From: Mikulas Patocka <mpatocka@redhat.com>
Date: Thu, 30 Oct 2008 13:33:12 +0000 (+0000)
Subject: dm snapshot: fix register_snapshot deadlock
X-Git-Tag: v2.6.28-rc3~40^2~1
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=60c856c8e2f57a3f69c505735ef66e3719ea0bd6;p=pandora-kernel.git

dm snapshot: fix register_snapshot deadlock

register_snapshot() performs a GFP_KERNEL allocation while holding
_origins_lock for write, but that could write out dirty pages onto a
device that attempts to acquire _origins_lock for read, resulting in
deadlock.

So move the allocation up before taking the lock.

This path is not performance-critical, so it doesn't matter that we
allocate memory and free it if we find that we won't need it.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
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