5.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Petr Pavlu petr.pavlu@suse.com
[ 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 --- kernel/trace/trace.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index a15dffe60722f..b8030f1e577bb 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -2438,8 +2438,11 @@ 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)); @@ -2453,10 +2456,6 @@ 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)