linux-kernel - Re: [PATCH 1/1] remoteproc: use freezable workqueue for crash notifications

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Message-ID: <be4ea351-7144-8b53-6fd7-6a2204e0040d@codeaurora.org>
Date:   Fri, 28 May 2021 17:12:08 -0700
From:   Siddharth Gupta <sidgup@...eaurora.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Alex Elder <elder@...aro.org>
Cc:     ohad@...ery.com, mathieu.poirier@...aro.org,
        linux-remoteproc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] remoteproc: use freezable workqueue for crash
 notifications


On 5/27/2021 8:55 PM, Bjorn Andersson wrote:
> On Wed 19 May 18:44 CDT 2021, Alex Elder wrote:
>
>> When a remoteproc has crashed, rproc_report_crash() is called to
>> handle whatever recovery is desired.  This can happen at almost any
>> time, often triggered by an interrupt, though it can also be
>> initiated by a write to debugfs file remoteproc/remoteproc*/crash.
>>
>> When a crash is reported, the crash handler worker is scheduled to
>> run (rproc_crash_handler_work()).  One thing that worker does is
>> call rproc_trigger_recovery(), which calls rproc_stop().  That calls
>> the ->stop method for any remoteproc subdevices before making the
>> remote processor go offline.
>>
>> The Q6V5 modem remoteproc driver implements an SSR subdevice that
>> notifies registered drivers when the modem changes operational state
>> (prepare, started, stop/crash, unprepared).  The IPA driver
>> registers to receive these notifications.
>>
>> With that as context, I'll now describe the problem.
>>
>> There was a situation in which buggy modem firmware led to a modem
>> crash very soon after system (AP) resume had begun.  The crash caused
>> a remoteproc SSR crash notification to be sent to the IPA driver.
>> The problem was that, although system resume had begun, it had not
>> yet completed, and the IPA driver was still in a suspended state.
>>
>> This scenario could happen to any driver that registers for these
>> SSR notifications, because they are delivered without knowledge of
>> the (suspend) state of registered recipient drivers.
>>
>> This patch offers a simple fix for this, by having the crash
>> handling worker function run on the system freezable workqueue.
>> This workqueue does not operate if user space is frozen (for
>> suspend).  As a result, the SSR subdevice only delivers its
>> crash notification when the system is fully operational (i.e.,
>> neither suspended nor in suspend/resume transition).
>>
> This makes sense to me; both that it ensures that we spend our resources
> on the actual system resume and that it avoids surprises from this
> happening while the system still is in a funky state...
>
> Reviewed-by: Bjorn Andersson <bjorn.andersson@...aro.org>
>
> But it would be nice to get some input from other users of the
> framework.
This patch sounds like a good idea for cases where the
request_firmware() APIs fallback to userspace firmware loading.

Will test out this patch and report back.

Thanks,
Sid
>
> Regards,
> Bjorn
>
>> Signed-off-by: Alex Elder <elder@...aro.org>
>> ---
>>   drivers/remoteproc/remoteproc_core.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/remoteproc/remoteproc_core.c b/drivers/remoteproc/remoteproc_core.c
>> index 39cf44cb08035..6bedf2d2af239 100644
>> --- a/drivers/remoteproc/remoteproc_core.c
>> +++ b/drivers/remoteproc/remoteproc_core.c
>> @@ -2724,8 +2724,8 @@ void rproc_report_crash(struct rproc *rproc, enum rproc_crash_type type)
>>   	dev_err(&rproc->dev, "crash detected in %s: type %s\n",
>>   		rproc->name, rproc_crash_to_string(type));
>>   
>> -	/* create a new task to handle the error */
>> -	schedule_work(&rproc->crash_handler);
>> +	/* Have a worker handle the error; ensure system is not suspended */
>> +	queue_work(system_freezable_wq, &rproc->crash_handler);
>>   }
>>   EXPORT_SYMBOL(rproc_report_crash);
>>   
>> -- 
>> 2.27.0
>>