Hi Eric, On Wed, 2017-03-29 at 14:41 -0700, Eric Dumazet wrote: > On Wed, Mar 29, 2017 at 2:30 PM, David Miller <davem at davemloft.net> wrote: > Signed-off-by: Vlad Zakharov <vzakhar at synopsys.com> > > > > > > Applied. > > > > Eric, if this is really required now, we have 148 broken drivers still. > > Piece of cake :/ > > If we get more reports like that, we might implement a logic to > prevent infinite loops. > > It is not clear to me what exactly happened to this driver, since > testing napi_complete_done() was not mandatory. I am not sure what is happening with other drivers, but in case of ezchip?nps_enet driver after the following commit: 39e6c8208d7b6fb9d2047850fb3327db567b564b if we got into NAPI_STATE_MISSED state the following happened: in nps_enet_poll func we were calling napi_complete_done() (which reset MISSED state but left SCHED state) and after that without any checks were enabling interrupts. Then we obviously were getting into nps_enet_irq_hanlder() if irq was pending (it is very possbile state). If we look inside this function we will see that it disables interrupts only in case napi_sched_prep() returns true. In its turn napi_sched_prep() returns true only in case it changes state from non-SCHED to SCHED. But in our case as SCHED had been already set it set MISSED state and then returned false. So at that point we had already been trapped: after exiting irq hanlder we were getting into nps_enet_irq_hanlder() again and again as we couldn't rescind pending irq signal and disable corresponding irq.? -- Best regards, Vlad Zakharov <vzakhar at synopsys.com>
