[RFC] ath9k: Don't let rx tasklet run forever.

[greearb@candelatech.com]

From: Ben Greear <greearb@candelatech.com>

I saw this splat below on a 3.9.11+ kernel system configured to receive
a UDP flood using wpa2 encryption and software-crypt.  This patch attempts
to fix this by returning after processing a max of 1000 packets.

BUG: soft lockup - CPU#0 stuck for 22s! [btserver:32646]
Modules linked in: nfsv4 auth_rpcgss nfs fscache nf_nat_ipv4 nf_nat 8021q garp stp mrp llc macvlan wanlink(O) pktgen lockd sunrpc f71882fg snd_hda_codec_hdmi
snd_hda_codec_realtek snd_hda_intel snd_hda_codec snd_hwdep cdc_acm joydev snd_seq snd_seq_device snd_pcm coretemp ath9k hwmon ath9k_common mperf ath9k_hw
intel_powerclamp ath kvm_intel mac80211 kvm cfg80211 iTCO_wdt microcode iTCO_vendor_support snd_page_alloc e1000e i2c_i801 snd_timer mos7840 pcspkr serio_raw
snd soundcore ptp pps_core lpc_ich uinput ipv6 i915 video i2c_algo_bit drm_kms_helper drm i2c_core [last unloaded: iptable_nat]
CPU 0
Pid: 32646, comm: btserver Tainted: G         C O 3.9.11+ #126 To be filled by O.E.M. To be filled by O.E.M./HURONRIVER
RIP: 0010:[<ffffffff81017e1d>]  [<ffffffff81017e1d>] __kernel_fpu_begin+0x48/0x8b
RSP: 0000:ffff88021fa03918  EFLAGS: 00000286
RAX: 00000000ffffffff RBX: ffffffff81549567 RCX: ffff88020bc48000
RDX: 00000000ffffffff RSI: ffff88021fa03a28 RDI: ffff88020f8d5a00
RBP: ffff88021fa03918 R08: ffff8801b54a1978 R09: 0000000000000010
R10: ffff88020c5cb490 R11: 0000000000000200 R12: ffff88021fa03888
R13: ffffffff815d235d R14: ffff88021fa03918 R15: ffff88020c5cb400
FS:  00007f02f9605740(0000) GS:ffff88021fa00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000023b4c60 CR3: 000000020b754000 CR4: 00000000000407f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process btserver (pid: 32646, threadinfo ffff880210666000, task ffff88020bc48000)
Stack:
  ffff88021fa03928 ffffffff8108b1f2 ffff88021fa03958 ffffffff8108c05d
  ffff88021fa03a28 ffff88021fa03a28 ffff88020c5c9c00 ffff88021fa03a08
  ffff88021fa039d8 ffffffffa05be460 ffff880200000010 ffff8801b54a1978
Call Trace:
  <IRQ>
  [<ffffffff8108b1f2>] kernel_fpu_begin+0x42/0x44
  [<ffffffff8108c05d>] aes_encrypt+0x46/0x62
  [<ffffffffa05be460>] ieee80211_aes_ccm_decrypt+0xcf/0x108 [mac80211]
  [<ffffffffa05b1e0f>] ieee80211_crypto_ccmp_decrypt+0x1c7/0x247 [mac80211]
  [<ffffffffa05c530d>] ieee80211_rx_handlers+0x305/0x18c9 [mac80211]
  [<ffffffff815d235d>] ? apic_timer_interrupt+0x6d/0x80
  [<ffffffffa05c71cf>] ieee80211_prepare_and_rx_handle+0x8fe/0x96a [mac80211]
  [<ffffffffa05c79c4>] ieee80211_rx+0x6e9/0x759 [mac80211]
  [<ffffffffa08f5f99>] ath_rx_tasklet+0xff8/0x10d1 [ath9k]
  [<ffffffffa08f43a1>] ath9k_tasklet+0xf9/0x150 [ath9k]
  [<ffffffff8109d5af>] tasklet_action+0x7d/0xcc
  [<ffffffff8109da08>] __do_softirq+0x114/0x254
  [<ffffffff815caf51>] ? _raw_spin_unlock_irqrestore+0x31/0x3c
  [<ffffffff815caf15>] ? _raw_spin_unlock+0x24/0x2f
  [<ffffffff8109dbda>] irq_exit+0x4b/0xa8
  [<ffffffff815d33dd>] do_IRQ+0x9d/0xb4
  [<ffffffff815cb4ad>] common_interrupt+0x6d/0x6d
  <EOI>
Code: 4c 05 00 00 00 00 00 00 65 48 c7 04 25 b0 c6 00 00 00 00 00 00 b0 01 84 c0 48 8b b9 50 05 00 00 74 1b 83 c8 ff 89 c2 48 0f ae 37 <48> 8b 81 50 05 00 00 f6
80 00 02 00 00 01 75 06 eb 2f 48 0f ae

Signed-off-by: Ben Greear <greearb@candelatech.com>
---
 drivers/net/wireless/ath/ath9k/recv.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/drivers/net/wireless/ath/ath9k/recv.c b/drivers/net/wireless/ath/ath9k/recv.c
index a1b0ec2..b3511c8 100644
--- a/drivers/net/wireless/ath/ath9k/recv.c
+++ b/drivers/net/wireless/ath/ath9k/recv.c
@@ -1162,6 +1162,7 @@ int ath_rx_tasklet(struct ath_softc *sc, int flush, bool hp)
 	u64 tsf = 0;
 	u32 tsf_lower = 0;
 	unsigned long flags;
+	int max_per_round = 1000; /* max of 1000 per call if not flushing */
 
 	if (edma)
 		dma_type = DMA_BIDIRECTIONAL;
@@ -1176,6 +1177,11 @@ int ath_rx_tasklet(struct ath_softc *sc, int flush, bool hp)
 	do {
 		bool decrypt_error = false;
 
+		if (!flush) {
+			if (--max_per_round == 0)
+				break;
+		}
+
 		memset(&rs, 0, sizeof(rs));
 		if (edma)
 			bf = ath_edma_get_next_rx_buf(sc, &rs, qtype);
-- 
1.7.3.4