On Sat, 7 May 2022 13:46:52 +0900
Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
Is this expected to go through the BPF tree?
-- Steve
> Since the rethook_recycle() will involve the call_rcu() for reclaiming
> the rethook_instance, the rethook must be set up at the RCU available
> context (non idle). This rethook_recycle() in the rethook trampoline
> handler is inevitable, thus the RCU available check must be done before
> setting the rethook trampoline.
>
> This adds a rcu_is_watching() check in the rethook_try_get() so that
> it will return NULL if it is called when !rcu_is_watching().
>
> Fixes: 54ecbe6f1ed5 ("rethook: Add a generic return hook")
> Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> ---
> kernel/trace/rethook.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/kernel/trace/rethook.c b/kernel/trace/rethook.c
> index b56833700d23..c69d82273ce7 100644
> --- a/kernel/trace/rethook.c
> +++ b/kernel/trace/rethook.c
> @@ -154,6 +154,15 @@ struct rethook_node *rethook_try_get(struct rethook *rh)
> if (unlikely(!handler))
> return NULL;
>
> + /*
> + * This expects the caller will set up a rethook on a function entry.
> + * When the function returns, the rethook will eventually be reclaimed
> + * or released in the rethook_recycle() with call_rcu().
> + * This means the caller must be run in the RCU-availabe context.
> + */
> + if (unlikely(!rcu_is_watching()))
> + return NULL;
> +
> fn = freelist_try_get(&rh->pool);
> if (!fn)
> return NULL;
