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Message-ID: <cf20bbbc-c435-326d-f31a-86b1f4ce927a@redhat.com>
Date:   Fri, 26 May 2023 14:49:33 -0400
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Subject: Re: [RFC][PATCH 1/2] locking: Introduce __cleanup__ based guards
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To:     Peter Zijlstra <peterz@infradead.org>,
        torvalds@linux-foundation.org, keescook@chromium.org,
        gregkh@linuxfoundation.org, pbonzini@redhat.com
Cc:     linux-kernel@vger.kernel.org, ojeda@kernel.org,
        ndesaulniers@google.com, mingo@redhat.com, will@kernel.org,
        boqun.feng@gmail.com, juri.lelli@redhat.com,
        vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
        rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
        bristot@redhat.com, vschneid@redhat.com, paulmck@kernel.org,
        frederic@kernel.org, quic_neeraju@quicinc.com,
        joel@joelfernandes.org, josh@joshtriplett.org,
        mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com,
        qiang1.zhang@intel.com, rcu@vger.kernel.org, tj@kernel.org,
        tglx@linutronix.de
References: <20230526150549.250372621@infradead.org>
 <20230526151946.960406324@infradead.org>
From:   Waiman Long <longman@redhat.com>
In-Reply-To: <20230526151946.960406324@infradead.org>
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On 5/26/23 11:05, Peter Zijlstra wrote:
> Use __attribute__((__cleanup__(func))) to buid various guards:
>
>   - ptr_guard()
>   - void_guard() / void_scope()
>   - lock_guard() / lock_scope()
>   - double_lock_guard() / double_lock_scope()
>
> Where the _guard thingies are variables with scope-based cleanup and
> the _scope thingies are basically do-once for-loops with the same.
>
> The CPP is rather impenetrable -- but I'll attempt to write proper
> comments if/when people think this is worth pursuing.
>
> Actual usage in the next patch
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>   include/linux/compiler_attributes.h |    2
>   include/linux/irqflags.h            |    7 ++
>   include/linux/guards.h          |  118 ++++++++++++++++++++++++++++++++++++
>   include/linux/mutex.h               |    5 +
>   include/linux/preempt.h             |    4 +
>   include/linux/rcupdate.h            |    3
>   include/linux/sched/task.h          |    2
>   include/linux/spinlock.h            |   23 +++++++
>   8 files changed, 164 insertions(+)

That is an interesting idea and may help to simplify some of the common 
code patterns that we have in the kernel. The macros are a bit hard to 
read and understand though I thought I got a rough idea of what they are 
trying to do.

BTW, do we have a use case for double_lock_guard/double_lock_scope? I 
can envision a nested lock_scope inside a lock_scope, but taking 2 auto 
locks of the same type at init time and then unlock them at exit just 
doesn't make sense to me.

Cheers,
Longman