread initiates an asynchronous operation and then releases the mutex.
+
+Another thought: perhaps using non-blocking I/O for these operations would help. If `pread` is called in a non-blocking manner, the main thread can proceed without waiting for the I/O to complete, allowing other threads to acquire the mutex and continue execution. However, this might require handling completion callbacks elsewhere, which could complicate things.
+
+I also consider the use of worker threads. Maybe the main thread can kick off an I/O operation on a separate thread and then release the mutex immediately. Once the I/O completes, it notifies the main thread or other workers to proceed with any necessary state updates. This way, the global mutex isn't held during the potentially long wait for I/O.
+
+Looking into QEMU's code structure, I realize that the `qemu_global_mutex` is used to protect various internal states and prevent concurrent modifications from multiple threads. Therefore, any operation that needs to modify these states must hold the mutex. But if holding the mutex while doing synchronous I/O is problematic, maybe we can find a way to offload the I/O part without needing to hold the mutex.
+
+Perhaps introducing asynchronous operations for device hotplug commands could be the solution. For instance, when `drive_add` is called via QMP, instead of performing the I/O synchronously in the main thread, it could schedule an asynchronous task that handles the I/O and updates the state once completed. This would allow the main thread to release the mutex quickly, letting other VCPUs proceed.
+
+I should also think about any existing mechanisms or patches in QEMU related to this issue. Maybe there are ongoing efforts to make certain operations asynchronous. Checking the QEMU bug tracker or mailing lists might reveal similar issues and possible solutions.
+
+In summary, the main problem is that the main thread holds a critical mutex during synchronous I/O operations, which can block other threads for extended periods. To fix this, we need to find ways to either avoid holding the mutex during these operations or offload them to asynchronous tasks so that the main thread remains responsive.
+</think>
+
+To address the CPU soft lockups in QEMU caused by long-running synchronous I/O operations while holding the `qemu_global_mutex`, consider implementing the following solutions:
+
+1. **Asynchronous I/O Operations**:
+   - Refactor device hotplug commands (like `drive_add`) to use asynchronous I/O for operations such as reading from storage or performing `ioctl`. This allows the main thread to release the mutex immediately, preventing VCPUs from being blocked.
+
+2. **Offload Synchronous Operations to Worker Threads**:
+   - Introduce a mechanism where the main thread schedules an asynchronous task upon receiving a QMP command that involves I/O. The task would perform the I/O operation in a separate thread and notify the main thread once completed, thus avoiding holding the mutex during I/O.
+
+3. **Non-blocking I/O for Critical Paths**:
+   - Where feasible, switch to non-blocking I/O calls within the main thread for operations that could block for extended periods. This would allow the main thread to continue processing other tasks while waiting for I/O completion.
+
+4. **Mutex Avoidance During I/O**:
+   - Evaluate if certain parts of the state can be updated without holding the `qemu_global_mutex` or find alternative synchronization mechanisms that don't involve blocking on the mutex during I/O.
+
+5. **Monitoring and Logging**:
+   - Implement monitoring to track the duration of critical operations and identify cases where I/O operations are causing delays. Use this data to optimize performance and ensure timely completion of operations.
+
+By implementing these strategies, the main thread will no longer be a bottleneck, allowing VCPUs to proceed without being blocked by long-running I/O operations, thus preventing CPU soft lockups.
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