Re: [PATCH] rcu: include rtmutex_common.h in tree_stall.h

[KunWu Chan]

Thanks, Arnd.

Tested on top of 1eccf02fb8d5 with CONFIG_PREEMPT_RCU=y:

CONFIG_RT_MUTEXES=y: build passes
CONFIG_RT_MUTEXES=n: fails without this patch, passes with it

The failure is in tree_stall.h, where rt_mutex_owner() is used
before tree_plugin.h includes rtmutex_common.h. This matches the
reported failure, and the added include fixes it.

Reviewed-by: Kunwu Chan <kunwu.chan@xxxxxxxxx>
Tested-by: Kunwu Chan <kunwu.chan@xxxxxxxxx>

Thanks,
Kunwu

On Fri, Sep 25, 2026 at 9:39 PM Arnd Bergmann <arnd@xxxxxxxxxx> wrote:
>
> From: Arnd Bergmann <arnd@xxxxxxxx>
>
> The added call to rt_mutex_owner() makes this fail to build in
> some configurations:
>
> In file included from kernel/rcu/tree.c:5121:
> kernel/rcu/tree_stall.h:333:8: error: call to undeclared function 'rt_mutex_owner'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
>   333 |                         if (rt_mutex_owner(&rnp->boost_mtx.rtmutex) == t)
>       |                             ^
> kernel/rcu/tree_stall.h:333:48: error: comparison between pointer and integer ('int' and 'struct task_struct *') [-Werror,-Wpointer-integer-compare]
>   333 |                         if (rt_mutex_owner(&rnp->boost_mtx.rtmutex) == t)
>       |                             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^  ~
> In file included from kernel/rcu/tree.c:5124:
> In file included from kernel/rcu/tree_plugin.h:14:
> kernel/rcu/../locking/rtmutex_common.h:231:35: error: conflicting types for 'rt_mutex_owner'
>   231 | static inline struct task_struct *rt_mutex_owner(struct rt_mutex_base *lock)
>       |                                   ^
> kernel/rcu/tree_stall.h:333:8: note: previous implicit declaration is here
>   333 |                         if (rt_mutex_owner(&rnp->boost_mtx.rtmutex) == t)
>       |                             ^
>
> There are already a couple of inclusions of "../locking/rtmutex_common.h",
> so assume this is safe to do here.
>
> Fixes: 1eccf02fb8d5 ("rcu: Add running and boosted indications to RCU task stall dump")
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
> I wonder if it would be better to either move the rt_mutex_owner()
> definition into a global header like include/linux/rtmutex.h, or to
> move the code out of tree_stall.h into a .c file, as this feels like a
> layering violation.
> ---
>  kernel/rcu/tree_stall.h | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
> index 5dded1e89197..803a56af3259 100644
> --- a/kernel/rcu/tree_stall.h
> +++ b/kernel/rcu/tree_stall.h
> @@ -12,6 +12,7 @@
>  #include <linux/rcu_notifier.h>
>  #include <linux/smp.h>
>  #include <linux/rtmutex.h>
> +#include "../locking/rtmutex_common.h"
>
>  //////////////////////////////////////////////////////////////////////////////
>  //
> --
> 2.53.0
>