[PATCH] fs: compare truncated timestamps in current_mgtime

[PATCH] fs: compare truncated timestamps in current_mgtime

[Jeff Layton]

current_mgtime compares the ctime (which has already been truncated) to
the value from ktime_get_coarse_real_ts64 (which has not). All of the
existing filesystems that enable mgtime have 1ns granularity, so this is
not a problem today, but it is more correct to compare truncated
timestamps instead.

Do the truncate earlier, so we're comparing like things.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/inode.c | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index 369621e7faf5..8199d0e02cce 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -2097,28 +2097,28 @@ EXPORT_SYMBOL(file_remove_privs);
  */
 static struct timespec64 current_mgtime(struct inode *inode)
 {
-	struct timespec64 now;
+	struct timespec64 now, ctime;
 	atomic_long_t *pnsec = (atomic_long_t *)&inode->__i_ctime.tv_nsec;
 	long nsec = atomic_long_read(pnsec);
 
 	if (nsec & I_CTIME_QUERIED) {
 		ktime_get_real_ts64(&now);
-	} else {
-		struct timespec64 ctime;
+		return timestamp_truncate(now, inode);
+	}
 
-		ktime_get_coarse_real_ts64(&now);
+	ktime_get_coarse_real_ts64(&now);
+	now = timestamp_truncate(now, inode);
 
-		/*
-		 * If we've recently fetched a fine-grained timestamp
-		 * then the coarse-grained one may still be earlier than the
-		 * existing one. Just keep the existing ctime if so.
-		 */
-		ctime = inode_get_ctime(inode);
-		if (timespec64_compare(&ctime, &now) > 0)
-			now = ctime;
-	}
+	/*
+	 * If we've recently fetched a fine-grained timestamp
+	 * then the coarse-grained one may still be earlier than the
+	 * existing ctime. Just keep the existing value if so.
+	 */
+	ctime = inode_get_ctime(inode);
+	if (timespec64_compare(&ctime, &now) > 0)
+		now = ctime;
 
-	return timestamp_truncate(now, inode);
+	return now;
 }
 
 /**

---
base-commit: 4ce0966ed7c04881c5f352e0bb53af9b38f94253
change-id: 20230728-mgctime-5e0ec0e89b04

Best regards,
-- 
Jeff Layton <jlayton@kernel.org>

Re: [PATCH] fs: compare truncated timestamps in current_mgtime

[Christian Brauner]

On Fri, 28 Jul 2023 09:21:37 -0400, Jeff Layton wrote:
> current_mgtime compares the ctime (which has already been truncated) to
> the value from ktime_get_coarse_real_ts64 (which has not). All of the
> existing filesystems that enable mgtime have 1ns granularity, so this is
> not a problem today, but it is more correct to compare truncated
> timestamps instead.
> 
> Do the truncate earlier, so we're comparing like things.
> 
> [...]

Applied to the vfs.ctime branch of the vfs/vfs.git tree.
Patches in the vfs.ctime branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs.ctime

[1/1] fs: compare truncated timestamps in current_mgtime
      https://git.kernel.org/vfs/vfs/c/dec705a2d44a