ext4: Use bitops to read/modify i_flags in struct ext4_inode_info

ext4: Use bitops to read/modify i_flags in struct ext4_inode_info

commit 12e9b892002d9af057655d35b44db8ee9243b0dc upstream.

At several places we modify EXT4_I(inode)->i_flags without holding
i_mutex (ext4_do_update_inode, ...). These modifications are racy and
we can lose updates to i_flags. So convert handling of i_flags to use
bitops which are atomic.

https://bugzilla.kernel.org/show_bug.cgi?id=15792

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>