linux-kernel - dm-crypt: disabling barriers, data corruption

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Message-ID: <feeb478c0705161103idf7b577t4e6011ec506f1747@mail.gmail.com>
Date:	Wed, 16 May 2007 13:03:45 -0500
From:	"Alan Miller" <pushingthecharacterlimit@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: dm-crypt: disabling barriers, data corruption

Prior to 2.6.19, dm-crypt passes write barrier requests through to the
underlying device in the order received unmodified (the ordering).

In 2.6.19 and newer, these writes are now passed through a workqueue.
On an SMP box running encrpytion for write requests in parallel,
wouldn't this cause the requests to arrive to the device in a
different order?  A 2.6.22 patch from Milan Broz sets dm-crypt to
disable barriers, but if this disabling is being handled at the
filesystem level, is there still a chance of data becoming corrupt?

I'm currently running an unpatched 2.6.20 kernel on an SMP machine
testing the validity of some static files going back and forth through
dm-crypt on an XFS filesystem mounted with nobarrier to be sure, and
so far I'm not noticing anything, but this is hardly a good test.
Suggestions or any other way to help out appreciated.
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