4.19-stable review patch. If anyone has any objections, please let me know.
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From: Su Yue glass.su@suse.com
commit b8cb324277ee16f3eca3055b96fce4735a5a41c6 upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/ocfs2/namei.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/fs/ocfs2/namei.c +++ b/fs/ocfs2/namei.c @@ -571,7 +571,7 @@ 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 =