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<think>
Okay, so I'm trying to figure out whether this issue is a user-mode or system-mode problem. Let's start by understanding what the user is experiencing.
They're running PostgreSQL/Greenplum inside a Docker container using qemu-aarch64-static for cross-architecture emulation. The host is CentOS7 x86_64, and the container is set to run as arm64. They've noticed that their spinlock implementation is causing the database to panic because it's getting stuck. To debug this, they extracted the spinlock code into a test program which also reproduces the issue when run under qemu.
From the output of their test program, it looks like both parent and child processes are trying to acquire the lock, but eventually, they hit a spin timeout. This suggests that the lock isn't being released properly or that some synchronization is failing between the two processes under the emulator.
I know that in user-mode emulation with QEMU, each process runs as a normal user-space program on the host. The emulator translates the instructions from one architecture to another without involving the kernel in a significant way. However, certain operations might not be handled correctly if they rely on specific CPU features or atomic operations that aren't properly emulated.
In their case, the spinlock uses an atomic test-and-set operation. If QEMU's user-mode emulation doesn't handle this correctly, it could cause deadlocks because the lock isn't being set or cleared as expected. Since the same code works on a physical ARM64 server, the issue is likely with how QEMU is emulating the atomic operations.
So, considering that the problem arises from the way the user-mode emulator handles certain instructions (like test-and-set), this points towards it being a user-mode issue rather than something related to system calls or hardware devices, which would fall under system-mode.
</think>
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