From: "Steven Rostedt (Google)" rostedt@goodmis.org

The rb_watermark_hit() checks if the amount of data in the ring buffer is above the percentage level passed in by the "full" variable. If it is, it returns true.

But it also sets the "shortest_full" field of the cpu_buffer that informs writers that it needs to call the irq_work if the amount of data on the ring buffer is above the requested amount.

The rb_watermark_hit() always sets the shortest_full even if the amount in the ring buffer is what it wants. As it is not going to wait, because it has what it wants, there's no reason to set shortest_full.

Link: https://lore.kernel.org/linux-trace-kernel/20240312115641.6aa8ba08@gandalf.l...

Cc: stable@vger.kernel.org Cc: Mathieu Desnoyers mathieu.desnoyers@efficios.com Fixes: 42fb0a1e84ff5 ("tracing/ring-buffer: Have polling block on watermark") Reviewed-by: Masami Hiramatsu (Google) mhiramat@kernel.org Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org --- kernel/trace/ring_buffer.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index aa332ace108b..6ffbccb9bcf0 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -834,9 +834,10 @@ static bool rb_watermark_hit(struct trace_buffer *buffer, int cpu, int full) pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page; ret = !pagebusy && full_hit(buffer, cpu, full);

- if (!cpu_buffer->shortest_full || - cpu_buffer->shortest_full > full) - cpu_buffer->shortest_full = full; + if (!ret && (!cpu_buffer->shortest_full || + cpu_buffer->shortest_full > full)) { + cpu_buffer->shortest_full = full; + } raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); } return ret;