From: Steven Rostedt (VMware) <[email protected]> commit b40341fad6cc2daa195f8090fd3348f18fff640a upstream.
The first thing that the ftrace function callback helper functions should do is to check for recursion. Peter Zijlstra found that when "rcu_is_watching()" had its notrace removed, it caused perf function tracing to crash. This is because the call of rcu_is_watching() is tested before function recursion is checked and and if it is traced, it will cause an infinite recursion loop. rcu_is_watching() should still stay notrace, but to prevent this should never had crashed in the first place. The recursion prevention must be the first thing done in callback functions. Link: https://lore.kernel.org/r/[email protected] Cc: [email protected] Cc: Paul McKenney <[email protected]> Fixes: c68c0fa293417 ("ftrace: Have ftrace_ops_get_func() handle RCU and PER_CPU flags too") Acked-by: Peter Zijlstra (Intel) <[email protected]> Reported-by: Peter Zijlstra (Intel) <[email protected]> Signed-off-by: Steven Rostedt (VMware) <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- kernel/trace/ftrace.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -6159,17 +6159,15 @@ static void ftrace_ops_assist_func(unsig { int bit; - if ((op->flags & FTRACE_OPS_FL_RCU) && !rcu_is_watching()) - return; - bit = trace_test_and_set_recursion(TRACE_LIST_START, TRACE_LIST_MAX); if (bit < 0) return; preempt_disable_notrace(); - if (!(op->flags & FTRACE_OPS_FL_PER_CPU) || - !ftrace_function_local_disabled(op)) { + if ((!(op->flags & FTRACE_OPS_FL_RCU) || rcu_is_watching()) && + (!(op->flags & FTRACE_OPS_FL_PER_CPU) || + !ftrace_function_local_disabled(op))) { op->func(ip, parent_ip, op, regs); }
