ring-buffer: Do not set shortest_full when full target is hit

[ Upstream commit 761d9473e27f0c8782895013a3e7b52a37c8bcfc ]

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.local.home
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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 840301b04f31f334c5bd9270c6eeb30ac9210108..72cebeb0c916f658e3390f903350558c36a5367c 100644 (file)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -970,9 +970,10 @@ 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;