[SRU][Yakkety][Xenial][PATCH 0/1] btrfs: Continue write in case of can_not_nocow

[Joseph Salisbury]

BugLink: http://bugs.launchpad.net/bugs/1584052

== SRU Justification ==
The 4.4 kernel introduced a btrfs bug where a process writing a file while a snapshot creation is underway will receive a false ENOSPC error (No space left on device), even while there is plenty of free space on the file system. On systems where snapshots are created frequently, this leads to frequent database crashes, MySQL for this particular bug.

Creating snapshots for undo and backup purposes without interrupting database operations is a central aspect of btrfs usage. This bug breaks server operations, which is why a fix is needed in Xenial.

Commit 4da2e26 is in Mainline as of 4.6-rc2.  This commit will only be needed in Yakkety until it is rebased to upstream 4.6 or newer. 

Upstream discussion about this bug:
The problem is well known: http://www.spinics.net/lists/linux-btrfs/msg52672.html


== Fix ==
commit 4da2e26a2a32b174878744bd0f07db180c875f26
Author: Zhao Lei <zhaolei at cn.fujitsu.com>
Date:   Wed Jan 6 18:24:43 2016 +0800

    btrfs: Continue write in case of can_not_nocow


== Test Case ==
A test kernel was built with this patch and tested by the original bug reporter.
The bug reporter states the test kernel resolved the bug.





Zhao Lei (1):
  btrfs: Continue write in case of can_not_nocow

 fs/btrfs/file.c | 37 +++++++++++++++++--------------------
 1 file changed, 17 insertions(+), 20 deletions(-)

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