Re: [Qemu-devel] [RFC PATCH for 4.1] linux-user: unparent CPU object before unref

[Peter Maydell <peter.maydell@linaro.org>]

Ccing the QOM maintainers to make sure we have the
QOM lifecycle operations right here...

On Tue, 16 Jul 2019 at 15:02, Alex Bennée <alex.bennee@linaro.org> wrote:
>
> When a CPU object is created it is parented during it's realize stage.
> If we don't unparent before the "final" unref we will never finzalize
> the object leading to a memory leak. For most setups you probably
> won't notice but with anything that creates and destroys a lot of
> threads this will add up. This goes especially for architectures which
> allocate a lot of memory in their CPU structures.
>
> Fixes: https://bugs.launchpad.net/qemu/+bug/1836558
> Cc: 1836558@bugs.launchpad.net
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> ---
>  linux-user/syscall.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 39a37496fed..4c9313fd9d0 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -7183,6 +7183,7 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
>                            NULL, NULL, 0);
>              }
>              thread_cpu = NULL;
> +            object_unparent(OBJECT(cpu));
>              object_unref(OBJECT(cpu));
>              g_free(ts);
>              rcu_unregister_thread();

I think (as I mentioned on IRC) that we also need to unrealize
the CPU object, because target/ppc at least does some freeing
of memory in its unrealize method. I think we do that by
setting the QOM "realize" property back to "false" -- but that
might barf if we try it on a CPU that isn't hotpluggable...

thanks
-- PMM