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Date:   Mon, 20 Apr 2020 19:35:42 -0700
From:   Matthew Wilcox <willy@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>,
        Peter Zijlstra <peterz@infradead.org>,
        Laurent Dufour <ldufour@linux.ibm.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        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>,
        Daniel Jordan <daniel.m.jordan@oracle.com>
Subject: Re: [PATCH v4 09/10] mmap locking API: use lockdep_assert_held
Message-ID: <20200421023542.GJ5820@bombadil.infradead.org>
References: <20200415004353.130248-1-walken@google.com>
 <20200415004353.130248-10-walken@google.com>
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On Tue, Apr 14, 2020 at 05:43:52PM -0700, Michel Lespinasse wrote:
> Use lockdep_assert_held when asserting that mmap_sem is held.
> 
> Using this instead of rwsem_is_locked makes the assertions more
> tolerant of future changes to the lock type.

Somebody pointed out on an earlier iteration of this patch set that
rwsem_is_locked() is enabled on all rwsems whereas lockdep_assert_held()
is only enabled when lockdep is enabled, which is not production setups.

How about this?

static inline void mm_assert_locked(struct mm_struct *mm)
{
	if (IS_ENABLED(CONFIG_LOCKDEP) && debug_locks)
		VM_BUG_ON_MM(!lockdep_is_held(&mm->mmap_sem), mm);
	else
		VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm);
}