On Fri, 31 May 2024 02:03:46 -0400 Steven Rostedt <rost...@goodmis.org> wrote:
> On Fri, 31 May 2024 12:12:41 +0900 > Masami Hiramatsu (Google) <mhira...@kernel.org> wrote: > > > On Thu, 30 May 2024 22:30:57 -0400 > > Steven Rostedt <rost...@goodmis.org> wrote: > > > > > On Fri, 24 May 2024 22:37:02 -0400 > > > Steven Rostedt <rost...@goodmis.org> wrote: > > > > > > > From: "Steven Rostedt (VMware)" <rost...@goodmis.org> > > > > > > > > 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) <rost...@goodmis.org> > > > > Signed-off-by: Masami Hiramatsu (Google) <mhira...@kernel.org> > > > > Signed-off-by: Steven Rostedt (Google) <rost...@goodmis.org> > > > > --- > > > > > > > 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. > > > > Ah, that is my concern and the reason why I added bitmap and stack reuse > > code in the ftrace_push_return_trace(). > > > > > > > > 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. > > > > Hmm, I just wonder why you don't reocver my bitmap check and stack > > reusing code. Are there any problem on it? (Too complicated?) > > > > I actually dislike the use of ftrace itself to do the loop. I rather > have fgraph be in control of it. (actually, I agreed with you, looping in ftrace may cause trouble) > > I've come up with a new "subops" assignment, where you can have one > ftrace_ops represent multiple sub ftrace_ops. Basically, each fgraph > ops can register its own ftrace_ops under a single graph_ops > ftrace_ops. The graph_ops will be used to decide what functions call > the callback, and then the callback does the multiplexing. So is it similar to the fprobe/kprobe, use shared signle ftrace_ops, but keep each fgraph has own hash table? > This removes the need to touch the architecture code. It can also be > used by fprobes to handle the attachments to functions for several > different sets of callbacks. > > I'll send out patches soon. OK, I'll wait for that. Thank you! > > -- Steve > -- Masami Hiramatsu (Google) <mhira...@kernel.org>
