Re: [PATCH V1] rcu-tasks: Fix build error

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Feb 21, 2023 at 02:57:15PM +0530, Srinivasarao Pathipati wrote:
> 
> On 2/21/2023 12:24 AM, Greg KH wrote:
> > On Mon, Feb 20, 2023 at 11:43:59PM +0530, Srinivasarao Pathipati wrote:
> > > Making show_rcu_tasks_rude_gp_kthread() function as 'inline' to
> > > fix below compilation error.
> > > This is applicable to only 5.10 kernels as code got modified
> > > in latest kernels.
> > > 
> > >   In file included from kernel/rcu/update.c:579:0:
> > >   kernel/rcu/tasks.h:710:13: error: ‘show_rcu_tasks_rude_gp_kthread’ defined but not used [-Werror=unused-function]
> > >    static void show_rcu_tasks_rude_gp_kthread(void) {}
> > > 
> > > Signed-off-by: Srinivasarao Pathipati <quic_c_spathi@quicinc.com>
> > > ---
> > >   kernel/rcu/tasks.h | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> > > index 8b51e6a..53ddb4e 100644
> > > --- a/kernel/rcu/tasks.h
> > > +++ b/kernel/rcu/tasks.h
> > > @@ -707,7 +707,7 @@ static void show_rcu_tasks_rude_gp_kthread(void)
> > >   #endif /* #ifndef CONFIG_TINY_RCU */
> > >   #else /* #ifdef CONFIG_TASKS_RUDE_RCU */
> > > -static void show_rcu_tasks_rude_gp_kthread(void) {}
> > > +static inline void show_rcu_tasks_rude_gp_kthread(void) {}
> > >   #endif /* #else #ifdef CONFIG_TASKS_RUDE_RCU */
> > >   ////////////////////////////////////////////////////////////////////////
> > > -- 
> > > 2.7.4
> > > 
> > What commit id caused this problem?
> 
> commit  (8344496e8b49c4122c1808d6cd3f8dc71bccb595 rcu-tasks: Conditionally
> compile show_rcu_tasks_gp_kthreads()) introduced this issue

So this has been around for a very very long time.

Why is this suddenly an issue now, almost 3 years later?  What changed
to cause this to become an issue?

And please put this information in the changelog text.

> This patch added conditional macros for definition of
> show_rcu_tasks_rude_gp_kthread()  but not for dummy definition.
> 
> > And why isn't it an issue in newer kernels, what commit id fixed it and
> > why can't we just take that instead?
> 
> Later code got modified with patch (27c0f1448389 rcutorture: Make
> grace-period kthread report match RCU flavor being tested)  , with this
> there won't be compilation issue.
> 
> This patch is part of below series, Not sure all these can be picked to this
> 5.10 stable branch so fixed issue by simply making function inline.
> 
> if you think it is better to pick this series, please merge to 5.10 branch.
> 
> https://lore.kernel.org/lkml/20201105233900.GA20676@paulmck-ThinkPad-P72/
> 
> [1/4] e1eb075ccf37 rcutorture: Make preemptible TRACE02 enable lockdep
> [2/4] 77dc174103fd rcu-tasks: Convert rcu_tasks_wait_gp() for-loop to
> while-loop
> [3/4] 27c0f1448389 rcutorture: Make grace-period kthread report match RCU
> flavor being tested
> [4/4] 75dc2da5ecd6 rcu-tasks: Make the units of ->init_fract be jiffies

I would need you to test and verify that these actually work properly
and do not cause any regressions and sign off on them before I could
take them.

thanks,

greg k-h