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>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/ocfs2/namei.c b/fs/ocfs2/namei.c
index 55c9d90caaaf..4d1ea8703fcd 100644
--- a/fs/ocfs2/namei.c
+++ b/fs/ocfs2/namei.c
@@ -566,7 +566,7 @@ static int __ocfs2_mknod_locked(struct inode *dir,
 	fe->i_last_eb_blk = 0;
 	strcpy(fe->i_signature, OCFS2_INODE_SIGNATURE);
 	fe->i_flags |= cpu_to_le32(OCFS2_VALID_FL);
-	ktime_get_real_ts64(&ts);
+	ktime_get_coarse_real_ts64(&ts);
 	fe->i_atime = fe->i_ctime = fe->i_mtime =
 		cpu_to_le64(ts.tv_sec);
 	fe->i_mtime_nsec = fe->i_ctime_nsec = fe->i_atime_nsec =