Re: [PATCH 3/3] rcu: Avoid double rcu frees

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

On Mon, 29 Sept 2025 at 20:08, Peter Xu <peterx@redhat.com> wrote:
>
> Trap call_rcu1() to make sure it won't be invoked twice for one rcu head.
>
> Suggested-by: Peter Maydell <peter.maydell@linaro.org>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  util/rcu.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/util/rcu.c b/util/rcu.c
> index b703c86f15..9272fe5796 100644
> --- a/util/rcu.c
> +++ b/util/rcu.c
> @@ -307,6 +307,8 @@ static void *call_rcu_thread(void *opaque)
>
>  void call_rcu1(struct rcu_head *node, void (*func)(struct rcu_head *node))
>  {
> +    /* Avoid double rcu frees */

I would maybe have this say "Catch accidental attempts to
use the same rcu node for two things at once", which
isn't the same as a "double free" in the usual sense.

> +    assert(node->func == NULL);
>      node->func = func;
>      enqueue(node);
>      qatomic_inc(&rcu_call_count);

thanks
-- PMM