2012-05-04 13:43:18

by Larry Finger

Subject: [PATCH] mac80211: Fix 'suspicious RCU usage' warning

From: Johannes Berg <[email protected]>

When running kernel 3.4-rc2 from wireless testing, the following is logged:

[ INFO: suspicious RCU usage. ]
3.4.0-rc2-wl+ #222 Not tainted
-------------------------------
net/mac80211/sta_info.h:449 suspicious rcu_dereference_protected() usage!

other info that might help us debug this:


rcu_scheduler_active = 1, debug_locks = 0
1 lock held by swapper/1/0:
#0: (&tid_tx->session_timer){+.-...}, at: [<ffffffff8104850a>] run_timer_softirq+0xfa/0x6e0

stack backtrace:
Pid: 0, comm: swapper/1 Not tainted 3.4.0-rc2-wl+ #222
Call Trace:
<IRQ> [<ffffffff81092fdd>] lockdep_rcu_suspicious+0xfd/0x130
[<ffffffffa05db673>] sta_tx_agg_session_timer_expired+0xe3/0x100 [mac80211]
[<ffffffff81048595>] run_timer_softirq+0x185/0x6e0
[<ffffffff8104850a>] ? run_timer_softirq+0xfa/0x6e0
[<ffffffffa05db590>] ? ieee80211_stop_tx_ba_session+0x240/0x240 [mac80211]
[<ffffffff81040156>] __do_softirq+0xc6/0x3f0
[<ffffffff8139c934>] ? _raw_spin_lock+0x44/0x50
[<ffffffff8139d0f6>] ? _raw_spin_unlock+0x26/0x40
[<ffffffff8139f24c>] call_softirq+0x1c/0x30
[<ffffffff81004785>] do_softirq+0x85/0xc0
[<ffffffff810407b6>] irq_exit+0xa6/0xe0
[<ffffffff8100424e>] do_IRQ+0x5e/0xd0
[<ffffffff8139d56c>] common_interrupt+0x6c/0x6c
<EOI> [<ffffffff8100c042>] ? default_idle+0x62/0x4f0
[<ffffffff8100c040>] ? default_idle+0x60/0x4f0
[<ffffffff8100c524>] amd_e400_idle+0x54/0x100
[<ffffffff8100ce96>] cpu_idle+0x96/0xe0
[<ffffffff8138fbc6>] start_secondary+0x1b7/0x1bb

Reported-and-tested-by:: Larry Finger <[email protected]>
Signed-off-by: Johannes Berg <[email protected]>
Signed-off-by: Larry Finger <[email protected]>
---

John,

This patch affects 3.4.

Larry
---

Index: wireless-testing-new/net/mac80211/agg-tx.c
===================================================================
--- wireless-testing-new.orig/net/mac80211/agg-tx.c
+++ wireless-testing-new/net/mac80211/agg-tx.c
@@ -421,16 +421,22 @@ static void sta_tx_agg_session_timer_exp
struct tid_ampdu_tx *tid_tx;
unsigned long timeout;

- tid_tx = rcu_dereference_protected_tid_tx(sta, *ptid);
- if (!tid_tx)
+ rcu_read_lock();
+ tid_tx = rcu_dereference(sta->ampdu_mlme.tid_tx[*ptid]);
+ if (!tid_tx) {
+ rcu_read_unlock();
return;
+ }

timeout = tid_tx->last_tx + TU_TO_JIFFIES(tid_tx->timeout);
if (time_is_after_jiffies(timeout)) {
mod_timer(&tid_tx->session_timer, timeout);
+ rcu_read_unlock();
return;
}

+ rcu_read_unlock();
+
#ifdef CONFIG_MAC80211_HT_DEBUG
printk(KERN_DEBUG "tx session timer expired on tid %d\n", (u16)*ptid);
#endif

2012-05-05 15:39:25

by Larry Finger

Subject: Re: [PATCH] mac80211: Fix 'suspicious RCU usage' warning

On 05/05/2012 10:19 AM, Johannes Berg wrote:
> On Fri, 2012-05-04 at 08:43 -0500, Larry Finger wrote:
>> From: Johannes Berg<[email protected]>
>>
>> When running kernel 3.4-rc2 from wireless testing, the following is logged:
>
>> Reported-and-tested-by:: Larry Finger<[email protected]>
>> Signed-off-by: Johannes Berg<[email protected]>
>
> Wait wait, I never signed this off yet. You really can't pretend I did.

Sorry. I thought you did.

Larry

2012-05-05 15:19:14

by Johannes Berg

Subject: Re: [PATCH] mac80211: Fix 'suspicious RCU usage' warning

On Fri, 2012-05-04 at 08:43 -0500, Larry Finger wrote:
> From: Johannes Berg <[email protected]>
>
> When running kernel 3.4-rc2 from wireless testing, the following is logged:

> Reported-and-tested-by:: Larry Finger <[email protected]>
> Signed-off-by: Johannes Berg <[email protected]>

Wait wait, I never signed this off yet. You really can't pretend I did.

johannes