The patch titled
Subject: ocfs2: use coarse time for new created files
has been added to the -mm mm-nonmm-unstable branch. Its filename is
ocfs2-use-coarse-time-for-new-created-files.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/ocfs2-use-coarse-time-for-new-created-files.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Su Yue <glass.su@xxxxxxxx>
Subject: ocfs2: use coarse time for new created files
Date: Tue, 2 Apr 2024 09:46:51 +0800
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/20240402014651.13723-5-glass.su@xxxxxxxx
Signed-off-by: Su Yue <glass.su@xxxxxxxx>
Reviewed-by: Joseph Qi <joseph.qi@xxxxxxxxxxxxxxxxx>
Cc: Changwei Ge <gechangwei@xxxxxxx>
Cc: Gang He <ghe@xxxxxxxx>
Cc: Joel Becker <jlbec@xxxxxxxxxxxx>
Cc: Jun Piao <piaojun@xxxxxxxxxx>
Cc: Junxiao Bi <junxiao.bi@xxxxxxxxxx>
Cc: Mark Fasheh <mark@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/ocfs2/namei.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/fs/ocfs2/namei.c~ocfs2-use-coarse-time-for-new-created-files
+++ a/fs/ocfs2/namei.c
@@ -566,7 +566,7 @@ static int __ocfs2_mknod_locked(struct i
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 =
_
Patches currently in -mm which might be from glass.su@xxxxxxxx are
ocfs2-update-inode-ctime-in-ocfs2_fileattr_set.patch
ocfs2-return-real-error-code-in-ocfs2_dio_wr_get_block.patch
ocfs2-fix-races-between-hole-punching-and-aiodio.patch
ocfs2-update-inode-fsync-transaction-id-in-ocfs2_unlink-and-ocfs2_link.patch
ocfs2-use-coarse-time-for-new-created-files.patch
