Re: [Qemu-devel] [PATCH v2] qemu_mutex_iothread_locked not correctly synchronized

[David Engraf <david.engraf@sysgo.com>]

Am 25.11.2015 um 14:26 schrieb Paolo Bonzini:
>
>
> On 25/11/2015 13:31, David Engraf wrote:
>> Hi Paolo,
>>
>> please check the new version. I removed changing the iothread_locked
>> variable. But I still need to set the correct value of iothread_locked
>> when using qemu_cond_wait.
>
> 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.

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

David