[PATCH v3] rv: Fix multiple definition of __pcpu_unique_da_mon_this

[PATCH v3] rv: Fix multiple definition of __pcpu_unique_da_mon_this

[Mikhail Gavrilov]

The refactoring in commit 30984ccf31b7 ("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: 30984ccf31b7 ("rv: Refactor da_monitor to minimise macros")
Reviewed-by: Gabriele Monaco <gmonaco@redhat.com>
Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
---
Changes since v1: https://lore.kernel.org/all/20260216074727.47292-1-mikhail.v.gavrilov@gmail.com/
- Updated commit message with details on when __pcpu_unique_ uniqueness
  is required (alpha modules, CONFIG_DEBUG_FORCE_WEAK_PER_CPU)
- Added code comment above DA_MON_NAME explaining the rationale

 include/rv/da_monitor.h | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/include/rv/da_monitor.h b/include/rv/da_monitor.h
index db11d41bb438..7511f5464c48 100644
--- a/include/rv/da_monitor.h
+++ b/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);
 	}
 }
-- 
2.53.0

Re: [PATCH v3] rv: Fix multiple definition of __pcpu_unique_da_mon_this

[Gabriele Monaco]

2026-02-16T17:27:23Z Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>:

> The refactoring in commit 30984ccf31b7 ("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.
>

Thanks Mikhail,

there was actually no need to send a v3, I believe Steve's was simply a suggestion for future patches.
(Now actually the reader following the link would wonder if there's any difference since V2, I'm assuming there isn't).

I'm going to take this patch and send it once 7.0-rc1 is out. You don't need to do anything else now.

Cheers,
Gabriele

> Fixes: 30984ccf31b7 ("rv: Refactor da_monitor to minimise macros")
> Reviewed-by: Gabriele Monaco <gmonaco@redhat.com>
> Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
> ---
> Changes since v1: https://lore.kernel.org/all/20260216074727.47292-1-mikhail.v.gavrilov@gmail.com/
> - Updated commit message with details on when __pcpu_unique_ uniqueness
>   is required (alpha modules, CONFIG_DEBUG_FORCE_WEAK_PER_CPU)
> - Added code comment above DA_MON_NAME explaining the rationale
>
> include/rv/da_monitor.h | 16 +++++++++++-----
> 1 file changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/include/rv/da_monitor.h b/include/rv/da_monitor.h
> index db11d41bb438..7511f5464c48 100644
> --- a/include/rv/da_monitor.h
> +++ b/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);
>     }
> }
> --
> 2.53.0