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

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Message-ID: <YLBpmdZoGDXNz64y@builder.lan>
Date:   Thu, 27 May 2021 22:55:05 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     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 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.

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
>