Re: [PATCH v3 1/8] migration: Take migration object refcount earlier for threads

[Fabiano Rosas]

Peter Xu <peterx@redhat.com> writes:

> Both migration thread or background snapshot thread will take a refcount of
> the migration object at the entrace of the thread function.
>
> That makes sense, because it protects the object from being freed by the
> main thread in migration_shutdown() later, but it might still race with it
> if the thread is scheduled too late.  Consider the case right after
> pthread_create() happened, VM shuts down with the object released, but
> right after that the migration thread finally got created, referencing
> MigrationState* in the opaque pointer which is already freed.
>
> The only 100% safe way to make sure it won't get freed is taking the
> refcount right before the thread is created, meanwhile when BQL is held.
>
> Signed-off-by: Peter Xu <peterx@redhat.com>

Reviewed-by: Fabiano Rosas <farosas@suse.de>