From: Lai Jiangshan <jiangshan.ljs@antgroup.com>

Prepare for arch-specific-defined rcu_preempt_depth_set().

No functionality change intended, but it has to be defined as a macro
as rcupdate.h is a very low level header included from areas that don't
even know about the task struct "current".

Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
---
 include/linux/rcupdate.h | 1 +
 kernel/rcu/tree_plugin.h | 5 -----
 2 files changed, 1 insertion(+), 5 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 16f519914415..210f65baf47c 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -78,6 +78,7 @@ void __rcu_read_unlock(void);
  * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
  */
 #define rcu_preempt_depth() READ_ONCE(current->rcu_read_lock_nesting)
+#define rcu_preempt_depth_set(val) WRITE_ONCE(current->rcu_read_lock_nesting, (val))
 
 #else /* #ifdef CONFIG_PREEMPT_RCU */
 
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 36a8b5dbf5b5..b1264096d03a 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -387,11 +387,6 @@ static int rcu_preempt_read_exit(void)
 	return ret;
 }
 
-static void rcu_preempt_depth_set(int val)
-{
-	WRITE_ONCE(current->rcu_read_lock_nesting, val);
-}
-
 /*
  * Preemptible RCU implementation for rcu_read_lock().
  * Just increment ->rcu_read_lock_nesting, shared state will be updated
-- 
2.19.1.6.gb485710b

> On Mar 28, 2024, at 1:20 PM, Lai Jiangshan <jiangshanlai@gmail.com> wrote:
> 
> From: Lai Jiangshan <jiangshan.ljs@antgroup.com>
> 
> Prepare for arch-specific-defined rcu_preempt_depth_set().
> 
> No functionality change intended, but it has to be defined as a macro
> as rcupdate.h is a very low level header included from areas that don't
> even know about the task struct "current".

Sorry I did not follow changelog. If some rcupdate.h includers do not know
about task_struct, how does adding a macro that uses current help?

Thanks,

 - Joel

> 
> Cc: "Paul E. McKenney" <paulmck@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Frederic Weisbecker <frederic@kernel.org>
> Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
> ---
> include/linux/rcupdate.h | 1 +
> kernel/rcu/tree_plugin.h | 5 -----
> 2 files changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 16f519914415..210f65baf47c 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -78,6 +78,7 @@ void __rcu_read_unlock(void);
>  * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
>  */
> #define rcu_preempt_depth() READ_ONCE(current->rcu_read_lock_nesting)
> +#define rcu_preempt_depth_set(val) WRITE_ONCE(current->rcu_read_lock_nesting, (val))
> 
> #else /* #ifdef CONFIG_PREEMPT_RCU */
> 
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 36a8b5dbf5b5..b1264096d03a 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -387,11 +387,6 @@ static int rcu_preempt_read_exit(void)
>    return ret;
> }
> 
> -static void rcu_preempt_depth_set(int val)
> -{
> -    WRITE_ONCE(current->rcu_read_lock_nesting, val);
> -}
> -
> /*
>  * Preemptible RCU implementation for rcu_read_lock().
>  * Just increment ->rcu_read_lock_nesting, shared state will be updated
> --
> 2.19.1.6.gb485710b
> 

On Sun, Mar 31, 2024 at 7:10 PM Joel Fernandes <joel@joelfernandes.org> wrote:
>
>
>
> > On Mar 28, 2024, at 1:20 PM, Lai Jiangshan <jiangshanlai@gmail.com> wrote:
> >
> > From: Lai Jiangshan <jiangshan.ljs@antgroup.com>
> >
> > Prepare for arch-specific-defined rcu_preempt_depth_set().
> >
> > No functionality change intended, but it has to be defined as a macro
> > as rcupdate.h is a very low level header included from areas that don't
> > even know about the task struct "current".
>
> Sorry I did not follow changelog. If some rcupdate.h includers do not know
> about task_struct, how does adding a macro that uses current help?
>

Hello

This is how macro works and it expands blindly based on tokens on the
usage-sites.

And rcu_preempt_depth() & rcu_preempt_depth_set() are not universally
used wrappers, the user can simply also include linux/sched.h to make
they work.

Thanks
Lai

2024年4月1日 00:16，Lai Jiangshan <jiangshanlai@gmail.com> wrote：
> 
> On Sun, Mar 31, 2024 at 7:10 PM Joel Fernandes <joel@joelfernandes.org> wrote:
>> 
>> 
>> 
>>> On Mar 28, 2024, at 1:20 PM, Lai Jiangshan <jiangshanlai@gmail.com> wrote:
>>> 
>>> From: Lai Jiangshan <jiangshan.ljs@antgroup.com>
>>> 
>>> Prepare for arch-specific-defined rcu_preempt_depth_set().
>>> 
>>> No functionality change intended, but it has to be defined as a macro
>>> as rcupdate.h is a very low level header included from areas that don't
>>> even know about the task struct "current".
>> 
>> Sorry I did not follow changelog. If some rcupdate.h includers do not know
>> about task_struct, how does adding a macro that uses current help?
>> 
> 
> Hello
> 
> This is how macro works and it expands blindly based on tokens on the
> usage-sites.

But ‘current’ still needs to be expanded at last, it seems to me that it only affects 
the including order of the header files？

Or what am I missing?

> 
> And rcu_preempt_depth() & rcu_preempt_depth_set() are not universally
> used wrappers, the user can simply also include linux/sched.h to make
> they work.
> 
> Thanks
> Lai
> 

2024年4月1日 19:40，Alan Huang <mmpgouride@gmail.com> wrote：
> 
> 2024年4月1日 00:16，Lai Jiangshan <jiangshanlai@gmail.com> wrote：
>> 
>> On Sun, Mar 31, 2024 at 7:10 PM Joel Fernandes <joel@joelfernandes.org> wrote:
>>> 
>>> 
>>> 
>>>> On Mar 28, 2024, at 1:20 PM, Lai Jiangshan <jiangshanlai@gmail.com> wrote:
>>>> 
>>>> From: Lai Jiangshan <jiangshan.ljs@antgroup.com>
>>>> 
>>>> Prepare for arch-specific-defined rcu_preempt_depth_set().
>>>> 
>>>> No functionality change intended, but it has to be defined as a macro
>>>> as rcupdate.h is a very low level header included from areas that don't
>>>> even know about the task struct "current".
>>> 
>>> Sorry I did not follow changelog. If some rcupdate.h includers do not know
>>> about task_struct, how does adding a macro that uses current help?
>>> 
>> 
>> Hello
>> 
>> This is how macro works and it expands blindly based on tokens on the
>> usage-sites.
> 
> But ‘current’ still needs to be expanded at last, it seems to me that it only affects 
> the including order of the header files？
> 
> Or what am I missing?

Get the missing part: if the user don’t need to use rcu_preempt_depth() 
and rcu_preempt_depth_set() but other parts of rcupdate.h, then the two
has to be defined as a macro to avoid including linux/sched.h.

Sorry for the bother.

> 
>> 
>> And rcu_preempt_depth() & rcu_preempt_depth_set() are not universally
>> used wrappers, the user can simply also include linux/sched.h to make
>> they work.
>> 
>> Thanks
>> Lai

> On Mar 31, 2024, at 9:46 PM, Lai Jiangshan <jiangshanlai@gmail.com> wrote:
> 
> On Sun, Mar 31, 2024 at 7:10 PM Joel Fernandes <joel@joelfernandes.org> wrote:
>> 
>> 
>> 
>>>> On Mar 28, 2024, at 1:20 PM, Lai Jiangshan <jiangshanlai@gmail.com> wrote:
>>> 
>>> From: Lai Jiangshan <jiangshan.ljs@antgroup.com>
>>> 
>>> Prepare for arch-specific-defined rcu_preempt_depth_set().
>>> 
>>> No functionality change intended, but it has to be defined as a macro
>>> as rcupdate.h is a very low level header included from areas that don't
>>> even know about the task struct "current".
>> 
>> Sorry I did not follow changelog. If some rcupdate.h includers do not know
>> about task_struct, how does adding a macro that uses current help?
>> 
> 
> Hello
> 
> This is how macro works and it expands blindly based on tokens on the
> usage-sites.
> 
> And rcu_preempt_depth() & rcu_preempt_depth_set() are not universally
> used wrappers, the user can simply also include linux/sched.h to make
> they work.

Oh I see, so by hiding it in a macro, the code remains unexpanded. That makes sense..

Thanks.





> 
> Thanks
> Lai