linux-kernel - Re: [PATCH 1/8] mmap locking API: initial implementation as rwsem wrappers

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Message-ID: <20200326175644.GN20941@ziepe.ca>
Date:   Thu, 26 Mar 2020 14:56:44 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Michel Lespinasse <walken@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Matthew Wilcox <willy@...radead.org>,
        Liam Howlett <Liam.Howlett@...cle.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        David Rientjes <rientjes@...gle.com>,
        Hugh Dickins <hughd@...gle.com>, Ying Han <yinghan@...gle.com>
Subject: Re: [PATCH 1/8] mmap locking API: initial implementation as rwsem
 wrappers

On Thu, Mar 26, 2020 at 12:02:29AM -0700, Michel Lespinasse wrote:

> +static inline bool mmap_is_locked(struct mm_struct *mm)
> +{
> +	return rwsem_is_locked(&mm->mmap_sem) != 0;
> +}

I've been wondering if the various VM_BUG(rwsem_is_locked()) would be
better as lockdep expressions? Certainly when lockdep is enabled it
should be preferred, IMHO.

So, I think if inlines are to be introduced this should be something
similar to netdev's ASSERT_RTNL which seems to have worked well.

Maybe ASSERT_MMAP_SEM_READ/WRITE/HELD() and do the VM_BUG or
lockdep_is_held as appropriate?

Jason