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Date:   Wed, 1 Apr 2020 15:46:33 +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>,
        LKML <linux-kernel@vger.kernel.org>,
        Laurent Dufour <ldufour@linux.ibm.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Matthew Wilcox <willy@infradead.org>,
        Liam Howlett <Liam.Howlett@oracle.com>,
        Jerome Glisse <jglisse@redhat.com>,
        Davidlohr Bueso <dave@stgolabs.net>,
        David Rientjes <rientjes@google.com>,
        Hugh Dickins <hughd@google.com>, Ying Han <yinghan@google.com>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Markus Elfring <Markus.Elfring@web.de>
Subject: Re: [PATCH v3 07/10] mmap locking API: add mmap_read_release() and
 mmap_read_unlock_non_owner()
Message-ID: <20200401134633.GS20696@hirez.programming.kicks-ass.net>
References: <20200327225102.25061-1-walken@google.com>
 <20200327225102.25061-8-walken@google.com>
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On Fri, Mar 27, 2020 at 03:50:59PM -0700, Michel Lespinasse wrote:
> Add a couple APIs to allow splitting mmap_read_unlock() into two calls:
> - mmap_read_release(), called by the task that had taken the mmap lock;
> - mmap_read_unlock_non_owner(), called from a work queue.
> 
> These apis are used by kernel/bpf/stackmap.c only.

That code is an absolute abomination and should never have gotten
merged.

That said; I would prefer a mmap_read_trylock_nonowner() over
mmap_read_release() existing.

> Signed-off-by: Michel Lespinasse <walken@google.com>
> ---
>  include/linux/mmap_lock.h | 10 ++++++++++
>  kernel/bpf/stackmap.c     |  9 ++++-----
>  2 files changed, 14 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
> index 36fb758401d6..a80cf9695514 100644
> --- a/include/linux/mmap_lock.h
> +++ b/include/linux/mmap_lock.h
> @@ -62,4 +62,14 @@ static inline void mmap_read_unlock(struct mm_struct *mm)
>  	up_read(&mm->mmap_sem);
>  }
>  
> +static inline void mmap_read_release(struct mm_struct *mm, unsigned long ip)
> +{
> +	rwsem_release(&mm->mmap_sem.dep_map, ip);
> +}
> +
> +static inline void mmap_read_unlock_non_owner(struct mm_struct *mm)
> +{
> +	up_read_non_owner(&mm->mmap_sem);
> +}
> +
>  #endif /* _LINUX_MMAP_LOCK_H */