tracing: Fix a warning when allocating buffered events fails

[ Upstream commit 34209fe83ef8404353f91ab4ea4035dbc9922d04 ]

Function trace_buffered_event_disable() produces an unexpected warning
when the previous call to trace_buffered_event_enable() fails to
allocate pages for buffered events.

The situation can occur as follows:

* The counter trace_buffered_event_ref is at 0.

* The soft mode gets enabled for some event and
  trace_buffered_event_enable() is called. The function increments
  trace_buffered_event_ref to 1 and starts allocating event pages.

* The allocation fails for some page and trace_buffered_event_disable()
  is called for cleanup.

* Function trace_buffered_event_disable() decrements
  trace_buffered_event_ref back to 0, recognizes that it was the last
  use of buffered events and frees all allocated pages.

* The control goes back to trace_buffered_event_enable() which returns.
  The caller of trace_buffered_event_enable() has no information that
  the function actually failed.

* Some time later, the soft mode is disabled for the same event.
  Function trace_buffered_event_disable() is called. It warns on
  "WARN_ON_ONCE(!trace_buffered_event_ref)" and returns.

Buffered events are just an optimization and can handle failures. Make
trace_buffered_event_enable() exit on the first failure and left any
cleanup later to when trace_buffered_event_disable() is called.

Link: https://lore.kernel.org/all/20231127151248.7232-2-petr.pavlu@suse.com/
Link: https://lkml.kernel.org/r/20231205161736.19663-3-petr.pavlu@suse.com
Fixes: 0fc1b09ff1ff ("tracing: Use temp buffer when filtering events")
Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index a40d6ba..689d063 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2769,8 +2769,11 @@ void trace_buffered_event_enable(void)
        for_each_tracing_cpu(cpu) {
                page = alloc_pages_node(cpu_to_node(cpu),
                                        GFP_KERNEL | __GFP_NORETRY, 0);
-               if (!page)
-                       goto failed;
+               /* This is just an optimization and can handle failures */
+               if (!page) {
+                       pr_err("Failed to allocate event buffer\n");
+                       break;
+               }
 
                event = page_address(page);
                memset(event, 0, sizeof(*event));
@@ -2784,10 +2787,6 @@ void trace_buffered_event_enable(void)
                        WARN_ON_ONCE(1);
                preempt_enable();
        }
-
-       return;
- failed:
-       trace_buffered_event_disable();
 }
 
 static void enable_trace_buffered_event(void *data)