From: Sergei Shtylyov <sergei.shtylyov@gmail.com>
To: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>,
Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Cc: "REE dirk.behme@de.bosch.com" <dirk.behme@de.bosch.com>,
"Shashikant.Suguni@in.bosch.com" <Shashikant.Suguni@in.bosch.com>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"linux-renesas-soc@vger.kernel.org"
<linux-renesas-soc@vger.kernel.org>,
"davem@davemloft.net" <davem@davemloft.net>,
"kuba@kernel.org" <kuba@kernel.org>
Subject: Re: [PATCH/RFC] net: ethernet: ravb: Try to wake subqueue instead of stop on timeout
Date: Sun, 5 Jul 2020 23:28:39 +0300 [thread overview]
Message-ID: <e7e5fd5f-1ed4-7699-1a1f-f4f1bb5495cf@gmail.com> (raw)
In-Reply-To: <TY2PR01MB3692A9F68ACC62E920EE2965D86F0@TY2PR01MB3692.jpnprd01.prod.outlook.com>
Hello!
On 30.06.2020 8:22, Yoshihiro Shimoda wrote:
>>>>>>> From: Yoshihiro Shimoda, Sent: Tuesday, May 26, 2020 6:47 PM
>>>>>>>
>>>>>>> According to the report of [1], this driver is possible to cause
>>>>>>> the following error in ravb_tx_timeout_work().
>>>>>>>
>>>>>>> ravb e6800000.ethernet ethernet: failed to switch device to config mode
>>>>>>>
>>>>>>> This error means that the hardware could not change the state
>>>>>>> from "Operation" to "Configuration" while some tx queue is operating.
>>>>>>> After that, ravb_config() in ravb_dmac_init() will fail, and then
>>>>>>> any descriptors will be not allocaled anymore so that NULL porinter
Pointer. :-)
>>>>>>> dereference happens after that on ravb_start_xmit().
>>>>>>>
>>>>>>> Such a case is possible to be caused because this driver supports
>>>>>>> two queues (NC and BE) and the ravb_stop_dma() is possible to return
>>>>>>> without any stopping process if TCCR or CSR register indicates
>>>>>>> the hardware is operating for TX.
Maybe we should just fix those blind assumptions?
>>>>>>> To fix the issue, just try to wake the subqueue on
>>>>>>> ravb_tx_timeout_work() if the descriptors are not full instead
>>>>>>> of stop all transfers (all queues of TX and RX).
>>>>>>>
>>>>>>> [1]
>>>>>>> https://lore.kernel.org/linux-renesas-soc/20200518045452.2390-1-dirk.behme@de.bosch.com/
>>>>>>>
>>>>>>> Reported-by: Dirk Behme <dirk.behme@de.bosch.com>
>>>>>>> Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
>>>>>>> ---
>>>>>>> I'm guessing that this issue is possible to happen if:
>>>>>>> - ravb_start_xmit() calls netif_stop_subqueue(), and
>>>>>>> - ravb_poll() will not be called with some reason, and
>>>>>>> - netif_wake_subqueue() will be not called, and then
>>>>>>> - dev_watchdog() in net/sched/sch_generic.c calls ndo_tx_timeout().
>>>>>>>
>>>>>>> However, unfortunately, I didn't reproduce the issue yet.
>>>>>>> To be honest, I'm also guessing other queues (SR) of this hardware
>>>>>>> which out-of tree driver manages are possible to reproduce this issue,
>>>>>>> but I didn't try such environment for now...
>>>>>>>
>>>>>>> So, I marked RFC on this patch now.
>>>>>>
>>>>>> I'm afraid, but do you have any comments about this patch?
>>>>>
>>>>> I agree that we should now reset only the stuck queue, not both but I
>>>>> doubt your solution is good enough. Let me have another look...
>>>>
>>>> Thank you for your comment! I hope this solution is good enough...
>>>
>>> I'm sorry again and again. But, do you have any time to look this patch?
>>
>> Yes, in the sense of reviewing -- I don't consider it complete. And no, in
>> the sense of looking into the issue myself... Can we do a per-queue tear-down
>> and re-init (not necessarily all in 1 patch)?
In fact, it would ensue many changes...
> Thank you for your comment! I'm not sure this "re-init" mean. But, we can do
Well, I meant the ring re-allocation and re-formatting... but (looking at
sh_eth) the former is not really necessary, it's enough to just stop the TX
ring and then re-format it and re-start... Well, unfortunately, the way I
structured the code, we can't do *just* that...
> a per-queue tear-down if DMAC is still working. And, we can prepare new descriptors
> for the queue after tear-down.
>
> < Tear-down >
> 1. Set DT_EOS to the desc_bat[queue].
> 2. Set DLR.LBAx to 1.
> 3. Check if DLA.LBAx is cleared.
DLR.LBAx, you mean?
Well, I was thinking of polling TCCR and CSR like the current
ravb_stop_dma() does, but if that works...
> < Prepare new descriptors and start again >
> 4. Prepare new descriptors.
That's where the cause for using the workqueue lies -- the descriptors are
allocated with GFP_KERNEL, not GFP_ATOMIC... if you have time/desire to
untangle all this, I'd appreciate it; else I'd have to work on this in my
copious free time... :-)
> 5. Set DT_LINKFIX to the desc_bat[queue].
> 6. Set DLR.LBAx to 1.
> 7. Check if DLA.LBAx is cleared.
>
>
> I'm thinking doing tear-down and "re-init" of the descriptors is better
> than just try to wake the subqueue. But, what do you think?
Definitely better, yes...
> Best regards,
> Yoshihiro Shimoda
MBR, Sergei
next prev parent reply other threads:[~2020-07-05 20:28 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-26 9:46 [PATCH/RFC] net: ethernet: ravb: Try to wake subqueue instead of stop on timeout Yoshihiro Shimoda
2020-06-15 5:58 ` Yoshihiro Shimoda
2020-06-15 8:12 ` Sergei Shtylyov
2020-06-19 5:46 ` Yoshihiro Shimoda
2020-06-29 5:24 ` Yoshihiro Shimoda
2020-06-29 8:40 ` Sergei Shtylyov
2020-06-29 10:08 ` Yoshihiro Shimoda
2020-06-30 5:22 ` Yoshihiro Shimoda
2020-07-05 20:28 ` Sergei Shtylyov [this message]
2020-07-06 9:25 ` Yoshihiro Shimoda
2020-07-19 19:20 ` Sergei Shtylyov
2020-07-20 1:48 ` Yoshihiro Shimoda
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