Re: [Qemu-devel] [PATCH 1/3] colo-compare: serialize compare thread's initialization with main thread

[Hailiang Zhang]

On 2017/4/25 16:41, Jason Wang wrote:
> On 2017年04月24日 14:03, Hailiang Zhang wrote:
> > On 2017/4/24 12:10, Jason Wang wrote:
> > > On 2017年04月20日 15:46, zhanghailiang wrote:
> > > > We call qemu_chr_fe_set_handlers() in colo-compare thread, it is used
> > > > to detach watched fd from default main context, so it has chance to
> > > > handle the same watched fd with main thread concurrently, which will
> > > > trigger an error report:
> > > > "qemu-char.c:918: io_watch_poll_finalize: Assertion `iwp->src ==
> > > > ((void *)0)' failed."
> > > Anyway to prevent fd from being handled by main thread before creating
> > > colo thread? Using semaphore seems not elegant.
> > So how about calling qemu_mutex_lock_iothread() before
> > qemu_chr_fe_set_handlers() ?
> Looks better, but I needs more information e.g how main thread can touch it?

Hmm, this happened quite occasionally, and we didn't catch the first place 
(backtrace)
of removing fd from been watched, but  from the codes logic, we found there 
should
be such possible cases:
tcp_chr_write (Or tcp_chr_read/tcp_chr_sync_read/chr_disconnect)
 ->tcp_chr_disconnect (Or char_socket_finalize)
    ->tcp_chr_free_connection
      -> remove_fd_in_watch(chr);

Anyway, it needs the protection from been freed twice.

Thanks,
Hailiang
> Thanks
>
> .