Messages in this thread | | | Date | Sun, 4 Nov 2018 09:06:49 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH] tracing/fgraph: remove unnecessary unlikely() |
| |
On Sat, 3 Nov 2018 22:35:37 -0400 Yangtao Li <tiny.windzz@gmail.com> wrote:
> WARN_ON() already contains an unlikely(), so it's not necessary to use > unlikely.
NACK... see below.
> > Signed-off-by: Yangtao Li <tiny.windzz@gmail.com> > --- > kernel/trace/trace_functions_graph.c | 6 ++---- > 1 file changed, 2 insertions(+), 4 deletions(-) > > diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c > index 169b3c44ee97..f8c2a08e4985 100644 > --- a/kernel/trace/trace_functions_graph.c > +++ b/kernel/trace/trace_functions_graph.c > @@ -201,9 +201,8 @@ ftrace_pop_return_trace(struct ftrace_graph_ret *trace, unsigned long *ret, > if (index < 0) > index += FTRACE_NOTRACE_DEPTH; > > - if (unlikely(index < 0 || index >= FTRACE_RETFUNC_DEPTH)) { > + if (WARN_ON(index < 0 || index >= FTRACE_RETFUNC_DEPTH)) {
When function graph is enabled, the printk from the warn on will likely be traced as well and trigger the same WARN_ON, which will again cause a recursion loop and crash and reboot the box with no output at all.
> ftrace_graph_stop();
Notice that I call ftrace_graph_stop() *before* the WARN_ON(). This disables the ftrace graph tracer and prevents the recursion loop from happening.
There's a reason that the WARN_ON() is placed where it is.
But thanks for the report, it shows that I need to add a comment here so that someone else doesn't send a similar patch in the future.
-- Steve
> - WARN_ON(1); > /* Might as well panic, otherwise we have no where to go */ > *ret = (unsigned long)panic; > return; > @@ -274,9 +273,8 @@ unsigned long ftrace_return_to_handler(unsigned long frame_pointer) > */ > ftrace_graph_return(&trace); > > - if (unlikely(!ret)) { > + if (WARN_ON(!ret)) { > ftrace_graph_stop(); > - WARN_ON(1); > /* Might as well panic. What else to do? */ > ret = (unsigned long)panic; > }
| |