linux-kernel - Re: [RFC 1/2] remoteproc: sysfs: authorize rproc shutdown when rproc is crashed

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Date:   Wed, 11 Mar 2020 16:27:07 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Loic Pallardy <loic.pallardy@...com>
Cc:     ohad@...ery.com, mathieu.poirier@...aro.org,
        linux-remoteproc@...r.kernel.org, linux-kernel@...r.kernel.org,
        arnaud.pouliquen@...com, benjamin.gaignard@...aro.org,
        fabien.dessenne@...com, s-anna@...com
Subject: Re: [RFC 1/2] remoteproc: sysfs: authorize rproc shutdown when rproc
 is crashed

On Wed 11 Mar 03:54 PDT 2020, Loic Pallardy wrote:

> When remoteproc recovery is disabled and rproc crashed, user space
> client has no way to reboot co-processor except by a complete platform
> reboot.
> Indeed rproc_shutdown() is called by sysfs state_store() only is rproc
> state is RPROC_RUNNING.
> 
> This patch offers the possibility to shutdown the co-processor if
> it is in RPROC_CRASHED state and so to restart properly co-processor
> from sysfs interface.
> 

I did recently run into a similar problem when I fed my remoteproc
faulty firmware, which lead to it recovering immediately upon boot. The
amount of time spent in !CRASHED state was minimal, so I didn't have any
way to stop the remoteproc.

> Signed-off-by: Loic Pallardy <loic.pallardy@...com>
> ---
>  drivers/remoteproc/remoteproc_core.c  | 2 +-
>  drivers/remoteproc/remoteproc_sysfs.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/remoteproc/remoteproc_core.c b/drivers/remoteproc/remoteproc_core.c
> index 097f33e4f1f3..7ac87a75cd1b 100644
> --- a/drivers/remoteproc/remoteproc_core.c
> +++ b/drivers/remoteproc/remoteproc_core.c
> @@ -1812,7 +1812,7 @@ void rproc_shutdown(struct rproc *rproc)
>  	if (!atomic_dec_and_test(&rproc->power))
>  		goto out;
>  
> -	ret = rproc_stop(rproc, false);
> +	ret = rproc_stop(rproc, rproc->state == RPROC_CRASHED);

Afaict this is unrelated to the problem you're describing in the commit
message.

>  	if (ret) {
>  		atomic_inc(&rproc->power);
>  		goto out;
> diff --git a/drivers/remoteproc/remoteproc_sysfs.c b/drivers/remoteproc/remoteproc_sysfs.c
> index 7f8536b73295..1029458a4678 100644
> --- a/drivers/remoteproc/remoteproc_sysfs.c
> +++ b/drivers/remoteproc/remoteproc_sysfs.c
> @@ -101,7 +101,7 @@ static ssize_t state_store(struct device *dev,
>  		if (ret)
>  			dev_err(&rproc->dev, "Boot failed: %d\n", ret);
>  	} else if (sysfs_streq(buf, "stop")) {
> -		if (rproc->state != RPROC_RUNNING)
> +		if (rproc->state != RPROC_RUNNING && rproc->state != RPROC_CRASHED)

Analogous to the problem reported by Alex here
https://patchwork.kernel.org/patch/11413161/ the handling of stop seems
racy.

In particular, I believe you're failing to protect against a race
with a just scheduled rproc_crash_handler_work() being executed after
the mutex_unlock() in rproc_shutdown()...

With Alex fix that should be less of a problem though...

Regards,
Bjorn

>  			return -EINVAL;
>  
>  		rproc_shutdown(rproc);
> -- 
> 2.7.4
>