linux-kernel - Re: [PATCH v2] remoteproc: sysfs/debugfs: fix race while updating recovery flag

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Message-ID: <20230214165016.fteeddbwjjyiwxwb@ripper>
Date:   Tue, 14 Feb 2023 08:50:16 -0800
From:   Bjorn Andersson <andersson@...nel.org>
To:     Satya Durga Srinivasu Prabhala <quic_satyap@...cinc.com>
Cc:     mathieu.poirier@...aro.org, linux-remoteproc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v2] remoteproc: sysfs/debugfs: fix race while updating
 recovery flag

On Tue, Jan 31, 2023 at 09:46:08PM -0800, Satya Durga Srinivasu Prabhala wrote:
> When multiple clients try to update the recovery flag, it is
> 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.
> 

The only query of recovery_disabled that I can see is in
rproc_crash_handler_work(), outside of any lock. So I'm not able to see
the issue you're referring to.

Can you please help me understand better?

Thanks,
Bjorn

> Signed-off-by: Satya Durga Srinivasu Prabhala <quic_satyap@...cinc.com>
> ---
> v1 -> v2:
> - addressed comments from Mukesh Ojha
>   1. take & release lock only while updating recovery flag
>   2. update debugfs
> 
>  drivers/remoteproc/remoteproc_debugfs.c | 4 ++++
>  drivers/remoteproc/remoteproc_sysfs.c   | 4 ++++
>  2 files changed, 8 insertions(+)
> 
> diff --git a/drivers/remoteproc/remoteproc_debugfs.c b/drivers/remoteproc/remoteproc_debugfs.c
> index b86c1d09c70c..2c44d375024e 100644
> --- a/drivers/remoteproc/remoteproc_debugfs.c
> +++ b/drivers/remoteproc/remoteproc_debugfs.c
> @@ -226,10 +226,14 @@ rproc_recovery_write(struct file *filp, const char __user *user_buf,
>  
>  	if (!strncmp(buf, "enabled", count)) {
>  		/* change the flag and begin the recovery process if needed */
> +		mutex_lock(&rproc->lock);
>  		rproc->recovery_disabled = false;
> +		mutex_unlock(&rproc->lock);
>  		rproc_trigger_recovery(rproc);
>  	} else if (!strncmp(buf, "disabled", count)) {
> +		mutex_lock(&rproc->lock);
>  		rproc->recovery_disabled = true;
> +		mutex_unlock(&rproc->lock);
>  	} else if (!strncmp(buf, "recover", count)) {
>  		/* begin the recovery process without changing the flag */
>  		rproc_trigger_recovery(rproc);
> diff --git a/drivers/remoteproc/remoteproc_sysfs.c b/drivers/remoteproc/remoteproc_sysfs.c
> index 8c7ea8922638..628e0de9a132 100644
> --- a/drivers/remoteproc/remoteproc_sysfs.c
> +++ b/drivers/remoteproc/remoteproc_sysfs.c
> @@ -50,10 +50,14 @@ static ssize_t recovery_store(struct device *dev,
>  
>  	if (sysfs_streq(buf, "enabled")) {
>  		/* change the flag and begin the recovery process if needed */
> +		mutex_lock(&rproc->lock);
>  		rproc->recovery_disabled = false;
> +		mutex_unlock(&rproc->lock);
>  		rproc_trigger_recovery(rproc);
>  	} else if (sysfs_streq(buf, "disabled")) {
> +		mutex_lock(&rproc->lock);
>  		rproc->recovery_disabled = true;
> +		mutex_unlock(&rproc->lock);
>  	} else if (sysfs_streq(buf, "recover")) {
>  		/* begin the recovery process without changing the flag */
>  		rproc_trigger_recovery(rproc);
> -- 
> 2.38.1
>