On Wed, 7 Dec 2016 07:53:26 -0500 Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > On Wed, 7 Dec 2016 10:10:40 +0100 > Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> wrote: > > > On 2016-12-06 17:50:30 [-0500], Steven Rostedt wrote: > > > 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(). > > > > It would work RT wise. But don't have the same problem if you boot the > > kernel with threadirqs ? > > > > I thought the same at first, but looking into the code for forced > threaded interrupts, I saw this: > > local_bh_disable(); > ret = action->thread_fn(action->irq, action->dev_id); > irq_finalize_oneshot(desc, action); > local_bh_enable(); > > Where without CONFIG_PREEMPT_RT_FULL, local_bh_disable() also disables > preemption. Then all the handlers still can not be preempted by another > handler. So it appears to be safe as well. > Actually, I was hoping that the change log explained this. Should I reword it better? "poll_list, which is protected by disabling interrupts (disabling preemption is enough when all interrupts are threaded and local_bh_disable() can't preempt)." -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
