Re: [Make-wifi-fast] [PATCH RFC v4 3/4] mac80211: Add airtime accounting and scheduling to TXQs

[Rajkumar Manoharan <rmanohar@codeaurora.org>]

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On 2018-10-01 23:58, Rajkumar Manoharan wrote:
>> Great! I'll fold in the rest, test it with ath9k and submit as a 
>> proper patch :)
>> 
> Toke,
> 
> I noticed a race condition b/w sta cleanup and kick_airtime tasklet. 
> How do you
> plan to exit kick_airtime gracefully during sta_cleanup?
> 
If kick_airtime tasklet is only used for adjusting deficit for all 
throttled txq,
then below rcu lock issue is not observed. I am testing with 50 clients 
and the
crash happens only during sta cleanup. Releasing active_txq_lock from 
tasklet is
yielding handle to txq_purge(). I am thinking of get rid of tasklet and 
handle
adjustment directly in API.


diff --git a/net/mac80211/util.c b/net/mac80211/util.c
index 0bb590928dd0..277dbf8e0a4b 100644
--- a/net/mac80211/util.c
+++ b/net/mac80211/util.c
@@ -261,14 +261,7 @@ static void __ieee80211_kick_airtime(struct 
ieee80211_local *local, int ac)

                 if (sta->airtime[ac].deficit >= 0) {
                         seen_eligible = true;
-
-                       if 
(!test_and_clear_bit(IEEE80211_TXQ_AIRTIME_THROTTLE,
-                                               &txqi->flags))
-                               continue;
-
-                       spin_unlock_bh(&local->active_txq_lock[ac]);
-                       drv_wake_tx_queue(local, txqi);
-                       spin_lock_bh(&local->active_txq_lock[ac]);
+                       clear_bit(IEEE80211_TXQ_AIRTIME_THROTTLE, 
&txqi->flags);

-Rajkumar

[-- Attachment #2: rcu_race.txt --]
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root@OpenWrt:/# [  363.094702] INFO: rcu_preempt self-detected stall on CPU { 0}
  (t=2101 jiffies g=2679 c=2678 q=134)
[  363.102709] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.14.77 #9
[  363.104717] INFO: rcu_preempt detected stalls on CPUs/tasks: { 0} (detected b
y 1, t=2102 jiffies, g=2679, c=2678, q=134)
[  363.104723] Task dump for CPU 0:
[  363.104734] swapper/0       R running      0     0      0 0x00001002
[  363.104763] [<c020ec20>] (__schedule) from [<c0218304>] (arch_cpu_idle+0x38/0
x5c)
[  363.104852] [<c0218304>] (arch_cpu_idle) from [<ffffffff>] (0xffffffff)
[  363.143167] [<c021d9ac>] (unwind_backtrace) from [<c021aa40>] (show_stack+0x1
0/0x14)
[  363.150892] [<c021aa40>] (show_stack) from [<c03c59d4>] (dump_stack+0x80/0xa0
)
[  363.158099] [<c03c59d4>] (dump_stack) from [<c026e1dc>] (rcu_check_callbacks+
0x230/0x6a8)
[  363.166258] [<c026e1dc>] (rcu_check_callbacks) from [<c0238814>] (update_proc
ess_times+0x38/0x58)
[  363.175110] [<c0238814>] (update_process_times) from [<c0276780>] (tick_sched
_timer+0x44/0x74)
[  363.183702] [<c0276780>] (tick_sched_timer) from [<c024a828>] (__run_hrtimer+
0x50/0xc8)
[  363.191686] [<c024a828>] (__run_hrtimer) from [<c024aff8>] (hrtimer_interrupt
+0x130/0x27c)
[  363.199936] [<c024aff8>] (hrtimer_interrupt) from [<c05175ac>] (msm_timer_int
errupt+0x38/0x44)
[  363.208528] [<c05175ac>] (msm_timer_interrupt) from [<c0268a6c>] (handle_perc
pu_devid_irq+0x68/0x84)
[  363.217645] [<c0268a6c>] (handle_percpu_devid_irq) from [<c02653e0>] (generic
_handle_irq+0x20/0x30)
[  363.226671] [<c02653e0>] (generic_handle_irq) from [<c021803c>] (handle_IRQ+0
x68/0x90)
[  363.234567] [<c021803c>] (handle_IRQ) from [<c02084e0>] (gic_handle_irq+0x3c/
0x60)
[  363.242120] [<c02084e0>] (gic_handle_irq) from [<c02095c0>] (__irq_svc+0x40/0
x70)
[  363.249581] Exception stack(0xc085de68 to 0xc085deb0)
[  363.254616] de60:                   00000004 db7e50a0 0000009d 00000000 d8bb8
d18 d8bb8d00
[  363.262777] de80: d8bb8c20 00000002 00000030 00000018 db7e5000 00000006 00000
000 c085deb0
[  363.270935] dea0: bfb68c98 c020cae8 60000113 ffffffff
[  363.275977] [<c02095c0>] (__irq_svc) from [<c020cae8>] (_test_and_clear_bit+0
x0/0x48)
[  363.283850] [<c020cae8>] (_test_and_clear_bit) from [<bfb68c98>] (ieee80211_k
ick_airtime+0x88/0x188 [mac80211])
[  363.293963] [<bfb68c98>] (ieee80211_kick_airtime [mac80211]) from [<c02331ec>
] (tasklet_action+0x8c/0xec)
[  363.303406] [<c02331ec>] (tasklet_action) from [<c02327e4>] (__do_softirq+0x1
04/0x294)