diff mbox series

[v6,4/9] fs: have setattr_copy handle multigrain timestamps appropriately

Message ID 20240715-mgtime-v6-4-48e5d34bd2ba@kernel.org
State Not Applicable
Headers show
Series fs: multigrain timestamp redux | expand

Commit Message

Jeff Layton July 15, 2024, 12:48 p.m. UTC 
The setattr codepath is still using coarse-grained timestamps, even on
multigrain filesystems. To fix this, we need to fetch the timestamp for
ctime updates later, at the point where the assignment occurs in
setattr_copy.

On a multigrain inode, ignore the ia_ctime in the attrs, and always
update the ctime to the current clock value. Update the atime and mtime
with the same value (if needed) unless they are being set to other
specific values, a'la utimes().

Note that we don't want to do this universally however, as some
filesystems (e.g. most networked fs) want to do an explicit update
elsewhere before updating the local inode.

Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/attr.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 46 insertions(+), 6 deletions(-)

Comments

Jan Kara July 17, 2024, 11:24 a.m. UTC | #1 
On Mon 15-07-24 08:48:55, Jeff Layton wrote:
> The setattr codepath is still using coarse-grained timestamps, even on
> multigrain filesystems. To fix this, we need to fetch the timestamp for
> ctime updates later, at the point where the assignment occurs in
> setattr_copy.
> 
> On a multigrain inode, ignore the ia_ctime in the attrs, and always
> update the ctime to the current clock value. Update the atime and mtime
> with the same value (if needed) unless they are being set to other
> specific values, a'la utimes().
> 
> Note that we don't want to do this universally however, as some
> filesystems (e.g. most networked fs) want to do an explicit update
> elsewhere before updating the local inode.
> 
> Reviewed-by: Darrick J. Wong <djwong@kernel.org>
> Reviewed-by: Josef Bacik <josef@toxicpanda.com>
> Signed-off-by: Jeff Layton <jlayton@kernel.org>

Looks good to me so feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

What is a bit bothering me is that it's now confusing that ATTR_MTIME_SET /
ATTR_ATIME_SET is handled in different place for mgtime and normal inodes
and I'm concerned this will bite us in the future. But not everybody is
using setattr_copy() and unifying the handling of timestamps seems like
quite some work...

								Honza
diff mbox series

Patch

diff --git a/fs/attr.c b/fs/attr.c
index 825007d5cda4..e03ea6951864 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -271,6 +271,42 @@  int inode_newsize_ok(const struct inode *inode, loff_t offset)
 }
 EXPORT_SYMBOL(inode_newsize_ok);
 
+/**
+ * setattr_copy_mgtime - update timestamps for mgtime inodes
+ * @inode: inode timestamps to be updated
+ * @attr: attrs for the update
+ *
+ * With multigrain timestamps, we need to take more care to prevent races
+ * when updating the ctime. Always update the ctime to the very latest
+ * using the standard mechanism, and use that to populate the atime and
+ * mtime appropriately (unless we're setting those to specific values).
+ */
+static void setattr_copy_mgtime(struct inode *inode, const struct iattr *attr)
+{
+	unsigned int ia_valid = attr->ia_valid;
+	struct timespec64 now;
+
+	/*
+	 * If the ctime isn't being updated then nothing else should be
+	 * either.
+	 */
+	if (!(ia_valid & ATTR_CTIME)) {
+		WARN_ON_ONCE(ia_valid & (ATTR_ATIME|ATTR_MTIME));
+		return;
+	}
+
+	now = inode_set_ctime_current(inode);
+	if (ia_valid & ATTR_ATIME_SET)
+		inode_set_atime_to_ts(inode, attr->ia_atime);
+	else if (ia_valid & ATTR_ATIME)
+		inode_set_atime_to_ts(inode, now);
+
+	if (ia_valid & ATTR_MTIME_SET)
+		inode_set_mtime_to_ts(inode, attr->ia_mtime);
+	else if (ia_valid & ATTR_MTIME)
+		inode_set_mtime_to_ts(inode, now);
+}
+
 /**
  * setattr_copy - copy simple metadata updates into the generic inode
  * @idmap:	idmap of the mount the inode was found from
@@ -303,12 +339,6 @@  void setattr_copy(struct mnt_idmap *idmap, struct inode *inode,
 
 	i_uid_update(idmap, attr, inode);
 	i_gid_update(idmap, attr, inode);
-	if (ia_valid & ATTR_ATIME)
-		inode_set_atime_to_ts(inode, attr->ia_atime);
-	if (ia_valid & ATTR_MTIME)
-		inode_set_mtime_to_ts(inode, attr->ia_mtime);
-	if (ia_valid & ATTR_CTIME)
-		inode_set_ctime_to_ts(inode, attr->ia_ctime);
 	if (ia_valid & ATTR_MODE) {
 		umode_t mode = attr->ia_mode;
 		if (!in_group_or_capable(idmap, inode,
@@ -316,6 +346,16 @@  void setattr_copy(struct mnt_idmap *idmap, struct inode *inode,
 			mode &= ~S_ISGID;
 		inode->i_mode = mode;
 	}
+
+	if (is_mgtime(inode))
+		return setattr_copy_mgtime(inode, attr);
+
+	if (ia_valid & ATTR_ATIME)
+		inode_set_atime_to_ts(inode, attr->ia_atime);
+	if (ia_valid & ATTR_MTIME)
+		inode_set_mtime_to_ts(inode, attr->ia_mtime);
+	if (ia_valid & ATTR_CTIME)
+		inode_set_ctime_to_ts(inode, attr->ia_ctime);
 }
 EXPORT_SYMBOL(setattr_copy);