linux-kernel - Re: [PATCH v5 09/10] mmap locking API: add mmap_assert

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Date:   Tue, 21 Apr 2020 19:10:39 -0700
From:   Michel Lespinasse <walken@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>
Cc:     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>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Daniel Jordan <daniel.m.jordan@...cle.com>
Subject: Re: [PATCH v5 09/10] mmap locking API: add mmap_assert_locked

On Tue, Apr 21, 2020 at 5:14 PM Michel Lespinasse <walken@...gle.com> wrote:
> +static inline void mmap_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);
> +}

Turns out this function definition does not work for !CONFIG_LOCKDEP
as lockdep_is_held is not defined in that case.

The following should work instead:

static inline void mmap_assert_locked(struct mm_struct *mm)
{
#ifdef CONFIG_LOCKDEP
        if (debug_locks) {
                VM_BUG_ON_MM(!lockdep_is_held(&mm->mmap_lock), mm);
                return;
        }
#endif
        VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm);
}