Re: [PATCH 4/6] tracing: Fix waking up tracing readers

[Steven Rostedt <rostedt@goodmis.org>]

On Fri, 08 Mar 2024 13:38:20 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> +static DEFINE_MUTEX(wait_mutex);
> +
> +static bool wait_woken_prepare(struct trace_iterator *iter, int *wait_index)
> +{
> +	bool woken = false;
> +
> +	mutex_lock(&wait_mutex);
> +	if (iter->waking)
> +		woken = true;
> +	*wait_index = iter->wait_index;
> +	mutex_unlock(&wait_mutex);
> +
> +	return woken;
> +}

The last patch adds this code after a prepare_to_wait(), which triggered
the warning:

  do not call blocking ops when !TASK_RUNNING; state=1 set at [<00000000797e3e20>] prepare_to_wait+0x48/0xf0

Which is correct. The prepare_to_wait() set task state to
TASK_INTERRUPTIBLE, so I can not call a mutex after that.

I'll send a v2 where I switch this over to spin locks.

-- Steve


> +
> +static bool wait_woken_check(struct trace_iterator *iter, int *wait_index)
> +{
> +	bool woken = false;
> +
> +	mutex_lock(&wait_mutex);
> +	if (iter->waking || *wait_index != iter->wait_index)
> +		woken = true;
> +	mutex_unlock(&wait_mutex);
> +
> +	return woken;
> +}
> +
> +static void wait_woken_set(struct trace_iterator *iter)
> +{
> +	mutex_lock(&wait_mutex);
> +	iter->waking++;
> +	iter->wait_index++;
> +	mutex_unlock(&wait_mutex);
> +}
> +
> +static void wait_woken_clear(struct trace_iterator *iter)
> +{
> +	mutex_lock(&wait_mutex);
> +	iter->waking--;
> +	mutex_unlock(&wait_mutex);
> +}
> +