linux-kernel - Re: [PATCH v4 09/10] mmap locking API: use lockdep_assert

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Date:   Mon, 20 Apr 2020 19:35:42 -0700
From:   Matthew Wilcox <willy@...radead.org>
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>,
        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>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Daniel Jordan <daniel.m.jordan@...cle.com>
Subject: Re: [PATCH v4 09/10] mmap locking API: use lockdep_assert_held

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);
}