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?
-- 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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