On Mon, 23 Jan 2023 16:53:04 -0500 Steven Rostedt <rost...@goodmis.org> wrote:
> On Mon, 23 Jan 2023 21:50:12 +0100 > Peter Zijlstra <pet...@infradead.org> wrote: > > > 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) <pet...@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; > > > Actually, perhaps we can just add this, and all you need to do is create and set CONFIG_NO_RCU_TRACING (or some other name). This should cover all ftrace locations. (Uncompiled). -- Steve diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h index c303f7a114e9..10ee3fbb9113 100644 --- a/include/linux/trace_recursion.h +++ b/include/linux/trace_recursion.h @@ -135,6 +135,22 @@ extern void ftrace_record_recursion(unsigned long ip, unsigned long parent_ip); # define do_ftrace_record_recursion(ip, pip) do { } while (0) #endif +#ifdef CONFIG_NO_RCU_TRACING +# define trace_warn_on_no_rcu(ip) \ + ({ \ + bool __ret = false; \ + if (!trace_recursion_test(TRACE_RECORD_RECURSION_BIT)) { \ + trace_recursion_set(TRACE_RECORD_RECURSION_BIT); \ + __ret = WARN_ONCE(!rcu_is_watching(), \ + "RCU not on for: %pS\n", (void *)ip); \ + trace_recursion_clear(TRACE_RECORD_RECURSION_BIT); \ + } \ + __ret; \ + }) +#else +# define trace_warn_on_no_rcu(ip) false +#endif + /* * Preemption is promised to be disabled when return bit >= 0. */ @@ -144,6 +160,9 @@ static __always_inline int trace_test_and_set_recursion(unsigned long ip, unsign unsigned int val = READ_ONCE(current->trace_recursion); int bit; + if (trace_warn_on_no_rcu(ip)) + return -1; + bit = trace_get_context_bit() + start; if (unlikely(val & (1 << bit))) { /* _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization