On 7/20/22 19:02, Steven Rostedt wrote:
> On Wed, 20 Jul 2022 18:50:39 +0200
> Daniel Bristot de Oliveira <bristot@xxxxxxxxxx> wrote:
>
>> On 7/20/22 18:41, Steven Rostedt wrote:
>>> On Tue, 19 Jul 2022 19:27:07 +0200
>>> Daniel Bristot de Oliveira <bristot@xxxxxxxxxx> wrote:
>>>
>>>> +/*
>>>> + * reacting_on interface.
>>>> + */
>>>> +static ssize_t reacting_on_read_data(struct file *filp,
>>>> + char __user *user_buf,
>>>> + size_t count, loff_t *ppos)
>>>> +{
>>>> + char *buff;
>>>> +
>>>> + mutex_lock(&rv_interface_lock);
>>>> + buff = reacting_on ? "1\n" : "0\n";
>>>> + mutex_unlock(&rv_interface_lock);
>>> Again, no need for the locks, but perhaps just to keep things sane:
>>>
>>> buf = READ_ONCE(reacting_on) ? "1\n" : "0\n";
>>
>> So, for all files that only read/write a single variable, use READ_ONCE/WRITE_ONCE without
>> locks? (and in all usage of that variable too).
>
> Only if there's no races.
>
> That is, taking the locks here provide no benefit over a READ_ONCE().
>
> If there was some logic that checks if the value is still valid or not,
> then that would be a different story.
>
> For example:
>
> static int enable_monitor(struct rv_monitor_def *mdef)
> {
> int retval;
>
> if (!mdef->monitor->enabled) {
> retval = mdef->monitor->enable();
> if (retval)
> return retval;
> }
>
> mdef->monitor->enabled = 1;
>
> return 0;
> }
>
> That has logic that looks to require a lock to protect things from changing
> from underneath.
ack, so the only variable I see we can use READ_ONCE/WRITE_ONCE is the reacting_on...
-- Daniel
>
> -- Steve
