[REGRESSION] loop: use vfs_getattr_nosec for accurate file size

["Theodore Ts'o" <tytso@mit.edu>]

Hi, I was testing 6.17-rc3, and I noticed a test failure in fstest
generic/563[1], when testing both ext4 and xfs.  If you are using my
test appliance[2], this can be trivially reproduced using:

   kvm-xfstests -c ext4/4k generic/563
or
   kvm-xfstests -c xfs/4k generic/563

[1] https://git.kernel.org/pub/scm/fs/xfs/xfstests-dev.git/tree/tests/generic/563
[2] https://github.com/tytso/xfstests-bld/blob/master/Documentation/kvm-quickstart.md

A git bisect pointed the problem at:

commit 47b71abd58461a67cae71d2f2a9d44379e4e2fcf
Author: Rajeev Mishra <rajeevm@hpe.com>
Date:   Mon Aug 18 18:48:21 2025 +0000

    loop: use vfs_getattr_nosec for accurate file size
    
    Use vfs_getattr_nosec() in lo_calculate_size() for getting the file
    size, rather than just read the cached inode size via i_size_read().
    This provides better results than cached inode data, particularly for
    network filesystems where metadata may be stale.
    
    Signed-off-by: Rajeev Mishra <rajeevm@hpe.com>
    Reviewed-by: Yu Kuai <yukuai3@huawei.com>
    Link: https://lore.kernel.org/r/20250818184821.115033-3-rajeevm@hpe.com
    [axboe: massage commit message]
    Signed-off-by: Jens Axboe <axboe@kernel.dk>

... and indeed if I go to 6.17-rc3, and revert this commit,
generic/563 starts passing again.

Could you please take a look, and/or revert this change?  Many thanks!

      	  	      	      	 	- Ted