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Date:   Thu, 26 Mar 2020 21:46:47 -0700
From:   Davidlohr Bueso <dave@stgolabs.net>
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>,
        Peter Zijlstra <peterz@infradead.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>,
        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 v2 07/10] mmap locking API: add mmap_read_release() and
 mmap_read_unlock_non_owner()
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        Liam Howlett <Liam.Howlett@oracle.com>,
        Jerome Glisse <jglisse@redhat.com>,
        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>
References: <20200327021058.221911-1-walken@google.com>
 <20200327021058.221911-8-walken@google.com>
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On Thu, 26 Mar 2020, 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.

I'm not crazy about the idea generalizing such calls into an mm api.
We try to stay away from non-owner semantics in locking - granted
the IS_ENABLED(CONFIG_PREEMPT_RT) warning, but still.

Could this give future users the wrong impression? What about just
using rwsem calls directly in bpf?

Thanks,
Davidlohr