bpf: Choose RCU Tasks based on TASKS_RCU rather than PREEMPTION

The advent of CONFIG_PREEMPT_AUTO, AKA lazy preemption, will mean that
even kernels built with CONFIG_PREEMPT_NONE or CONFIG_PREEMPT_VOLUNTARY
might see the occasional preemption, and that this preemption just might
happen within a trampoline.

Therefore, update bpf_tramp_image_put() to choose call_rcu_tasks()
based on CONFIG_TASKS_RCU instead of CONFIG_PREEMPTION.

This change might enable further simplifications, but the goal of this
effort is to make the code safe, not necessarily optimal.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Song Liu <song@kernel.org>
Cc: Yonghong Song <yonghong.song@linux.dev>
Cc: KP Singh <kpsingh@kernel.org>
Cc: Stanislav Fomichev <sdf@google.com>
Cc: Hao Luo <haoluo@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Ankur Arora <ankur.a.arora@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: <bpf@vger.kernel.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>

diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index db7599c59c78a66f1b85ef969ba64be084edd181..88673a4267ebdfc118e3048dca761d08565c5568 100644 (file)
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -333,7 +333,7 @@ static void bpf_tramp_image_put(struct bpf_tramp_image *im)
                int err = bpf_arch_text_poke(im->ip_after_call, BPF_MOD_JUMP,
                                             NULL, im->ip_epilogue);
                WARN_ON(err);
-               if (IS_ENABLED(CONFIG_PREEMPTION))
+               if (IS_ENABLED(CONFIG_TASKS_RCU))
                        call_rcu_tasks(&im->rcu, __bpf_tramp_image_put_rcu_tasks);
                else
                        percpu_ref_kill(&im->pcref);