On Fri, 24 May 2024 22:37:02 -0400 Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx> > > Allow for instances to have their own ftrace_ops part of the fgraph_ops > that makes the funtion_graph tracer filter on the set_ftrace_filter file > of the instance and not the top instance. > > Note that this also requires to update ftrace_graph_func() to call new > function_graph_enter_ops() instead of function_graph_enter() so that > it avoid pushing on shadow stack multiple times on the same function. So I found a major design flaw in this patch. > > Co-developed with Masami Hiramatsu: > Link: https://lore.kernel.org/linux-trace-kernel/171509102088.162236.15758883237657317789.stgit@devnote2 > > Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx> > Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx> > --- > diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c > index 8da0e66ca22d..998558cb8f15 100644 > --- a/arch/x86/kernel/ftrace.c > +++ b/arch/x86/kernel/ftrace.c > @@ -648,9 +648,24 @@ void ftrace_graph_func(unsigned long ip, unsigned long parent_ip, > struct ftrace_ops *op, struct ftrace_regs *fregs) > { > struct pt_regs *regs = &fregs->regs; > - unsigned long *stack = (unsigned long *)kernel_stack_pointer(regs); > + unsigned long *parent = (unsigned long *)kernel_stack_pointer(regs); > + struct fgraph_ops *gops = container_of(op, struct fgraph_ops, ops); > + int bit; > + > + if (unlikely(ftrace_graph_is_dead())) > + return; > + > + if (unlikely(atomic_read(¤t->tracing_graph_pause))) > + return; > > - prepare_ftrace_return(ip, (unsigned long *)stack, 0); > + bit = ftrace_test_recursion_trylock(ip, *parent); > + if (bit < 0) > + return; > + > + if (!function_graph_enter_ops(*parent, ip, 0, parent, gops)) So each registered graph ops has its own ftrace_ops which gets registered with ftrace, so this function does get called in a loop (by the ftrace iterator function). This means that we would need that code to detect the function_graph_enter_ops() getting called multiple times for the same function. This means each fgraph_ops gits its own retstack on the shadow stack. I find this a waste of shadow stack resources, and also complicates the code with having to deal with tail calls and all that. BUT! There's good news! I also thought about another way of handling this. I have something working, but requires a bit of rewriting the code. I should have something out in a day or two. -- Steve > + *parent = (unsigned long)&return_to_handler; > + > + ftrace_test_recursion_unlock(bit); > } > #endif >
