From 01a33b4ace68bc35679a347f21d5ed6e222e30dc Mon Sep 17 00:00:00 2001
From: Matthew Wilcox <willy@linux.intel.com>
Date: Tue, 8 Sep 2015 14:59:22 -0700
Subject: [PATCH] ext4: start transaction before calling into DAX

Jan Kara pointed out that in the case where we are writing to a hole, we
can end up with a lock inversion between the page lock and the journal
lock.  We can avoid this by starting the transaction in ext4 before
calling into DAX.  The journal lock nests inside the superblock
pagefault lock, so we have to duplicate that code from dax_fault, like
XFS does.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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