linux-kernel - Re: [PATCH] tracing: Fix to avoid wakeup loop in splice read of per-cpu buffer

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Message-ID: <20230822045937.3fc0da54@rorschach.local.home>
Date:   Tue, 22 Aug 2023 04:59:37 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing: Fix to avoid wakeup loop in splice read of
 per-cpu buffer

On Mon, 21 Aug 2023 23:19:18 +0900
"Masami Hiramatsu (Google)" <mhiramat@...nel.org> wrote:

>  	if (!spd.nr_pages) {
>  		long wait_index;
> +		size_t nr_pages;
> +		size_t full;

size_t is usually considered "long" (machine word length).

>  
>  		if (ret)
>  			goto out;
> @@ -8472,7 +8474,15 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
>  
>  		wait_index = READ_ONCE(iter->wait_index);
>  
> -		ret = wait_on_pipe(iter, iter->tr->buffer_percent);
> +		/* For splice, we have to ensure at least 1 page is filled */
> +		nr_pages = ring_buffer_nr_pages(iter->array_buffer->buffer, iter->cpu_file);
> +		if (nr_pages * iter->tr->buffer_percent < 100) {
> +			full = nr_pages + 99;
> +			do_div(full, nr_pages);

No need for do_div() as full is not 64 bit on 32 bit machines.

That's why the kernel test robot is complaining.

-- Steve

> +		} else
> +			full = iter->tr->buffer_percent;
> +
> +		ret = wait_on_pipe(iter, full);