ocfs2: use coarse time for new created files

The default atime related mount option is '-o realtime' which means file
atime should be updated if atime <= ctime or atime <= mtime.  atime should
be updated in the following scenario, but it is not:
==========================================================
$ rm /mnt/testfile;
$ echo test > /mnt/testfile
$ stat -c "%X %Y %Z" /mnt/testfile
1711881646 1711881646 1711881646
$ sleep 5
$ cat /mnt/testfile > /dev/null
$ stat -c "%X %Y %Z" /mnt/testfile
1711881646 1711881646 1711881646
==========================================================

And the reason the atime in the test is not updated is that ocfs2 calls
ktime_get_real_ts64() in __ocfs2_mknod_locked during file creation.  Then
inode_set_ctime_current() is called in inode_set_ctime_current() calls
ktime_get_coarse_real_ts64() to get current time.

ktime_get_real_ts64() is more accurate than ktime_get_coarse_real_ts64(). 
In my test box, I saw ctime set by ktime_get_coarse_real_ts64() is less
than ktime_get_real_ts64() even ctime is set later.  The ctime of the new
inode is smaller than atime.

The call trace is like:

ocfs2_create
  ocfs2_mknod
    __ocfs2_mknod_locked
    ....

      ktime_get_real_ts64 <------- set atime,ctime,mtime, more accurate
      ocfs2_populate_inode
    ...
    ocfs2_init_acl
      ocfs2_acl_set_mode
        inode_set_ctime_current
          current_time
            ktime_get_coarse_real_ts64 <-------less accurate

ocfs2_file_read_iter
  ocfs2_inode_lock_atime
    ocfs2_should_update_atime
      atime <= ctime ? <-------- false, ctime < atime due to accuracy

So here call ktime_get_coarse_real_ts64 to set inode time coarser while
creating new files.  It may lower the accuracy of file times.  But it's
not a big deal since we already use coarse time in other places like
ocfs2_update_inode_atime and inode_set_ctime_current.

Link: https://lkml.kernel.org/r/20240408082041.20925-5-glass.su@suse.com
Fixes: c62c38f6b91b ("ocfs2: replace CURRENT_TIME macro")
Signed-off-by: Su Yue <glass.su@suse.com>
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Gang He <ghe@suse.com>
Cc: Jun Piao <piaojun@huawei.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

0 files changed, 0 insertions, 0 deletions