linux-kernel - Re: [PATCH 5/5] aio: Refactor aio_read

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 9 Oct 2012 11:37:53 -0700
From:	Zach Brown <zab@...hat.com>
To:	Kent Overstreet <koverstreet@...gle.com>
Cc:	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, tytso@....edu
Subject: Re: [PATCH 5/5] aio: Refactor aio_read_evt, use cmxchg(), fix bug

On Mon, Oct 08, 2012 at 11:39:20PM -0700, Kent Overstreet wrote:
> Bunch of cleanup

Ugh.  That's way too much noisy change for one patch with no
description.  Break it up into functional pieces and actually describe
them.

> events off the ringbuffer without racing with io_getevents().

Are you sure this is safe in the presence of wrapping indices?  It's
been a very long time since I've looked at this, but I could never
convince myself that it was safe.

What I'm worried about is cmpxchg()s caller sampling, say, and index of
0, having another task GO NUTS and wrap that index all the way around
back to 0, and then having that initial cmpchg() caller see the wrapped
0 index and think that's nothing's changed in the interim.

Is this a problem?

(I wish I could find the comment I wrote in a very old patch to tear out
the mapped ring entirely.. It was a great list of its design mistakes.)

- z
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/