linux-kernel - [PATCH] net: remove local_bh

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Message-Id: <20250829030456.489405-1-lange_tang@163.com>
Date: Fri, 29 Aug 2025 11:04:56 +0800
From: Longjun Tang <lange_tang@....com>
To: davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com
Cc: netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	tanglongjun@...inos.cn,
	lange_tang@....com
Subject: [PATCH] net: remove local_bh_enable during busy poll

From: Longjun Tang <tanglongjun@...inos.cn>

When CONFIG_NET_RX_BUSY_POLL==Y and net.core.busy_read > 0,
the __napi_busy_loop function calls napi_poll to perform busy polling,
such as in the case of virtio_net's virnet_poll. If interrupts are enabled
during the busy polling process, it is possible that data has already been
received and that last_used_idx is updated before the interrupt is handled.
This can lead to the vring_interrupt returning IRQ_NONE in response to the
interrupt because used_idx == last_used_idx, which is considered a spurious
interrupt.Once certain conditions are met, this interrupt can be disabled.

The local_bh_enable during the busy polling process allows softirq to be
executed and interrupt notification to be enabled. Removing local_bh_enable
will significantly reduce the number of unhandled interrupts.

Signed-off-by: Longjun Tang <tanglongjun@...inos.cn>
---
 net/core/dev.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 5a3c0f40a93f..f5737c551666 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6763,12 +6763,12 @@ static void __napi_busy_loop(unsigned int napi_id,
 					LINUX_MIB_BUSYPOLLRXPACKETS, work);
 		skb_defer_free_flush(this_cpu_ptr(&softnet_data));
 		bpf_net_ctx_clear(bpf_net_ctx);
-		local_bh_enable();

 		if (!loop_end || loop_end(loop_end_arg, start_time))
 			break;

 		if (unlikely(need_resched())) {
+			local_bh_enable();
 			if (flags & NAPI_F_END_ON_RESCHED)
 				break;
 			if (napi_poll)
@@ -6784,6 +6784,7 @@ static void __napi_busy_loop(unsigned int napi_id,
 		}
 		cpu_relax();
 	}
+	local_bh_enable();
 	if (napi_poll)
 		busy_poll_stop(napi, have_poll_lock, flags, budget);
 	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
-- 
2.48.1