On Wed, 14 Apr 2021 03:08:45 -0500 Lijun Pan wrote: > There are chances that napi_disable can be called twice by NIC driver. > This could generate deadlock. For example, > the first napi_disable will spin until NAPI_STATE_SCHED is cleared > by napi_complete_done, then set it again. > When napi_disable is called the second time, it will loop infinitely > because no dev->poll will be running to clear NAPI_STATE_SCHED. > > Though it is driver writer's responsibility to make sure it being > called only once, making napi_disable more robust does not hurt, not > to say it can prevent a buggy driver from crashing a system. > So, we check the napi state bit to make sure that if napi is already > disabled, we exit the call early enough to avoid spinning infinitely.
You've already been told by Eric & Dave to fix the driver instead. Your check is _not_ correct - SCHED && NPSVC && !MISSED && !BUSY_POLL can well arise without disabling the NAPI. But regardless, a driver bug should be relatively easy to identify with task getting stuck in napi_disable(). We don't provide "protection" for taking spin locks or ref counts twice either. Unless you can show a strong use case please stop posting new versions of this patch.
