[PATCH 3.16 078/245] af_packet: set defaule value for tmo

[Ben Hutchings]

3.16.83-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Mao Wenan <maowenan@xxxxxxxxxx>

commit b43d1f9f7067c6759b1051e8ecb84e82cef569fe upstream.

There is softlockup when using TPACKET_V3:
...
NMI watchdog: BUG: soft lockup - CPU#2 stuck for 60010ms!
(__irq_svc) from [<c0558a0c>] (_raw_spin_unlock_irqrestore+0x44/0x54)
(_raw_spin_unlock_irqrestore) from [<c027b7e8>] (mod_timer+0x210/0x25c)
(mod_timer) from [<c0549c30>]
(prb_retire_rx_blk_timer_expired+0x68/0x11c)
(prb_retire_rx_blk_timer_expired) from [<c027a7ac>]
(call_timer_fn+0x90/0x17c)
(call_timer_fn) from [<c027ab6c>] (run_timer_softirq+0x2d4/0x2fc)
(run_timer_softirq) from [<c021eaf4>] (__do_softirq+0x218/0x318)
(__do_softirq) from [<c021eea0>] (irq_exit+0x88/0xac)
(irq_exit) from [<c0240130>] (msa_irq_exit+0x11c/0x1d4)
(msa_irq_exit) from [<c0209cf0>] (handle_IPI+0x650/0x7f4)
(handle_IPI) from [<c02015bc>] (gic_handle_irq+0x108/0x118)
(gic_handle_irq) from [<c0558ee4>] (__irq_usr+0x44/0x5c)
...

If __ethtool_get_link_ksettings() is failed in
prb_calc_retire_blk_tmo(), msec and tmo will be zero, so tov_in_jiffies
is zero and the timer expire for retire_blk_timer is turn to
mod_timer(&pkc->retire_blk_timer, jiffies + 0),
which will trigger cpu usage of softirq is 100%.

Fixes: f6fb8f100b80 ("af-packet: TPACKET_V3 flexible buffer implementation.")
Tested-by: Xiao Jiangfeng <xiaojiangfeng@xxxxxxxxxx>
Signed-off-by: Mao Wenan <maowenan@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/packet/af_packet.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -608,7 +608,8 @@ static int prb_calc_retire_blk_tmo(struc
 			msec = 1;
 			div = speed / 1000;
 		}
-	}
+	} else
+		return DEFAULT_PRB_RETIRE_TOV;
 
 	mbits = (blk_size_in_bytes * 8) / (1024 * 1024);