[PATCH v2] ath9k: do not return early to fix rcu unlocking

From: Tobias Klausmann
Date: Tue Dec 13 2016 - 12:09:58 EST

Starting with commit d94a461d7a7d ("ath9k: use ieee80211_tx_status_noskb
where possible") the driver uses rcu_read_lock() && rcu_read_unlock(), yet on
returning early in ath_tx_edma_tasklet() the unlock is missing leading to stalls
and suspicious RCU usage:

[ INFO: suspicious RCU usage. ]
4.9.0-rc8 #11 Not tainted
kernel/rcu/tree.c:705 Illegal idle entry in RCU read-side critical section.!

other info that might help us debug this:

RCU used illegally from idle CPU!
rcu_scheduler_active = 1, debug_locks = 0
RCU used illegally from extended quiescent state!
1 lock held by swapper/7/0:
, at:
[<ffffffffa06ed110>] ath_tx_edma_tasklet+0x0/0x450 [ath9k]

stack backtrace:
CPU: 7 PID: 0 Comm: swapper/7 Not tainted 4.9.0-rc8 #11
Hardware name: Acer Aspire V3-571G/VA50_HC_CR, BIOS V2.21 12/16/2013
ffff88025efc3f38 ffffffff8132b1e5 ffff88017ede4540 0000000000000001
ffff88025efc3f68 ffffffff810a25f7 ffff88025efcee60 ffff88017edebdd8
ffff88025eeb5400 0000000000000091 ffff88025efc3f88 ffffffff810c3cd4
Call Trace:
[<ffffffff8132b1e5>] dump_stack+0x68/0x93
[<ffffffff810a25f7>] lockdep_rcu_suspicious+0xd7/0x110
[<ffffffff810c3cd4>] rcu_eqs_enter_common.constprop.85+0x154/0x200
[<ffffffff810c5a54>] rcu_irq_exit+0x44/0xa0
[<ffffffff81058631>] irq_exit+0x61/0xd0
[<ffffffff81018d25>] do_IRQ+0x65/0x110
[<ffffffff81672189>] common_interrupt+0x89/0x89
[<ffffffff814ffe11>] ? cpuidle_enter_state+0x151/0x200
[<ffffffff814ffee2>] cpuidle_enter+0x12/0x20
[<ffffffff8109a6ae>] call_cpuidle+0x1e/0x40
[<ffffffff8109a8f6>] cpu_startup_entry+0x146/0x220
[<ffffffff810336f8>] start_secondary+0x148/0x170

Signed-off-by: Tobias Klausmann <tobias.johannes.klausmann@xxxxxxxxxx>
Fixes: d94a461d7a7d ("ath9k: use ieee80211_tx_status_noskb where possible")
Cc: <stable@xxxxxxxxxxxxxxx> # v4.9

v2: break instead of unlock (rename patch) [Felix Fietkau],
fix reference to commit [Kalle Valo]
drivers/net/wireless/ath/ath9k/xmit.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/wireless/ath/ath9k/xmit.c b/drivers/net/wireless/ath/ath9k/xmit.c
index 52bfbb988611..e47286bf378e 100644
--- a/drivers/net/wireless/ath/ath9k/xmit.c
+++ b/drivers/net/wireless/ath/ath9k/xmit.c
@@ -2787,7 +2787,7 @@ void ath_tx_edma_tasklet(struct ath_softc *sc)
fifo_list = &txq->txq_fifo[txq->txq_tailidx];
if (list_empty(fifo_list)) {
ath_txq_unlock(sc, txq);
- return;
+ break;

bf = list_first_entry(fifo_list, struct ath_buf, list);