Re: [Qemu-devel] [Qemu-stable] Recent patches for 2.4

[Paolo Bonzini <pbonzini@redhat.com>]

On 04/08/2015 11:22, Peter Lieven wrote:
>>>>> edec47c main-loop: fix qemu_notify_event for aio_notify optimization
>>>> Part of the above AioContext series.
>>> So either the whole series or none of them I guess?
>> It's a separate bug, and theoretically it's there in 2.3.1 as well, but
>> no one ever reproduced it (it would hang in make check) so not
>> worthwhile.
> 
> Can you give me a pointer what the symtoms where?

If a thread tries to wake up the main thread using qemu_notify_event(),
the main thread will never wake up.  This for example could happen if
the first thread calls qemu_set_fd_handler() or timer_mod().

> I have a qemu-img convert job on x86_64 that reproducibly hangs on
> bdrv_drain_all at the end of the convert process.
> I convert from nfs:// to local storage here. I try to figure out which BS
> reports busy. Qemu here is still 2.2.1.

qemu-img does not use main-loop, so this cannot be the cause.

The AioContext bugs only happen when you have a thread executing the
main loop and one thread executing aio_poll, so they can also be
excluded as the cause of qemu-img problems.

Paolo