From 710c56105dfd10e32a89086cf78cc1c8433f6a7a Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Tue, 18 Mar 2014 17:19:11 +0000 Subject: [PATCH] can: c_can: Remove EOB exit The rx_poll code has the following gem: if (msg_ctrl_save & IF_MCONT_EOB) return num_rx_pkts; The EOB bit is the indicator for the hardware that this is the last configured FIFO object. But this object can contain valid data, if we manage to free up objects before the overrun case hits. Now if the code exits due to the EOB bit set, then this buffer is stale and the interrupt bit and NewDat bit of the buffer are still set. Results in a nice interrupt storm unless we come into an overrun situation where the MSGLST bit gets set. ksoftirqd/0-3 [000] ..s. 79.124101: c_can_poll: rx_poll: val: 00008001 pend 00008001 ksoftirqd/0-3 [000] ..s. 79.124176: c_can_poll: rx_poll: val: 00008000 pend 00008000 ksoftirqd/0-3 [000] ..s. 79.124187: c_can_poll: rx_poll: val: 00008002 pend 00008002 ksoftirqd/0-3 [000] ..s. 79.124256: c_can_poll: rx_poll: val: 00008000 pend 00008000 ksoftirqd/0-3 [000] ..s. 79.124267: c_can_poll: rx_poll: val: 00008000 pend 00008000 The amazing thing is that the check of the MSGLST (aka overrun bit) used to be after the check of the EOB bit. That was "fixed" in commit 5d0f801a2c(can: c_can: Fix RX message handling, handle lost message before EOB). But the author of this "fix" did not even understand that the EOB check is broken as well. Again a simple solution: Remove Signed-off-by: Thomas Gleixner [mkl: adjusted subject and commit message] Signed-off-by: Marc Kleine-Budde --- drivers/net/can/c_can/c_can.c | 3 --- 1 file changed, 3 deletions(-) diff --git a/drivers/net/can/c_can/c_can.c b/drivers/net/can/c_can/c_can.c index ef5f3b8..30a85aa 100644 --- a/drivers/net/can/c_can/c_can.c +++ b/drivers/net/can/c_can/c_can.c @@ -915,9 +915,6 @@ static int c_can_do_rx_poll(struct net_device *dev, int quota) continue; } - if (msg_ctrl_save & IF_MCONT_EOB) - return num_rx_pkts; - if (!(msg_ctrl_save & IF_MCONT_NEWDAT)) continue; -- 2.7.4