From: Josef Bacik <josef@redhat.com>
Date: Sun, 24 Jul 2011 19:45:34 +0000 (-0400)
Subject: Btrfs: fix deadlock when throttling transactions
X-Git-Tag: v3.1-rc1~134^2^2~6
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=81317fdeddcef259b6ecf7b5c0d04caa167c6b54;p=pandora-kernel.git

Btrfs: fix deadlock when throttling transactions

Hit this nice little deadlock.  What happens is this

__btrfs_end_transaction with throttle set, --use_count so it equals 0
  btrfs_commit_transaction
    <somebody else actually manages to start the commit>
    btrfs_end_transaction --use_count so now its -1 <== BAD
      we just return and wait on the transaction

This is bad because we just return after our use_count is -1 and don't let go
of our num_writer count on the transaction, so the guy committing the
transaction just sits there forever.  Fix this by inc'ing our use_count if we're
going to call commit_transaction so that if we call btrfs_end_transaction it's
valid.  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
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