Re: [PATCH 3/6] ftrace/x86: Warn and ignore graph tracing when RCU is disabled
flat view
From: Steven Rostedt <rostedt@goodmis.org>
Date: 2023-01-23 21:53:19
Also in:
kvm, linux-pm, lkml, virtualization
On Mon, 23 Jan 2023 21:50:12 +0100 Peter Zijlstra [off-list ref] wrote:
quoted hunk ↗ jump to hunk
All RCU disabled code should be noinstr and hence we should never get here -- when we do, WARN about it and make sure to not actually do tracing. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- arch/x86/kernel/ftrace.c | 3 +++ 1 file changed, 3 insertions(+)--- a/arch/x86/kernel/ftrace.c +++ b/arch/x86/kernel/ftrace.c@@ -646,6 +646,9 @@ void prepare_ftrace_return(unsigned long if (unlikely(atomic_read(¤t->tracing_graph_pause))) return; + if (WARN_ONCE(!rcu_is_watching(), "RCU not on for: %pS\n", (void *)ip)) + return; +
Please add this to after recursion trylock below. Although WARN_ONCE() should not not have recursion issues, as function tracing can do weird things, I rather be safe than sorry, and not have the system triple boot due to some path that might get added in the future. If rcu_is_watching() is false, it will still get by the below recursion check and warn. That is, the below check should be done before this function calls any other function.
bit = ftrace_test_recursion_trylock(ip, *parent); if (bit < 0) return;
-- Steve