Messages in this thread | | | Date | Wed, 7 Dec 2016 07:53:26 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH RT] net: Have __napi_schedule_irqoff() disable interrupts on RT |
| |
On Wed, 7 Dec 2016 10:10:40 +0100 Sebastian Andrzej Siewior <bigeasy@linutronix.de> 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.
-- Steve
| |