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Date:   Wed, 1 Apr 2020 15:42:34 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Michel Lespinasse <walken@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        linux-mm <linux-mm@kvack.org>,
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        Markus Elfring <Markus.Elfring@web.de>
Subject: Re: [PATCH v3 06/10] mmap locking API: convert nested write lock
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On Fri, Mar 27, 2020 at 03:50:58PM -0700, Michel Lespinasse wrote:

> @@ -26,6 +31,12 @@ static inline void mmap_write_unlock(struct mm_struct *mm)
>  	up_write(&mm->mmap_sem);
>  }
>  
> +/* Pairs with mmap_write_lock_nested() */
> +static inline void mmap_write_unlock_nested(struct mm_struct *mm)
> +{
> +	up_write(&mm->mmap_sem);
> +}
> +
>  static inline void mmap_downgrade_write_lock(struct mm_struct *mm)
>  {
>  	downgrade_write(&mm->mmap_sem);

Why does unlock_nested() make sense ?