rv: Fix multiple definition of __pcpu_unique_da_mon_this

The refactoring in commit 30984cc ("rv: Refactor da_monitor to
minimise macros") replaced per-monitor unique variable names
(da_mon_##name) with a fixed name (da_mon_this).

While this works for 'static' variables (each translation unit gets its
own copy), DEFINE_PER_CPU internally generates a non-static dummy
variable __pcpu_unique_<n> for each per-cpu definition. The requirement
for this variable to be unique although static exists for modules on
specific architectures (alpha) and if the kernel is built with
CONFIG_DEBUG_FORCE_WEAK_PER_CPU (e.g. Fedora's debug kernel).

When multiple per-cpu monitors (e.g. sco and sts) are built-in
simultaneously, they all produce the same __pcpu_unique_da_mon_this
symbol, causing a link error:

  ld: kernel/trace/rv/monitors/sts/sts.o: multiple definition of
      `__pcpu_unique_da_mon_this';
      kernel/trace/rv/monitors/sco/sco.o: first defined here

Fix this by introducing a DA_MON_NAME macro that expands to a
per-monitor unique name (da_mon_<MONITOR_NAME>) via the existing
CONCATENATE helper. This restores the uniqueness that was present
before the refactoring.

Fixes: 30984cc ("rv: Refactor da_monitor to minimise macros")
Reviewed-by: Gabriele Monaco <gmonaco@redhat.com>
Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Link: https://lore.kernel.org/r/20260216172707.1441516-1-mikhail.v.gavrilov@gmail.com
Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>

Author: NTMan

include/rv/da_monitor.h

@@ -20,6 +20,12 @@
 #include <linux/bug.h>
 #include <linux/sched.h>
 
+/*
+ * Per-cpu variables require a unique name although static in some
+ * configurations (e.g. CONFIG_DEBUG_FORCE_WEAK_PER_CPU or alpha modules).
+ */
+#define DA_MON_NAME CONCATENATE(da_mon_, MONITOR_NAME)
+
 static struct rv_monitor rv_this;
 
 static void react(enum states curr_state, enum events event)
@@ -183,14 +189,14 @@ static inline bool da_event(struct da_monitor *da_mon, struct task_struct *tsk,
 /*
  * global monitor (a single variable)
  */
-static struct da_monitor da_mon_this;
+static struct da_monitor DA_MON_NAME;
 
 /*
  * da_get_monitor - return the global monitor address
  */
 static struct da_monitor *da_get_monitor(void)
 {
-	return &da_mon_this;
+	return &DA_MON_NAME;
 }
 
 /*
@@ -223,14 +229,14 @@ static inline void da_monitor_destroy(void) { }
 /*
  * per-cpu monitor variables
  */
-static DEFINE_PER_CPU(struct da_monitor, da_mon_this);
+static DEFINE_PER_CPU(struct da_monitor, DA_MON_NAME);
 
 /*
  * da_get_monitor - return current CPU monitor address
  */
 static struct da_monitor *da_get_monitor(void)
 {
-	return this_cpu_ptr(&da_mon_this);
+	return this_cpu_ptr(&DA_MON_NAME);
 }
 
 /*
@@ -242,7 +248,7 @@ static void da_monitor_reset_all(void)
 	int cpu;
 
 	for_each_cpu(cpu, cpu_online_mask) {
-		da_mon = per_cpu_ptr(&da_mon_this, cpu);
+		da_mon = per_cpu_ptr(&DA_MON_NAME, cpu);
 		da_monitor_reset(da_mon);
 	}
 }