linux-ext4 - [PATCH v9 03/12] fs: have setattr_copy handle multigrain timestamps appropriately

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Message-Id: <20241002-mgtime-v9-3-77e2baad57ac@kernel.org>
Date: Wed, 02 Oct 2024 14:49:31 -0400
From: Jeff Layton <jlayton@...nel.org>
To: John Stultz <jstultz@...gle.com>, Thomas Gleixner <tglx@...utronix.de>, 
 Stephen Boyd <sboyd@...nel.org>, Alexander Viro <viro@...iv.linux.org.uk>, 
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
 Steven Rostedt <rostedt@...dmis.org>, 
 Masami Hiramatsu <mhiramat@...nel.org>, 
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 
 Jonathan Corbet <corbet@....net>, Randy Dunlap <rdunlap@...radead.org>, 
 Chandan Babu R <chandan.babu@...cle.com>, 
 "Darrick J. Wong" <djwong@...nel.org>, Theodore Ts'o <tytso@....edu>, 
 Andreas Dilger <adilger.kernel@...ger.ca>, Chris Mason <clm@...com>, 
 Josef Bacik <josef@...icpanda.com>, David Sterba <dsterba@...e.com>, 
 Hugh Dickins <hughd@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, 
 Chuck Lever <chuck.lever@...cle.com>, 
 Vadim Fedorenko <vadim.fedorenko@...ux.dev>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
 linux-trace-kernel@...r.kernel.org, linux-doc@...r.kernel.org, 
 linux-xfs@...r.kernel.org, linux-ext4@...r.kernel.org, 
 linux-btrfs@...r.kernel.org, linux-nfs@...r.kernel.org, linux-mm@...ck.org, 
 Jeff Layton <jlayton@...nel.org>
Subject: [PATCH v9 03/12] fs: have setattr_copy handle multigrain
 timestamps appropriately

The setattr codepath is still using coarse-grained timestamps, even on
multigrain filesystems. To fix this, 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().

Do not 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@...nel.org>
Reviewed-by: Josef Bacik <josef@...icpanda.com>
Reviewed-by: Jan Kara <jack@...e.cz>
Tested-by: Randy Dunlap <rdunlap@...radead.org> # documentation bits
Signed-off-by: Jeff Layton <jlayton@...nel.org>
---
 fs/attr.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 46 insertions(+), 6 deletions(-)

diff --git a/fs/attr.c b/fs/attr.c
index c04d19b58f12..0309c2bd8afa 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, 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 those are being set 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);

-- 
2.46.2