On Thu, 22 Jan 2015 12:58:00 -0800 Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > On Thu, Jan 22, 2015 at 12:37 PM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > On Thu, 22 Jan 2015 12:24:47 -0800 > > Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > > > >> > Also, please remove the "notrace", because function tracing goes an > >> > extra step to not require RCU being visible. The only thing you get > >> > with notrace is not being able to trace an otherwise traceable function. > >> > > >> > >> Is this also true for kprobes? And can kprobes nest inside function > >> tracing hooks? > > > > No, kprobes are a bit more fragile than function tracing or tracepoints. > > > > And nothing should nest inside a function hook (except for interrupts, > > they are fine). > > > > But kprobes do nest inside interrupts, right? A kprobe being called while a function trace is happening is fine, but you should not have the kprobe set directly inside the function trace callback code. Because that means a kprobe could happen anywhere function tracing is happening (for instance, in NMI context). > > >> > >> The other issue, above and beyond RCU, is that we can't let kprobes > >> run on the int3 stack. If Xen upcalls can happen when interrupts are > >> off, then we may need this protection to prevent that type of > >> recursion. (This will be much less scary in 3.20, because userspace > >> int3 instructions will no longer execute on the int3 stack.) > > > > Does this execute between the start of the int3 interrupt handler and > > the call of do_int3()? > > I doubt it. > > The thing I worry about is that, if do_int3 nests inside itself by any > means (e.g. int3 sends a signal, scheduling for whatever reason > (really shouldn't happen, but I haven't looked that hard)), then we're > completely hosed -- the inner int3 will overwrite the outer int3's > stack frame. Since I have no idea what Xen upcalls do, I don't know > whether they can fire inside do_int3. I thought there's logic in the do_int3 handler (in the assembly code) that can handle nested int3s. I'm not sure what xen does though. -- Steve -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
