Hi. Before I take the time to prepare a detailed bug report, I wanted to ask whether I'm doing something that is expected to work, or expected not to work.
I am a developer of the LinuxCNC, Free and Open Source software for control of milling machines, lathes, and so forth. Our software uses an IPC model where multiple processes share a memory-mapped region which contains data as well as mutexes to manipulate the data (using gcc intrinsics like __sync_fetch_and_or). On real multiprocessor ARM systems, our testsuite passes, but when running in a debian schroot using qemu-arm-static it regularly deadlocks, apparently with two processes both trying to take the same mutex in a shared memory region. >From what I have been able to tell, the emulation of atomics in qemu is based on a single-process, multi-thread model (based on start_exclusive() in linux-user/main.c, http://git.qemu.org/?p=qemu.git;a=blob;f=linux-user/main.c;h=95ed11d85c1#l160) so right now I think that our code is expected not to work on qemu-user. If that's the case, for our purposes I will simply document that while our software can be built in a qemu-user environment, it cannot be used and its testsuite experiences spurious failures. Thanks for your time, Jeff
