linux-kernel - [PATCH] bpf: Call cond_resched() to avoid soft lockup in trie

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Message-Id: <20250616095532.47020-1-matt@readmodwrite.com>
Date: Mon, 16 Jun 2025 10:55:32 +0100
From: Matt Fleming <matt@...dmodwrite.com>
To: Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>
Cc: Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>,
	bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	kernel-team@...udflare.com,
	Matt Fleming <mfleming@...udflare.com>
Subject: [PATCH] bpf: Call cond_resched() to avoid soft lockup in trie_free()

From: Matt Fleming <mfleming@...udflare.com>

Calls to kfree() in trie_free() can be expensive for KASAN-enabled
kernels. This can cause soft lockup warnings when traversing large maps,

  watchdog: BUG: soft lockup - CPU#41 stuck for 76s! [kworker/u518:14:1158211]

Avoid an unbounded loop and periodically check whether we should reschedule.

Signed-off-by: Matt Fleming <mfleming@...udflare.com>
---
 kernel/bpf/lpm_trie.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c
index be66d7e520e0..a35619cd99f6 100644
--- a/kernel/bpf/lpm_trie.c
+++ b/kernel/bpf/lpm_trie.c
@@ -646,6 +646,8 @@ static void trie_free(struct bpf_map *map)
 			RCU_INIT_POINTER(*slot, NULL);
 			break;
 		}
+
+		cond_resched();
 	}
 
 out:
-- 
2.34.1