This is a note to let you know that I've just added the patch titled
tracing: Fix a warning when allocating buffered events fails
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tracing-fix-a-warning-when-allocating-buffered-event.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit babf3836136486e40f2fa3302d5dca692caa64e5
Author: Petr Pavlu <petr.pavlu@xxxxxxxx>
Date: Tue Dec 5 17:17:35 2023 +0100
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@xxxxxxxx/
Link: https://lkml.kernel.org/r/20231205161736.19663-3-petr.pavlu@xxxxxxxx
Fixes: 0fc1b09ff1ff ("tracing: Use temp buffer when filtering events")
Signed-off-by: Petr Pavlu <petr.pavlu@xxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index a40d6baf101f0..689d063dd2062 100644
--- 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)
