Re: [PATCH v8 13/21] main: keep rcu_atfork callback enabled for qtest

[Thomas Huth <thuth@redhat.com>]

On 29/01/2020 06.34, Bulekov, Alexander wrote:
> The qtest-based fuzzer makes use of forking to reset-state between
> tests. Keep the callback enabled, so the call_rcu thread gets created
> within the child process.
> 
> Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
> ---
>  vl.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/vl.c b/vl.c
> index bb77935f04..cf8e2d3ebb 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -3794,7 +3794,14 @@ void qemu_init(int argc, char **argv, char **envp)
>      set_memory_options(&ram_slots, &maxram_size, machine_class);
>  
>      os_daemonize();
> -    rcu_disable_atfork();
> +
> +    /*
> +     * If QTest is enabled, keep the rcu_atfork enabled, since system processes
> +     * may be forked testing purposes (e.g. fork-server based fuzzing)
> +     */
> +    if (!qtest_enabled()) {
> +        rcu_disable_atfork();
> +    }
>  
>      if (pid_file && !qemu_write_pidfile(pid_file, &err)) {
>          error_reportf_err(err, "cannot create PID file: ");

 Hi Alexander,

I think this patch might maybe not work as expected: The qtest_enabled()
has been added before configure_accelerators() is called in main(). So
qtest_enabled() should always return "false" and thus
rcu_disabled_fork() is still called in any case... could you please
double-check whether it works for you and I just made a mistake, or
whether this is a bug indeed?

 Thanks,
  Thomas