linux-kernel - Re: [PATCH] radix tree: Don't return internal entries on lookup

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Message-ID: <20181206133620.GC24603@bombadil.infradead.org>
Date:   Thu, 6 Dec 2018 05:36:20 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Greg Kurz <groug@...d.org>
Cc:     linux-kernel@...r.kernel.org, Josef Bacik <jbacik@...com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Frederic Barrat <fbarrat@...ux.vnet.ibm.com>
Subject: Re: [PATCH] radix tree: Don't return internal entries on lookup

On Thu, Dec 06, 2018 at 08:54:03AM +0100, Greg Kurz wrote:
> Commit 66ee620f06f9 ("idr: Permit any valid kernel pointer to
> be stored") changed the radix tree lookup so that it stops when
> reaching the bottom of the tree. But radix_tree_descend() may have
> changed the node variable to point to an internal entry which then
> gets returned to the caller and bad things may happen.

> pe_data is equal to R3 which is the return value of radix_tree_lookup(),
> ie, 0x406 == RADIX_TREE_RETRY.

Thank you for the report and the debugging!  I've decided to fix the
problem slightly differently, and I've also added a test to the test-suite
that reproduces the problem in only a few iterations (the largest I've
seen is a few hundred; and often it'll reproduce in under twenty).

You can see it here:
http://git.infradead.org/users/willy/linux-dax.git/commitdiff/eff3860bbfedbac6edac57fb0d7f3a60e860c1c3

I'll give the build bots a couple of days to chew on it and then ask
Linus to pull it.