Am 25.11.2015 um 15:36 schrieb Paolo Bonzini:
On 25/11/2015 15:04, David Engraf wrote:
No, you don't. Who is reading iothread_locked during
qemu_cond_wait_iothread? No one, because it is a thread-local variable
whose address is never taken.
prepare_mmio_access is reading iothread_locked by using
qemu_mutex_iothread_locked after qemu_tcg_wait_io_event calls
qemu_cond_wait. All one the same thread.
Sure, but who has set iothread_locked to false during the execution of
qemu_cond_wait? No one, because it's a thread-local variable. If it's
true before qemu_cond_wait, it will be true after qemu_cond_wait and you
don't need qemu_cond_wait_iothread... unless your compiler is broken and
doesn't generate TLS properly.
Indeed, TLS handling is broken. The address of iothread_locked is always
the same between threads and I can see that a different thread sets
iothread_locked to false, thus my current thread uses an invalid state.
I will have to check why my compiler produces invalid TLS code.
David
Can you compile cpus.c with -S and attach it?
Paolo
qemu_tcg_cpu_thread_fn
-> qemu_tcg_wait_io_event
-> qemu_cond_wait acquires the mutex
qemu_tcg_cpu_thread_fn
-> tcg_exec_all -> tcg_cpu_exec -> cpu_exec
-> cpu_exec ends up in calling prepare_mmio_access