gianfar: Simplify MQ polling to avoid soft lockup

Under certain low traffic conditions, the single core
devices with multiple Rx/Tx queues (MQ mode) may reach
soft lockup due to gfar_poll not returning in proper time.
The following exception was obtained using iperf on a 100Mbit
half-duplex link, for a p1010 single core device:

BUG: soft lockup - CPU#0 stuck for 23s! [iperf:2847]
Modules linked in:
CPU: 0 PID: 2847 Comm: iperf Not tainted 3.12.0-rc3 #16
task: e8bf8000 ti: eeb16000 task.ti: ee646000
NIP: c0255b6c LR: c0367ae8 CTR: c0461c18
REGS: eeb17e70 TRAP: 0901   Not tainted  (3.12.0-rc3)
MSR: 00029000 <CE,EE,ME>  CR: 44228428  XER: 20000000

GPR00: c0367ad4 eeb17f20 e8bf8000 ee01f4b4 00000008 ffffffff ffffffff
00000000
GPR08: 000000c0 00000008 000000ff ffffffc0 000193fe
NIP [c0255b6c] find_next_bit+0xb8/0xc4
LR [c0367ae8] gfar_poll+0xc8/0x1d8
Call Trace:
[eeb17f20] [c0367ad4] gfar_poll+0xb4/0x1d8 (unreliable)
[eeb17f70] [c0422100] net_rx_action+0xa4/0x158
[eeb17fa0] [c003ec6c] __do_softirq+0xcc/0x17c
[eeb17ff0] [c000c28c] call_do_softirq+0x24/0x3c
[ee647cc0] [c0004660] do_softirq+0x6c/0x94
[ee647ce0] [c003eb9c] local_bh_enable+0x9c/0xa0
[ee647cf0] [c0454fe8] tcp_prequeue_process+0xa4/0xdc
[ee647d10] [c0457e44] tcp_recvmsg+0x498/0x96c
[ee647d80] [c047b630] inet_recvmsg+0x40/0x64
[ee647da0] [c040ca8c] sock_recvmsg+0x90/0xc0
[ee647e30] [c040edb8] SyS_recvfrom+0x98/0xfc

To prevent this, the outer while() loop has been removed
allowing gfar_poll() to return faster even if there's
still budget left.  Also, there's no need to recompute
the budget per Rx queue anymore.

Signed-off-by: Claudiu Manoil <claudiu.manoil@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/freescale/gianfar.c b/drivers/net/ethernet/freescale/gianfar.c
index c4eaadeb572fa3dcd97396afffd961f936d0189d..186dc4a489a46f2e0fcd472f73c2f187515bb848 100644 (file)
--- a/drivers/net/ethernet/freescale/gianfar.c
+++ b/drivers/net/ethernet/freescale/gianfar.c
@@ -2900,7 +2900,7 @@ static int gfar_poll(struct napi_struct *napi, int budget)
        struct gfar_priv_rx_q *rx_queue = NULL;
        int work_done = 0, work_done_per_q = 0;
        int i, budget_per_q = 0;
-       int has_tx_work;
+       int has_tx_work = 0;
        unsigned long rstat_rxf;
        int num_act_queues;
 
@@ -2915,62 +2915,51 @@ static int gfar_poll(struct napi_struct *napi, int budget)
        if (num_act_queues)
                budget_per_q = budget/num_act_queues;
 
-       while (1) {
-               has_tx_work = 0;
-               for_each_set_bit(i, &gfargrp->tx_bit_map, priv->num_tx_queues) {
-                       tx_queue = priv->tx_queue[i];
-                       /* run Tx cleanup to completion */
-                       if (tx_queue->tx_skbuff[tx_queue->skb_dirtytx]) {
-                               gfar_clean_tx_ring(tx_queue);
-                               has_tx_work = 1;
-                       }
+       for_each_set_bit(i, &gfargrp->tx_bit_map, priv->num_tx_queues) {
+               tx_queue = priv->tx_queue[i];
+               /* run Tx cleanup to completion */
+               if (tx_queue->tx_skbuff[tx_queue->skb_dirtytx]) {
+                       gfar_clean_tx_ring(tx_queue);
+                       has_tx_work = 1;
                }
+       }
 
-               for_each_set_bit(i, &gfargrp->rx_bit_map, priv->num_rx_queues) {
-                       /* skip queue if not active */
-                       if (!(rstat_rxf & (RSTAT_CLEAR_RXF0 >> i)))
-                               continue;
-
-                       rx_queue = priv->rx_queue[i];
-                       work_done_per_q =
-                               gfar_clean_rx_ring(rx_queue, budget_per_q);
-                       work_done += work_done_per_q;
-
-                       /* finished processing this queue */
-                       if (work_done_per_q < budget_per_q) {
-                               /* clear active queue hw indication */
-                               gfar_write(&regs->rstat,
-                                          RSTAT_CLEAR_RXF0 >> i);
-                               rstat_rxf &= ~(RSTAT_CLEAR_RXF0 >> i);
-                               num_act_queues--;
-
-                               if (!num_act_queues)
-                                       break;
-                               /* recompute budget per Rx queue */
-                               budget_per_q =
-                                       (budget - work_done) / num_act_queues;
-                       }
-               }
+       for_each_set_bit(i, &gfargrp->rx_bit_map, priv->num_rx_queues) {
+               /* skip queue if not active */
+               if (!(rstat_rxf & (RSTAT_CLEAR_RXF0 >> i)))
+                       continue;
 
-               if (work_done >= budget)
-                       break;
+               rx_queue = priv->rx_queue[i];
+               work_done_per_q =
+                       gfar_clean_rx_ring(rx_queue, budget_per_q);
+               work_done += work_done_per_q;
+
+               /* finished processing this queue */
+               if (work_done_per_q < budget_per_q) {
+                       /* clear active queue hw indication */
+                       gfar_write(&regs->rstat,
+                                  RSTAT_CLEAR_RXF0 >> i);
+                       num_act_queues--;
+
+                       if (!num_act_queues)
+                               break;
+               }
+       }
 
-               if (!num_act_queues && !has_tx_work) {
+       if (!num_act_queues && !has_tx_work) {
 
-                       napi_complete(napi);
+               napi_complete(napi);
 
-                       /* Clear the halt bit in RSTAT */
-                       gfar_write(&regs->rstat, gfargrp->rstat);
+               /* Clear the halt bit in RSTAT */
+               gfar_write(&regs->rstat, gfargrp->rstat);
 
-                       gfar_write(&regs->imask, IMASK_DEFAULT);
+               gfar_write(&regs->imask, IMASK_DEFAULT);
 
-                       /* If we are coalescing interrupts, update the timer
-                        * Otherwise, clear it
-                        */
-                       gfar_configure_coalescing(priv, gfargrp->rx_bit_map,
-                                                 gfargrp->tx_bit_map);
-                       break;
-               }
+               /* If we are coalescing interrupts, update the timer
+                * Otherwise, clear it
+                */
+               gfar_configure_coalescing(priv, gfargrp->rx_bit_map,
+                                         gfargrp->tx_bit_map);
        }
 
        return work_done;