From b3136c7f09d005fe8e04720b5688e2962839559f Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Date: Fri, 1 Oct 2021 16:58:41 +0200 Subject: [PATCH 024/158] net/core: disable NET_RX_BUSY_POLL on PREEMPT_RT napi_busy_loop() disables preemption and performs a NAPI poll. We can't acquire sleeping locks with disabled preemption which would be required while __napi_poll() invokes the callback of the driver. A threaded interrupt performing the NAPI-poll can be preempted on PREEMPT_RT. A RT thread on another CPU may observe NAPIF_STATE_SCHED bit set and busy-spin until it is cleared or its spin time runs out. Given it is the task with the highest priority it will never observe the NEED_RESCHED bit set. In this case the time is better spent by simply sleeping. The NET_RX_BUSY_POLL is disabled by default (the system wide sysctls for poll/read are set to zero). Disabling NET_RX_BUSY_POLL on PREEMPT_RT to avoid wrong locking context in case it is used. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Link: https://lore.kernel.org/r/20211001145841.2308454-1-bigeasy@linutronix.de Signed-off-by: Jakub Kicinski <kuba@kernel.org> --- net/Kconfig | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) Index: linux-5.15.19-rt29/net/Kconfig =================================================================== @ linux-5.15.19-rt29/net/Kconfig:297 @ config CGROUP_NET_CLASSID config NET_RX_BUSY_POLL bool - default y + default y if !PREEMPT_RT config BQL bool