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

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Date:   Mon, 30 Jan 2023 09:43:37 -0800
From:   Satya Durga Srinivasu Prabhala <quic_satyap@...cinc.com>
To:     Mukesh Ojha <quic_mojha@...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 1/30/23 12:03 AM, Mukesh Ojha wrote:
>
> 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 ?
>
Yes, on SMP systems, it is possible that there can be multiple user 
space clients (can simply be fuzzing kind of scripts) which could be 
updating the recovery flag.
>> 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..
Yes, was trying to cover entire function, can be restricted to only when 
recovery flag is being updated as well.
>>
>> 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?
As mentioned above, was trying to cover entire function. Not really 
needed in this case as such.
>
>>           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 ?
>
Thanks, yes. Debug FS needs to be updated too.
> -Mukesh