From: Sebastian Andrzej Siewior Date: Fri, 1 Oct 2021 14:58:41 +0000 (+0200) Subject: net/core: disable NET_RX_BUSY_POLL on PREEMPT_RT X-Git-Tag: v6.6-pxa1908~5313^2~304 X-Git-Url: https://git.dujemihanovic.xyz/?a=commitdiff_plain;h=20ab39d13e2e9f916cf570fc834f2cadd6e5dc4a;p=linux.git 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 Link: https://lore.kernel.org/r/20211001145841.2308454-1-bigeasy@linutronix.de Signed-off-by: Jakub Kicinski --- diff --git a/net/Kconfig b/net/Kconfig index fb13460c6dab..074472dfa94a 100644 --- a/net/Kconfig +++ b/net/Kconfig @@ -294,7 +294,7 @@ config CGROUP_NET_CLASSID config NET_RX_BUSY_POLL bool - default y + default y if !PREEMPT_RT config BQL bool