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

[Paul E. McKenney]

On Mon, Sep 28, 2026 at 10:54:13AM +0800, KunWu Chan wrote:
> 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>

Bradley and Kunwu, are you OK with my applying your tags to the commit
that I am merging this into?

1eccf02fb8d5 ("rcu: Add running and boosted indications to RCU task stall dump")

							Thanx, Paul

> 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
> >
>