linux-kernel - Re: [PATCH] radix_tree_tag_get() is not as safe as the docs make out

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Message-ID: <alpine.LFD.2.00.1004061236290.3487@i5.linux-foundation.org>
Date:	Tue, 6 Apr 2010 12:39:17 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	David Howells <dhowells@...hat.com>
cc:	akpm@...ux-foundation.org, npiggin@...e.de,
	paulmck@...ux.vnet.ibm.com, corbet@....net,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] radix_tree_tag_get() is not as safe as the docs make
 out



On Tue, 6 Apr 2010, David Howells wrote:
>
> radix_tree_tag_get() is not safe to use concurrently with radix_tree_tag_set()
> or radix_tree_tag_clear().  The problem is that the double tag_get() in
> radix_tree_tag_get():
 [ snip snip ]

Looks like a reasonable patch, but the one thing you didn't say is whether 
there is any code that relies on the incorrectly documented behavior?

How did you find this? Do we need to fix actual code too? The only user 
seems to be your fscache/page.c thing, and I'm not seeing any locking 
except for the rcu locking that is apparently not sufficient.

			Linus
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