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[PATCH] ath9k: unlock rcu read when returning early

Started byTobias Klausmann <tobias.johannes.klausmann@mni.thm.de>
First post2016-12-12 20:00 +0100
Last post2016-12-21 15:30 +0100
Articles 8 — 4 participants

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  [PATCH] ath9k: unlock rcu read when returning early Tobias Klausmann <tobias.johannes.klausmann@mni.thm.de> - 2016-12-12 20:00 +0100
    Re: [PATCH] ath9k: unlock rcu read when returning early Kalle Valo <kvalo@codeaurora.org> - 2016-12-13 11:10 +0100
    Re: [PATCH] ath9k: unlock rcu read when returning early Felix Fietkau <nbd@nbd.name> - 2016-12-13 11:50 +0100
      Re: [PATCH] ath9k: unlock rcu read when returning early Tobias Klausmann <tobias.johannes.klausmann@mni.thm.de> - 2016-12-13 14:50 +0100
        Re: [PATCH] ath9k: unlock rcu read when returning early Felix Fietkau <nbd@nbd.name> - 2016-12-13 15:00 +0100
      [PATCH v2] ath9k: do not return early to fix rcu unlocking Tobias Klausmann <tobias.johannes.klausmann@mni.thm.de> - 2016-12-13 18:20 +0100
        Re: [PATCH v2] ath9k: do not return early to fix rcu unlocking Felix Fietkau <nbd@nbd.name> - 2016-12-14 21:50 +0100
        Re: [v2] ath9k: do not return early to fix rcu unlocking Kalle Valo <kvalo@qca.qualcomm.com> - 2016-12-21 15:30 +0100

#1540550 — [PATCH] ath9k: unlock rcu read when returning early

FromTobias Klausmann <tobias.johannes.klausmann@mni.thm.de>
Date2016-12-12 20:00 +0100
Subject[PATCH] ath9k: unlock rcu read when returning early
Message-ID<sNDZo-7SF-15@gated-at.bofh.it>
Starting with ath9k: use ieee80211_tx_status_noskb where possible
[d94a461d7a7df68991fb9663531173f60ef89c68] 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:
 #0:
  (
 rcu_read_lock
 ){......}
 , 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:
  <IRQ>
  [<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
  <EOI>
  [<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@mni.thm.de>
---
 drivers/net/wireless/ath/ath9k/xmit.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/wireless/ath/ath9k/xmit.c b/drivers/net/wireless/ath/ath9k/xmit.c
index 52bfbb988611..857d5ae09a1d 100644
--- a/drivers/net/wireless/ath/ath9k/xmit.c
+++ b/drivers/net/wireless/ath/ath9k/xmit.c
@@ -2787,6 +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);
+			rcu_read_unlock();
 			return;
 		}
 
-- 
2.11.0

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#1540953

FromKalle Valo <kvalo@codeaurora.org>
Date2016-12-13 11:10 +0100
Message-ID<sNSc1-8lZ-13@gated-at.bofh.it>
In reply to#1540550
Tobias Klausmann <tobias.johannes.klausmann@mni.thm.de> writes:

> Starting with ath9k: use ieee80211_tx_status_noskb where possible
> [d94a461d7a7df68991fb9663531173f60ef89c68]

The correct format to reference a commit in the commit log is:

Starting with commit d94a461d7a7d ("ath9k: use ieee80211_tx_status_noskb
where possible") the...

> 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:
>  #0:
>   (
>  rcu_read_lock
>  ){......}
>  , 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:
>   <IRQ>
>   [<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
>   <EOI>
>   [<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@mni.thm.de>

A fixes line and cc stable would be good to have:

Fixes: d94a461d7a7d ("ath9k: use ieee80211_tx_status_noskb where possible")
Cc: <stable@vger.kernel.org> # v4.9

I can add those.

I'm planning to push this to 4.10 but would prefer to see an ack from
Felix (the author of d94a461d7a7d) first. I added him to Cc.

-- 
Kalle Valo

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#1540979

FromFelix Fietkau <nbd@nbd.name>
Date2016-12-13 11:50 +0100
Message-ID<sNSOJ-7j-7@gated-at.bofh.it>
In reply to#1540550
On 2016-12-12 19:50, Tobias Klausmann wrote:
> Starting with ath9k: use ieee80211_tx_status_noskb where possible
> [d94a461d7a7df68991fb9663531173f60ef89c68] 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:
>  #0:
>   (
>  rcu_read_lock
>  ){......}
>  , 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:
>   <IRQ>
>   [<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
>   <EOI>
>   [<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@mni.thm.de>
> ---
>  drivers/net/wireless/ath/ath9k/xmit.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/net/wireless/ath/ath9k/xmit.c b/drivers/net/wireless/ath/ath9k/xmit.c
> index 52bfbb988611..857d5ae09a1d 100644
> --- a/drivers/net/wireless/ath/ath9k/xmit.c
> +++ b/drivers/net/wireless/ath/ath9k/xmit.c
> @@ -2787,6 +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);
> +			rcu_read_unlock();
Technically this is fine as well, but I'd prefer a fix where you replace
the 'return' with 'break', thus avoiding the duplication of
rcu_read_unlock()

Thanks,

- Felix

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#1541076

FromTobias Klausmann <tobias.johannes.klausmann@mni.thm.de>
Date2016-12-13 14:50 +0100
Message-ID<sNVCW-1NI-15@gated-at.bofh.it>
In reply to#1540979

On 13.12.2016 11:41, Felix Fietkau wrote:
> On 2016-12-12 19:50, Tobias Klausmann wrote:
>> Starting with ath9k: use ieee80211_tx_status_noskb where possible
>> [d94a461d7a7df68991fb9663531173f60ef89c68] 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:
>>   #0:
>>    (
>>   rcu_read_lock
>>   ){......}
>>   , 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:
>>    <IRQ>
>>    [<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
>>    <EOI>
>>    [<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@mni.thm.de>
>> ---
>>   drivers/net/wireless/ath/ath9k/xmit.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/net/wireless/ath/ath9k/xmit.c b/drivers/net/wireless/ath/ath9k/xmit.c
>> index 52bfbb988611..857d5ae09a1d 100644
>> --- a/drivers/net/wireless/ath/ath9k/xmit.c
>> +++ b/drivers/net/wireless/ath/ath9k/xmit.c
>> @@ -2787,6 +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);
>> +			rcu_read_unlock();
> Technically this is fine as well, but I'd prefer a fix where you replace
> the 'return' with 'break', thus avoiding the duplication of
> rcu_read_unlock()

Actually if you want to avoid it, maybe skipping over the rest is better 
(as originally intended):

...

ath_txq_unlock(sc, txq);


goto unlock;
}
...

unlock:
rcu_read_unlock();

Thanks,
Tobias
>
> Thanks,
>
> - Felix
>

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#1541089

FromFelix Fietkau <nbd@nbd.name>
Date2016-12-13 15:00 +0100
Message-ID<sNVMC-1R9-31@gated-at.bofh.it>
In reply to#1541076
On 2016-12-13 14:41, Tobias Klausmann wrote:
> On 13.12.2016 11:41, Felix Fietkau wrote:
>> On 2016-12-12 19:50, Tobias Klausmann wrote:
>>> diff --git a/drivers/net/wireless/ath/ath9k/xmit.c b/drivers/net/wireless/ath/ath9k/xmit.c
>>> index 52bfbb988611..857d5ae09a1d 100644
>>> --- a/drivers/net/wireless/ath/ath9k/xmit.c
>>> +++ b/drivers/net/wireless/ath/ath9k/xmit.c
>>> @@ -2787,6 +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);
>>> +			rcu_read_unlock();
>> Technically this is fine as well, but I'd prefer a fix where you replace
>> the 'return' with 'break', thus avoiding the duplication of
>> rcu_read_unlock()
> 
> Actually if you want to avoid it, maybe skipping over the rest is better 
> (as originally intended):
> 
> ...
> 
> ath_txq_unlock(sc, txq);
> 
> 
> goto unlock;
> }
> ...
> 
> unlock:
> rcu_read_unlock();
There are already other places that skip to the rcu_read_unlock() part
by using 'break'. I don't see how adding an unnecessary goto makes
things any better.

- Felix

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#1541270 — [PATCH v2] ath9k: do not return early to fix rcu unlocking

FromTobias Klausmann <tobias.johannes.klausmann@mni.thm.de>
Date2016-12-13 18:20 +0100
Subject[PATCH v2] ath9k: do not return early to fix rcu unlocking
Message-ID<sNYU9-3UP-1@gated-at.bofh.it>
In reply to#1540979
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:
 #0:
  (
 rcu_read_lock
 ){......}
 , 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:
  <IRQ>
  [<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
  <EOI>
  [<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@mni.thm.de>
Fixes: d94a461d7a7d ("ath9k: use ieee80211_tx_status_noskb where possible")
Cc: <stable@vger.kernel.org> # 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);
-- 
2.11.0

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#1542192 — Re: [PATCH v2] ath9k: do not return early to fix rcu unlocking

FromFelix Fietkau <nbd@nbd.name>
Date2016-12-14 21:50 +0100
SubjectRe: [PATCH v2] ath9k: do not return early to fix rcu unlocking
Message-ID<sOoEW-41k-27@gated-at.bofh.it>
In reply to#1541270
On 2016-12-13 18:08, Tobias Klausmann wrote:
> 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:
>  #0:
>   (
>  rcu_read_lock
>  ){......}
>  , 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:
>   <IRQ>
>   [<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
>   <EOI>
>   [<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@mni.thm.de>
> Fixes: d94a461d7a7d ("ath9k: use ieee80211_tx_status_noskb where possible")
> Cc: <stable@vger.kernel.org> # v4.9
Acked-by: Felix Fietkau <nbd@nbd.name>

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#1545783 — Re: [v2] ath9k: do not return early to fix rcu unlocking

FromKalle Valo <kvalo@qca.qualcomm.com>
Date2016-12-21 15:30 +0100
SubjectRe: [v2] ath9k: do not return early to fix rcu unlocking
Message-ID<sQQ41-4zv-9@gated-at.bofh.it>
In reply to#1541270
Tobias Klausmann <tobias.johannes.klausmann@mni.thm.de> wrote:
> 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:
>  #0:
>   (
>  rcu_read_lock
>  ){......}
>  , 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:
>   <IRQ>
>   [<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
>   <EOI>
>   [<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@mni.thm.de>
> Fixes: d94a461d7a7d ("ath9k: use ieee80211_tx_status_noskb where possible")
> Cc: <stable@vger.kernel.org> # v4.9
> Acked-by: Felix Fietkau <nbd@nbd.name>

Patch applied to ath-current branch of ath.git, thanks.

d1f1c0e289e1 ath9k: do not return early to fix rcu unlocking

-- 
https://patchwork.kernel.org/patch/9472709/

Documentation about submitting wireless patches and checking status
from patchwork:

https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches

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