ring-buffer: Have the shortest_full queue be the shortest not longest

commit 702dc9c61e7257d7f477acca7a9d2a4acbd157a9 upstream.

The logic to know when the shortest waiters on the ring buffer should be
woken up or not has uses a less than instead of a greater than compare,
which causes the shortest_full to actually be the longest.

Link: https://lkml.kernel.org/r/20220927231823.718039222@goodmis.org
Cc: stable@vger.kernel.org
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Fixes: 3b1e5cf0237dd ("ring-buffer: Add percentage of ring buffer full to wake up reader")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 708fec4d5df9351a3fbb98e80000c97eac9ec1ff..fd017dd7e43ea67b085b6f2ef57e29cea49d23f2 100644 (file)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -662,7 +662,7 @@ int ring_buffer_wait(struct ring_buffer *buffer, int cpu, int full)
                        nr_pages = cpu_buffer->nr_pages;
                        dirty = ring_buffer_nr_dirty_pages(buffer, cpu);
                        if (!cpu_buffer->shortest_full ||
-                           cpu_buffer->shortest_full < full)
+                           cpu_buffer->shortest_full > full)
                                cpu_buffer->shortest_full = full;
                        raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
                        if (!pagebusy &&