Re: [PATCH] ath9k_htc: Add a missing spin_lock_init()

From: Rajat Asthana
Date: Wed Jul 28 2021 - 15:02:49 EST

On 28/07/21 12:41 pm, Kalle Valo wrote:
Rajat Asthana <rajatasthana4@xxxxxxxxx> writes:

Syzkaller reported a lockdep warning on non-initialized spinlock:

INFO: trying to register non-static key.
The code is fine but needs lockdep annotation, or maybe
you didn't initialize this object before use?
turning off the locking correctness validator.
CPU: 0 PID: 10 Comm: ksoftirqd/0 Not tainted 5.13.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:79 [inline]
dump_stack+0x143/0x1db lib/dump_stack.c:120
assign_lock_key kernel/locking/lockdep.c:937 [inline]
register_lock_class+0x1077/0x1180 kernel/locking/lockdep.c:1249
__lock_acquire+0x102/0x5230 kernel/locking/lockdep.c:4781
lock_acquire kernel/locking/lockdep.c:5512 [inline]
lock_acquire+0x19d/0x700 kernel/locking/lockdep.c:5477
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline]
_raw_spin_lock_bh+0x2f/0x40 kernel/locking/spinlock.c:175
spin_lock_bh include/linux/spinlock.h:359 [inline]
ath9k_wmi_event_tasklet+0x231/0x3f0 drivers/net/wireless/ath/ath9k/wmi.c:172
tasklet_action_common.constprop.0+0x201/0x2e0 kernel/softirq.c:784
__do_softirq+0x1b0/0x944 kernel/softirq.c:559
run_ksoftirqd kernel/softirq.c:921 [inline]
run_ksoftirqd+0x21/0x50 kernel/softirq.c:913
smpboot_thread_fn+0x3ec/0x870 kernel/smpboot.c:165
kthread+0x38c/0x460 kernel/kthread.c:313
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

We missed a spin_lock_init() in ath9k_wmi_event_tasklet() when the wmi
event is WMI_TXSTATUS_EVENTID. Placing this init here instead of
ath9k_init_wmi() is fine mainly because we need this spinlock when the
event is WMI_TXSTATUS_EVENTID and hence it should be initialized when it
is needed.

Signed-off-by: Rajat Asthana <rajatasthana4@xxxxxxxxx>
drivers/net/wireless/ath/ath9k/wmi.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/drivers/net/wireless/ath/ath9k/wmi.c b/drivers/net/wireless/ath/ath9k/wmi.c
index fe29ad4b9023..446b7ca459df 100644
--- a/drivers/net/wireless/ath/ath9k/wmi.c
+++ b/drivers/net/wireless/ath/ath9k/wmi.c
@@ -169,6 +169,7 @@ void ath9k_wmi_event_tasklet(struct tasklet_struct *t)
+ spin_lock_init(&priv->tx.tx_lock);
if (priv->tx.flags & ATH9K_HTC_OP_TX_DRAIN) {

This is not making sense to me. You need to elaborate in the commit log
a lot more why this is "fine". For example, what happens when there are
multiple WMI_TXSTATUS_EVENTID events?

Thanks for the review!
Now that you mentioned the case when there are multiple WMI_TXSTATUS_EVENTID events, this doesn't make sense, as that will cause a race condition. This instead should be done in ath9k_init_wmi(). I will make this change in the v2 patch.

Did you test this on a real device?

No, I didn't test this on a real device. Syzkaller has a reproducer for this and I just relied on the fact that the reproducer did not reproduce the warning with this patch.