linux-kernel - [PATCH 15/48] bpf: Choose RCU Tasks based on TASKS

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Message-Id: <20240507093530.3043-16-urezki@gmail.com>
Date: Tue,  7 May 2024 11:34:57 +0200
From: "Uladzislau Rezki (Sony)" <urezki@...il.com>
To: "Paul E . McKenney" <paulmck@...nel.org>
Cc: RCU <rcu@...r.kernel.org>,
	Neeraj upadhyay <Neeraj.Upadhyay@....com>,
	Boqun Feng <boqun.feng@...il.com>,
	Hillf Danton <hdanton@...a.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>,
	Frederic Weisbecker <frederic@...nel.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	John Fastabend <john.fastabend@...il.com>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...gle.com>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Ankur Arora <ankur.a.arora@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	bpf@...r.kernel.org
Subject: [PATCH 15/48] bpf: Choose RCU Tasks based on TASKS_RCU rather than PREEMPTION

From: "Paul E. McKenney" <paulmck@...nel.org>

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@...nel.org>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Daniel Borkmann <daniel@...earbox.net>
Cc: John Fastabend <john.fastabend@...il.com>
Cc: Andrii Nakryiko <andrii@...nel.org>
Cc: Martin KaFai Lau <martin.lau@...ux.dev>
Cc: Song Liu <song@...nel.org>
Cc: Yonghong Song <yonghong.song@...ux.dev>
Cc: KP Singh <kpsingh@...nel.org>
Cc: Stanislav Fomichev <sdf@...gle.com>
Cc: Hao Luo <haoluo@...gle.com>
Cc: Jiri Olsa <jolsa@...nel.org>
Cc: Ankur Arora <ankur.a.arora@...cle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: <bpf@...r.kernel.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
---
 kernel/bpf/trampoline.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index db7599c59c78..88673a4267eb 100644
--- 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);
-- 
2.39.2