linux-kernel - Re: [PATCH 02/10] rcu: Move rcu_preempt_depth

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Message-Id: <60BB1971-38D3-4FE2-BB45-2DE228C6F370@gmail.com>
Date: Mon, 1 Apr 2024 19:57:40 +0800
From: Alan Huang <mmpgouride@...il.com>
To: Lai Jiangshan <jiangshanlai@...il.com>
Cc: Joel Fernandes <joel@...lfernandes.org>,
 linux-kernel@...r.kernel.org,
 rcu@...r.kernel.org,
 x86@...nel.org,
 Lai Jiangshan <jiangshan.ljs@...group.com>,
 "Paul E. McKenney" <paulmck@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>,
 Frederic Weisbecker <frederic@...nel.org>,
 Neeraj Upadhyay <quic_neeraju@...cinc.com>,
 Josh Triplett <josh@...htriplett.org>,
 Boqun Feng <boqun.feng@...il.com>,
 Steven Rostedt <rostedt@...dmis.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Zqiang <qiang.zhang1211@...il.com>
Subject: Re: [PATCH 02/10] rcu: Move rcu_preempt_depth_set() to rcupdate.h

2024年4月1日 19:40，Alan Huang <mmpgouride@...il.com> wrote：
> 
> 2024年4月1日 00:16，Lai Jiangshan <jiangshanlai@...il.com> wrote：
>> 
>> On Sun, Mar 31, 2024 at 7:10 PM Joel Fernandes <joel@...lfernandes.org> wrote:
>>> 
>>> 
>>> 
>>>> On Mar 28, 2024, at 1:20 PM, Lai Jiangshan <jiangshanlai@...il.com> wrote:
>>>> 
>>>> From: Lai Jiangshan <jiangshan.ljs@...group.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