[15/48] bpf: Choose RCU Tasks based on TASKS_RCU rather than PREEMPTION

Commit Message

Uladzislau Rezki May 7, 2024, 9:34 a.m. UTC

From: "Paul E. McKenney" <[e-mail]>

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 <[e-mail]>
Cc: Alexei Starovoitov <[e-mail]>
Cc: Daniel Borkmann <[e-mail]>
Cc: John Fastabend <[e-mail]>
Cc: Andrii Nakryiko <[e-mail]>
Cc: Martin KaFai Lau <[e-mail]>
Cc: Song Liu <[e-mail]>
Cc: Yonghong Song <[e-mail]>
Cc: KP Singh <[e-mail]>
Cc: Stanislav Fomichev <[e-mail]>
Cc: Hao Luo <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Ankur Arora <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Uladzislau Rezki (Sony) <[e-mail]>
---
 kernel/bpf/trampoline.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Patch

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);