From: Steven Rostedt Date: Tue, 6 Dec 2016 17:50:30 -0500 Subject: [PATCH] net: Have __napi_schedule_irqoff() disable interrupts on RT Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.18/older/patches-4.18.7-rt5.tar.xz A customer hit a crash where the napi sd->poll_list became corrupted. The customer had the bnx2x driver, which does a __napi_schedule_irqoff() in its interrupt handler. Unfortunately, when running with CONFIG_PREEMPT_RT_FULL, this interrupt handler is run as a thread and is preemptable. The call to ____napi_schedule() must be done with interrupts disabled to protect the per cpu softnet_data's "poll_list, which is protected by disabling interrupts (disabling preemption is enough when all interrupts are threaded and local_bh_disable() can't preempt)." As bnx2x isn't the only driver that does this, the safest thing to do is to make __napi_schedule_irqoff() call __napi_schedule() instead when CONFIG_PREEMPT_RT_FULL is enabled, which will call local_irq_save() before calling ____napi_schedule(). Cc: stable-rt@vger.kernel.org Signed-off-by: Steven Rostedt (Red Hat) Signed-off-by: Sebastian Andrzej Siewior --- include/linux/netdevice.h | 12 ++++++++++++ net/core/dev.c | 2 ++ 2 files changed, 14 insertions(+) --- a/include/linux/netdevice.h +++ b/include/linux/netdevice.h @@ -411,7 +411,19 @@ typedef enum rx_handler_result rx_handle typedef rx_handler_result_t rx_handler_func_t(struct sk_buff **pskb); void __napi_schedule(struct napi_struct *n); + +/* + * When PREEMPT_RT_FULL is defined, all device interrupt handlers + * run as threads, and they can also be preempted (without PREEMPT_RT + * interrupt threads can not be preempted). Which means that calling + * __napi_schedule_irqoff() from an interrupt handler can be preempted + * and can corrupt the napi->poll_list. + */ +#ifdef CONFIG_PREEMPT_RT_FULL +#define __napi_schedule_irqoff(n) __napi_schedule(n) +#else void __napi_schedule_irqoff(struct napi_struct *n); +#endif static inline bool napi_disable_pending(struct napi_struct *n) { --- a/net/core/dev.c +++ b/net/core/dev.c @@ -5470,6 +5470,7 @@ bool napi_schedule_prep(struct napi_stru } EXPORT_SYMBOL(napi_schedule_prep); +#ifndef CONFIG_PREEMPT_RT_FULL /** * __napi_schedule_irqoff - schedule for receive * @n: entry to schedule @@ -5481,6 +5482,7 @@ void __napi_schedule_irqoff(struct napi_ ____napi_schedule(this_cpu_ptr(&softnet_data), n); } EXPORT_SYMBOL(__napi_schedule_irqoff); +#endif bool napi_complete_done(struct napi_struct *n, int work_done) {