linux-kernel - Re: [PATCH 11/33] cpuset: Provide lockdep check for cpuset lock held

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Message-ID: <b94f6159-a280-4890-a02a-f19ff808de5b@huaweicloud.com>
Date: Tue, 14 Oct 2025 21:29:25 +0800
From: Chen Ridong <chenridong@...weicloud.com>
To: Frederic Weisbecker <frederic@...nel.org>,
 LKML <linux-kernel@...r.kernel.org>
Cc: Michal Koutný <mkoutny@...e.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Bjorn Helgaas <bhelgaas@...gle.com>,
 Catalin Marinas <catalin.marinas@....com>, Danilo Krummrich
 <dakr@...nel.org>, "David S . Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Gabriele Monaco <gmonaco@...hat.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Ingo Molnar <mingo@...hat.com>, Jakub Kicinski <kuba@...nel.org>,
 Jens Axboe <axboe@...nel.dk>, Johannes Weiner <hannes@...xchg.org>,
 Lai Jiangshan <jiangshanlai@...il.com>,
 Marco Crivellari <marco.crivellari@...e.com>, Michal Hocko
 <mhocko@...e.com>, Muchun Song <muchun.song@...ux.dev>,
 Paolo Abeni <pabeni@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
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 Tejun Heo <tj@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
 Vlastimil Babka <vbabka@...e.cz>, Waiman Long <longman@...hat.com>,
 Will Deacon <will@...nel.org>, cgroups@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-block@...r.kernel.org,
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Subject: Re: [PATCH 11/33] cpuset: Provide lockdep check for cpuset lock held

On 2025/10/14 4:31, Frederic Weisbecker wrote:
> cpuset modifies partitions, including isolated, while holding the cpuset
> mutex.
> 
> This means that holding the cpuset mutex is safe to synchronize against
> housekeeping cpumask changes.
> 
> Provide a lockdep check to validate that.
> 
> Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
> ---
>  include/linux/cpuset.h | 2 ++
>  kernel/cgroup/cpuset.c | 7 +++++++
>  2 files changed, 9 insertions(+)
> 
> diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
> index 2ddb256187b5..051d36fec578 100644
> --- a/include/linux/cpuset.h
> +++ b/include/linux/cpuset.h
> @@ -18,6 +18,8 @@
>  #include <linux/mmu_context.h>
>  #include <linux/jump_label.h>
>  
> +extern bool lockdep_is_cpuset_held(void);
> +
>  #ifdef CONFIG_CPUSETS
>  
>  /*
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 8595f1eadf23..aa1ac7bcf2ea 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -279,6 +279,13 @@ void cpuset_full_unlock(void)
>  	cpus_read_unlock();
>  }
>  
> +#ifdef CONFIG_LOCKDEP
> +bool lockdep_is_cpuset_held(void)
> +{
> +	return lockdep_is_held(&cpuset_mutex);
> +}
> +#endif
> +
>  static DEFINE_SPINLOCK(callback_lock);
>  
>  void cpuset_callback_lock_irq(void)

Is the lockdep_is_cpuset_held function actually being used?
If CONFIG_LOCKDEP is disabled, compilation would fail with an "undefined reference to
lockdep_is_cpuset_held" error.

-- 
Best regards,
Ridong