xeon08: Enable lttng lockdep tracepoints

xeon08/configuration.nix

@@ -18,6 +18,10 @@
   # disable automatic garbage collector
   nix.gc.automatic = lib.mkForce false;
 
+  # members of the tracing group can use the lttng-provided kernel events
+  # without root permissions
+  users.groups.tracing.members = [ "arocanon" ];
+
   # set up both ethernet and infiniband ips
   networking = {
     hostName = "xeon08";

xeon08/kernel/lttng.nix

@@ -2,12 +2,23 @@
 
 let
 
-  # the lttng btrfs probe crashes at compile time because of an undefined
+  # The lttng btrfs probe crashes at compile time because of an undefined
   # function. This disables the btrfs tracepoints to avoid the issue.
+
+  # Also enable lockdep tracepoints, this is disabled by default because it
+  # does not work well on architectures other than x86_64 (i think that arm) as
+  # I was told on the mailing list.
   lttng-modules-fixed = config.boot.kernelPackages.lttng-modules.overrideAttrs (finalAttrs: previousAttrs: {
     patchPhase = (lib.optionalString (previousAttrs ? patchPhase) previousAttrs.patchPhase) + ''
+      # disable btrfs
       substituteInPlace src/probes/Kbuild \
         --replace "  obj-\$(CONFIG_LTTNG) += lttng-probe-btrfs.o" "  #obj-\$(CONFIG_LTTNG) += lttng-probe-btrfs.o"
+
+      # enable lockdep tracepoints
+      substituteInPlace src/probes/Kbuild \
+        --replace "#ifneq (\$(CONFIG_LOCKDEP),)"                  "ifneq (\$(CONFIG_LOCKDEP),)" \
+        --replace "#  obj-\$(CONFIG_LTTNG) += lttng-probe-lock.o" "  obj-\$(CONFIG_LTTNG) += lttng-probe-lock.o" \
+        --replace "#endif # CONFIG_LOCKDEP"                       "endif # CONFIG_LOCKDEP"
     '';
   });
 in {
@@ -29,8 +40,4 @@ in {
       '';
     };
   };
-
-  # members of the tracing group can use the lttng-provided kernel events
-  # without root permissions
-  users.groups.tracing.members = [ "arocanon" ];
 }