diff mbox series

Revert "Revert "wifi: ath11k: Enable threaded NAPI""

Message ID 20230809073432.4193-1-johan+linaro@kernel.org
State New
Headers
Series Revert "Revert "wifi: ath11k: Enable threaded NAPI"" |

Commit Message

Johan Hovold Aug. 9, 2023, 7:34 a.m. UTC 
  This reverts commit d265ebe41c911314bd273c218a37088835959fa1.

Disabling threaded NAPI causes the Lenovo ThinkPad X13s to hang (e.g. no
more interrupts received) almost immediately during RX.

Apparently something broke since commit 13aa2fb692d3 ("wifi: ath11k:
Enable threaded NAPI") so that a simple revert is no longer possible.

As commit d265ebe41c91 ("Revert "wifi: ath11k: Enable threaded NAPI"")
does not address the underlying issue reported with QCN9074, it seems we
need to reenable threaded NAPI before fixing both bugs properly.

Fixes: d265ebe41c91 ("Revert "wifi: ath11k: Enable threaded NAPI"")
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
---

Hi Kalle,

Disabling threaded NAPI caused a severe regression in 6.5-rc5 by making
the X13s completely unusable (e.g. no keyboard input, I've seen an RCU
splat once).

I'm supposed to be on holiday this week, but thanks to the rain I gave
rc5 a try and ran into this.

I've added Bjorn, Mani and Konrad on CC who may be able to help with
debugging this further if needed while I'm out-of-office.

Johan


 drivers/net/wireless/ath/ath11k/ahb.c  | 1 +
 drivers/net/wireless/ath/ath11k/pcic.c | 1 +
 2 files changed, 2 insertions(+)

Comments

Manikanta Pubbisetty Aug. 9, 2023, 9:02 a.m. UTC | #1 
On 8/9/2023 1:04 PM, Johan Hovold wrote:
> This reverts commit d265ebe41c911314bd273c218a37088835959fa1.
> 
> Disabling threaded NAPI causes the Lenovo ThinkPad X13s to hang (e.g. no
> more interrupts received) almost immediately during RX.
> 
> Apparently something broke since commit 13aa2fb692d3 ("wifi: ath11k:
> Enable threaded NAPI") so that a simple revert is no longer possible.
> 

This is getting as weird as it would get :)

> As commit d265ebe41c91 ("Revert "wifi: ath11k: Enable threaded NAPI"")
> does not address the underlying issue reported with QCN9074, it seems we
> need to reenable threaded NAPI before fixing both bugs properly.
> 

It seems that the revert has actually solved the issue reported with 
QCN9074.

https://bugzilla.kernel.org/show_bug.cgi?id=217536

We were trying to reproduce the problem on X86+QCN9074 (with threaded 
NAPI) from quite some time, but there is no repro yet.

Actually, enabling/disabling threaded NAPI is a simple affair; I'm 
wondering to hear that interrupts are blocked due  to not having 
threaded NAPI.

What is the chip that Lenovo Thinkpad X13s is having?

Thanks,
Manikanta
Johan Hovold Aug. 9, 2023, 9:16 a.m. UTC | #2 
On Wed, Aug 09, 2023 at 02:32:37PM +0530, Manikanta Pubbisetty wrote:
> On 8/9/2023 1:04 PM, Johan Hovold wrote:
> > This reverts commit d265ebe41c911314bd273c218a37088835959fa1.
> > 
> > Disabling threaded NAPI causes the Lenovo ThinkPad X13s to hang (e.g. no
> > more interrupts received) almost immediately during RX.
> > 
> > Apparently something broke since commit 13aa2fb692d3 ("wifi: ath11k:
> > Enable threaded NAPI") so that a simple revert is no longer possible.
> > 
> 
> This is getting as weird as it would get :)
> 
> > As commit d265ebe41c91 ("Revert "wifi: ath11k: Enable threaded NAPI"")
> > does not address the underlying issue reported with QCN9074, it seems we
> > need to reenable threaded NAPI before fixing both bugs properly.
> > 
> 
> It seems that the revert has actually solved the issue reported with 
> QCN9074.
> 
> https://bugzilla.kernel.org/show_bug.cgi?id=217536

Sure, but it's only a workaround as the underlying cause has not been
identified.

> We were trying to reproduce the problem on X86+QCN9074 (with threaded 
> NAPI) from quite some time, but there is no repro yet.
>
> Actually, enabling/disabling threaded NAPI is a simple affair; I'm 
> wondering to hear that interrupts are blocked due  to not having 
> threaded NAPI.

It sounds to me like the driver's locking is broken if moving to softirq
processing hangs the machine like this. But I have not had time to try
to try to track it down besides verifying that reenabling threaded NAPI
makes the problem go away.

> What is the chip that Lenovo Thinkpad X13s is having?

It's a WCN6855 (QCNFA765).

Johan
Manikanta Pubbisetty Aug. 10, 2023, 4:33 a.m. UTC | #3 
On 8/9/2023 2:46 PM, Johan Hovold wrote:
> On Wed, Aug 09, 2023 at 02:32:37PM +0530, Manikanta Pubbisetty wrote:
>> On 8/9/2023 1:04 PM, Johan Hovold wrote:
>>> This reverts commit d265ebe41c911314bd273c218a37088835959fa1.
>>>
>>> Disabling threaded NAPI causes the Lenovo ThinkPad X13s to hang (e.g. no
>>> more interrupts received) almost immediately during RX.
>>>
>>> Apparently something broke since commit 13aa2fb692d3 ("wifi: ath11k:
>>> Enable threaded NAPI") so that a simple revert is no longer possible.
>>>
>>
>> This is getting as weird as it would get :)
>>
>>> As commit d265ebe41c91 ("Revert "wifi: ath11k: Enable threaded NAPI"")
>>> does not address the underlying issue reported with QCN9074, it seems we
>>> need to reenable threaded NAPI before fixing both bugs properly.
>>>
>>
>> It seems that the revert has actually solved the issue reported with
>> QCN9074.
>>
>> https://bugzilla.kernel.org/show_bug.cgi?id=217536
> 
> Sure, but it's only a workaround as the underlying cause has not been
> identified.
> 
>> We were trying to reproduce the problem on X86+QCN9074 (with threaded
>> NAPI) from quite some time, but there is no repro yet.
>>
>> Actually, enabling/disabling threaded NAPI is a simple affair; I'm
>> wondering to hear that interrupts are blocked due  to not having
>> threaded NAPI.
> 
> It sounds to me like the driver's locking is broken if moving to softirq
> processing hangs the machine like this. But I have not had time to try
> to try to track it down besides verifying that reenabling threaded NAPI
> makes the problem go away.
> 
>> What is the chip that Lenovo Thinkpad X13s is having?
> 
> It's a WCN6855 (QCNFA765).
> 

WCN6855 & QCN9074 share the same driver code base since both being PCIe 
devices. One working and another not working seems to be surprising. Do 
you have a dmesg log when this problem occurred?

We are working on to root cause the original problem. The hindrance as 
of today is that we are not able to repro this so far in Qualcomm. We 
are planning to work with the reporter to get more logs.

Thanks,
Manikanta
Manikanta Pubbisetty Aug. 10, 2023, 4:46 a.m. UTC | #4 
On 8/9/2023 2:46 PM, Johan Hovold wrote:
> On Wed, Aug 09, 2023 at 02:32:37PM +0530, Manikanta Pubbisetty wrote:
>> On 8/9/2023 1:04 PM, Johan Hovold wrote:
>>> This reverts commit d265ebe41c911314bd273c218a37088835959fa1.
>>>
>>> Disabling threaded NAPI causes the Lenovo ThinkPad X13s to hang (e.g. no
>>> more interrupts received) almost immediately during RX.
>>>
>>> Apparently something broke since commit 13aa2fb692d3 ("wifi: ath11k:
>>> Enable threaded NAPI") so that a simple revert is no longer possible.
>>>
>>
>> This is getting as weird as it would get :)
>>
>>> As commit d265ebe41c91 ("Revert "wifi: ath11k: Enable threaded NAPI"")
>>> does not address the underlying issue reported with QCN9074, it seems we
>>> need to reenable threaded NAPI before fixing both bugs properly.
>>>
>>
>> It seems that the revert has actually solved the issue reported with
>> QCN9074.
>>
>> https://bugzilla.kernel.org/show_bug.cgi?id=217536
> 
> Sure, but it's only a workaround as the underlying cause has not been
> identified.
> 
>> We were trying to reproduce the problem on X86+QCN9074 (with threaded
>> NAPI) from quite some time, but there is no repro yet.
>>
>> Actually, enabling/disabling threaded NAPI is a simple affair; I'm
>> wondering to hear that interrupts are blocked due  to not having
>> threaded NAPI.
> 
> It sounds to me like the driver's locking is broken if moving to softirq
> processing hangs the machine like this. But I have not had time to try
> to try to track it down besides verifying that reenabling threaded NAPI
> makes the problem go away.
> 
>> What is the chip that Lenovo Thinkpad X13s is having?
> 
> It's a WCN6855 (QCNFA765).
> 

Also it is worth to give a try with this patch here 
https://patchwork.kernel.org/project/linux-wireless/patch/20230601033840.2997-1-quic_bqiang@quicinc.com/ 
. This seems to be fixing some known interrupt issue on WCN6855. Could 
you pls give a try?

Thanks,
Manikanta
Johan Hovold Aug. 22, 2023, 1:44 p.m. UTC | #5 
On Tue, Aug 22, 2023 at 03:56:24PM +0300, Kalle Valo wrote:
> Johan Hovold <johan@kernel.org> writes:
> > On Wed, Aug 09, 2023 at 09:34:32AM +0200, Johan Hovold wrote:
> >
> >> Disabling threaded NAPI caused a severe regression in 6.5-rc5 by making
> >> the X13s completely unusable (e.g. no keyboard input, I've seen an RCU
> >> splat once).

> > Any chance we can get the offending commit reverted before 6.5 is
> > released? 
> 
> The problem here is that would break QCN9074 again so there is no good
> solution. I suspect we have a fundamental issue in ath11k which we just
> haven't discovered yet. I would prefer to get to the bottom of this
> before reverting anything.

Sure, ideally we can find and fix the underlying issues these next few
days, but since this regression was introduced in rc5 in an attempt to
address the QCN9074 issue which has been there since 6.1 I think we
need to revert otherwise. 

> > I'll take a closer look at this meanwhile.
> 
> Thanks, much appreciated. Did you try enabling all kernel debug
> features, maybe they would give some hints?

Yes, I have a bunch of those enabled. Lockdep does not complain, but the
hard lockup detector triggers and it looks like CPU0 (which handles most
interrupts on this machine currently) has got stuck while processing an
interrupt.

RCU also detects the stall on CPU0 and provides a task dump for
ksoftirqd with the following call trace:

	__switch_to
	run_ksoftirqd
	smpboot_thread_fn
	kthread
	ret_from_fork

I just tried the out-of-tree pseudo NMI series [0] to get a stack trace,
but CPU0 does not respond to those either when I hit this.

Note that it takes a bit of RX to trigger this, but I hit it as soon as
I try to download something substantial (e.g. after a couple of MB).

Johan

[0] https://lore.kernel.org/lkml/20230419225604.21204-1-dianders@chromium.org/
diff mbox series

Patch

diff --git a/drivers/net/wireless/ath/ath11k/ahb.c b/drivers/net/wireless/ath/ath11k/ahb.c
index 139da578831a..1cebba7889d7 100644
--- a/drivers/net/wireless/ath/ath11k/ahb.c
+++ b/drivers/net/wireless/ath/ath11k/ahb.c
@@ -376,6 +376,7 @@  static void ath11k_ahb_ext_irq_enable(struct ath11k_base *ab)
 		struct ath11k_ext_irq_grp *irq_grp = &ab->ext_irq_grp[i];
 
 		if (!irq_grp->napi_enabled) {
+			dev_set_threaded(&irq_grp->napi_ndev, true);
 			napi_enable(&irq_grp->napi);
 			irq_grp->napi_enabled = true;
 		}
diff --git a/drivers/net/wireless/ath/ath11k/pcic.c b/drivers/net/wireless/ath/ath11k/pcic.c
index c63083633b37..c899616fbee4 100644
--- a/drivers/net/wireless/ath/ath11k/pcic.c
+++ b/drivers/net/wireless/ath/ath11k/pcic.c
@@ -466,6 +466,7 @@  void ath11k_pcic_ext_irq_enable(struct ath11k_base *ab)
 		struct ath11k_ext_irq_grp *irq_grp = &ab->ext_irq_grp[i];
 
 		if (!irq_grp->napi_enabled) {
+			dev_set_threaded(&irq_grp->napi_ndev, true);
 			napi_enable(&irq_grp->napi);
 			irq_grp->napi_enabled = true;
 		}