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Date: Wed, 17 Jul 2013 14:14:53 -0600
From: Jens Axboe <axboe@kernel.dk>
To: Jan Kara <jack@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>, linux-mm@kvack.org
Subject: Re: [PATCH RFC] lib: Make radix_tree_node_alloc() irq safe
Message-ID: <20130717201453.GH22392@kernel.dk>
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On Tue, Jul 16 2013, Jan Kara wrote:
> With users of radix_tree_preload() run from interrupt (CFQ is one such
> possible user), the following race can happen:
> 
> radix_tree_preload()
> ...
> radix_tree_insert()
>   radix_tree_node_alloc()
>     if (rtp->nr) {
>       ret = rtp->nodes[rtp->nr - 1];
> <interrupt>
> ...
> radix_tree_preload()
> ...
> radix_tree_insert()
>   radix_tree_node_alloc()
>     if (rtp->nr) {
>       ret = rtp->nodes[rtp->nr - 1];
> 
> And we give out one radix tree node twice. That clearly results in radix
> tree corruption with different results (usually OOPS) depending on which
> two users of radix tree race.
> 
> Fix the problem by disabling interrupts when working with rtp variable.
> In-interrupt user can still deplete our preloaded nodes but at least we
> won't corrupt radix trees.

Looks good to me, great catch Jan.

-- 
Jens Axboe

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