linux-kernel - Re: [PATCH] remoteproc: sysfs: fix race while updating recovery flag

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Message-ID: <d9708f4b-e533-e400-acbf-3d8e816f242e@quicinc.com>
Date:   Mon, 30 Jan 2023 13:33:42 +0530
From:   Mukesh Ojha <quic_mojha@...cinc.com>
To:     Satya Durga Srinivasu Prabhala <quic_satyap@...cinc.com>,
        <andersson@...nel.org>, <mathieu.poirier@...aro.org>
CC:     <linux-remoteproc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH] remoteproc: sysfs: fix race while updating recovery flag


On 1/30/2023 4:21 AM, Satya Durga Srinivasu Prabhala wrote:
> When multiple clients try to update the recovery flag, it is

Multiple user-space clients ?

> possible that, race condition would lead to undesired results
> as updates to recovery flag isn't protected by any mechanism
> today. To avoid such issues, take remoteproc mutex lock before
> updating recovery flag and release the lock once done.

But your patch also adds locks for the case which does not update 
recovery flag..

> 
> Signed-off-by: Satya Durga Srinivasu Prabhala <quic_satyap@...cinc.com>
> ---
>   drivers/remoteproc/remoteproc_sysfs.c | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/remoteproc/remoteproc_sysfs.c b/drivers/remoteproc/remoteproc_sysfs.c
> index 8c7ea8922638..ec37176e1589 100644
> --- a/drivers/remoteproc/remoteproc_sysfs.c
> +++ b/drivers/remoteproc/remoteproc_sysfs.c
> @@ -48,16 +48,21 @@ static ssize_t recovery_store(struct device *dev,
>   {
>   	struct rproc *rproc = to_rproc(dev);
>   
> +	mutex_lock(&rproc->lock);
>   	if (sysfs_streq(buf, "enabled")) {
>   		/* change the flag and begin the recovery process if needed */
>   		rproc->recovery_disabled = false;
> +		mutex_unlock(&rproc->lock);
>   		rproc_trigger_recovery(rproc);
>   	} else if (sysfs_streq(buf, "disabled")) {
>   		rproc->recovery_disabled = true;
> +		mutex_unlock(&rproc->lock);
>   	} else if (sysfs_streq(buf, "recover")) {
>   		/* begin the recovery process without changing the flag */
> +		mutex_unlock(&rproc->lock);

is it really needed for this case?

>   		rproc_trigger_recovery(rproc);
>   	} else {
> +		mutex_unlock(&rproc->lock);

same here..

>   		return -EINVAL;
>   	}
>   

Do you also need to add lock for rproc_recovery_write in 
drivers/remoteproc/remoteproc_debugfs.c ?

-Mukesh