linux-kernel - Re: [PATCH RFC] lib: Make radix_tree_node

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Message-ID: <20130717201453.GH22392@kernel.dk>
Date:	Wed, 17 Jul 2013 14:14:53 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Jan Kara <jack@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [PATCH RFC] lib: Make radix_tree_node_alloc() irq safe

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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