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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: c62c38f6b9 ("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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.