netdev - Re: [PATCH/RFC] net: ethernet: ravb: Try to wake subqueue instead of stop on timeout

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Date:   Mon, 15 Jun 2020 11:12:37 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...il.com>
To:     Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        "sergei.shtylyov@...entembedded.com" 
        <sergei.shtylyov@...entembedded.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>
Cc:     "REE dirk.behme@...bosch.com" <dirk.behme@...bosch.com>,
        "Shashikant.Suguni@...bosch.com" <Shashikant.Suguni@...bosch.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH/RFC] net: ethernet: ravb: Try to wake subqueue instead of
 stop on timeout

Hello!

On 15.06.2020 8:58, 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
>> 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.
>>
>> 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@...bosch.com>
>> Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.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...

[...]

MBR, Sergei