[Natty][SRU] Fix for bug 857170

[Herton R. Krzesinski]

From: Herton Ronaldo Krzesinski <herton.krzesinski at canonical.com>

Bug 857170 - "Kernel oops when mounting UDF volume"

SRU Justification

Impact

Regression after the update to 2.6.38.8, there is a possibility of crash
in block code after the change "block: don't block events on excl write
for non-optical devices", like the one reported in bug 857170

Fix

Fixed by upstream commit 4c49ff3fe128ca68dabd07537415c419ad7f82f9,
tested by the reporter.

Testcase

Report in bug 857170 shows one way to reproduce the issue.

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Herton