linux-kernel - Re: [RFC v2 01/10] mm: Deactivate mmap

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Date:   Wed, 31 May 2017 08:40:10 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     Laurent Dufour <ldufour@...ux.vnet.ibm.com>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        Jan Kara <jack@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Michal Hocko <mhocko@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Andi Kleen <andi@...stfloor.org>, haren@...ux.vnet.ibm.com,
        aneesh.kumar@...ux.vnet.ibm.com, khandual@...ux.vnet.ibm.com,
        paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC v2 01/10] mm: Deactivate mmap_sem assert

Hi Laurent!

On Wed, 24 May 2017, Laurent Dufour wrote:

>When mmap_sem will be moved to a range lock, some assertion done in
>the code will have to be reviewed to work with the range locking as
>well.
>
>This patch disables these assertions for the moment but it has be
>reviewed later once the range locking API will provide the dedicated
>services.

Lets not do this; we should _at least_ provide the current checks
we already have. The following should be a (slower) equivalent once
we have the interval_tree_iter_first() optimization sorted out.

int range_is_locked(struct range_lock_tree *tree, struct range_lock *lock)
{
	unsigned long flags;
	struct interval_tree_node *node;

	spin_lock_irqsave(&tree->lock, flags);
	node = interval_tree_iter_first(&tree->root, lock->node.start,
					lock->node.last);
	spin_unlock_irqrestore(&tree->lock, flags);

	return node != NULL;
}
EXPORT_SYMBOL_GPL(range_is_locked);

Thanks,
Davidlohr