On Wed, Sep 28, 2022 at 04:29:08PM -0400, Steven Rostedt wrote:
> On Wed, 28 Sep 2022 10:59:35 -0400
> Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> > > Will reply with an updated patch.
> >
> > Can you try this patch?
>
> Actually, that failed my testing (for other reasons), can you try this one?
>
Sure, thank you.
> -- Steve
>
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index 3046deacf7b3..46b6f4107428 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -2648,6 +2648,9 @@ rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
> /* Mark the rest of the page with padding */
> rb_event_set_padding(event);
>
> + /* Make sure the padding is visible before the write update */
> + smp_wmb();
> +
> /* Set the write back to the previous setting */
> local_sub(length, &tail_page->write);
> return;
> @@ -2659,6 +2662,9 @@ rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
> /* time delta must be non zero */
> event->time_delta = 1;
>
> + /* Make sure the padding is visible before the tail_page->write update */
> + smp_wmb();
> +
> /* Set write to end of buffer */
> length = (tail + length) - BUF_PAGE_SIZE;
> local_sub(length, &tail_page->write);
> @@ -4627,6 +4633,29 @@ rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
> arch_spin_unlock(&cpu_buffer->lock);
> local_irq_restore(flags);
>
> + /* The writer has preempt disable, wait for it. But not forever */
> + for (nr_loops = 0; nr_loops < 1000; nr_loops++) {
> + /* If the write is past the end of page, a writer is still updating it */
> + if (likely(!reader || rb_page_write(reader) <= BUF_PAGE_SIZE))
> + break;
> +
> + udelay(1);
> +
> + /* Get the latest version of the reader write value */
> + smp_rmb();
> + }
> +
> + /* The writer is not moving forward? Something is wrong */
> + if (RB_WARN_ON(cpu_buffer, nr_loops == 1000))
> + reader = NULL;
> +
> + /*
> + * Make sure we see any padding after the write update
> + * (see rb_reset_tail())
> + */
> + smp_rmb();
> +
> +
> return reader;
> }
>
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