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Message-Id: <20241002-mgtime-v10-5-d1c4717f5284@kernel.org>
Date: Wed, 02 Oct 2024 17:27:20 -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 v10 05/12] fs: handle delegated timestamps in
setattr_copy_mgtime
An update to the inode ctime typically requires the latest clock
value possible. The exception to this rule is when there is a nfsd write
delegation and the server is proxying timestamps from the client.
When nfsd gets a CB_GETATTR response, update the timestamp value in the
inode to the values that the client is tracking. The client doesn't send
a ctime value (since that's always determined by the exported
filesystem), but it can send a mtime value. In the case where it does,
update the ctime to a value commensurate with that instead of the
current time.
If ATTR_DELEG is set, then use ia_ctime value instead of setting the
timestamp to the current time.
With the addition of delegated timestamps, the server may receive a
request to update only the atime, which doesn't involve a ctime update.
Trust the ATTR_CTIME flag in the update and only update the ctime when
it's set.
Tested-by: Randy Dunlap <rdunlap@...radead.org> # documentation bits
Reviewed-by: Jan Kara <jack@...e.cz>
Signed-off-by: Jeff Layton <jlayton@...nel.org>
---
fs/attr.c | 28 +++++++++++++--------
fs/inode.c | 73 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/fs.h | 2 ++
3 files changed, 93 insertions(+), 10 deletions(-)
diff --git a/fs/attr.c b/fs/attr.c
index 0309c2bd8afa04bc43db6ff207f8a58d9f6a617d..c614b954bda5244cc20ee82a98a8e68845f23bd7 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -286,16 +286,20 @@ 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;
+ if (ia_valid & ATTR_CTIME) {
+ /*
+ * In the case of an update for a write delegation, we must respect
+ * the value in ia_ctime and not use the current time.
+ */
+ if (ia_valid & ATTR_DELEG)
+ now = inode_set_ctime_deleg(inode, attr->ia_ctime);
+ else
+ now = inode_set_ctime_current(inode);
+ } else {
+ /* If ATTR_CTIME isn't set, then ATTR_MTIME shouldn't be either. */
+ WARN_ON_ONCE(ia_valid & ATTR_MTIME);
}
- 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)
@@ -354,8 +358,12 @@ void setattr_copy(struct mnt_idmap *idmap, struct inode *inode,
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_CTIME) {
+ if (ia_valid & ATTR_DELEG)
+ inode_set_ctime_deleg(inode, attr->ia_ctime);
+ else
+ inode_set_ctime_to_ts(inode, attr->ia_ctime);
+ }
}
EXPORT_SYMBOL(setattr_copy);
diff --git a/fs/inode.c b/fs/inode.c
index 53f56f6e1ff26e718080211880924f37cf0e5b3c..7d1ede60e549683502911f3bb3a3a079768e449b 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -2717,6 +2717,79 @@ struct timespec64 inode_set_ctime_current(struct inode *inode)
}
EXPORT_SYMBOL(inode_set_ctime_current);
+/**
+ * inode_set_ctime_deleg - try to update the ctime on a delegated inode
+ * @inode: inode to update
+ * @update: timespec64 to set the ctime
+ *
+ * Attempt to atomically update the ctime on behalf of a delegation holder.
+ *
+ * The nfs server can call back the holder of a delegation to get updated
+ * inode attributes, including the mtime. When updating the mtime, update
+ * the ctime to a value at least equal to that.
+ *
+ * This can race with concurrent updates to the inode, in which
+ * case the update is skipped.
+ *
+ * Note that this works even when multigrain timestamps are not enabled,
+ * so it is used in either case.
+ */
+struct timespec64 inode_set_ctime_deleg(struct inode *inode, struct timespec64 update)
+{
+ struct timespec64 now, cur_ts;
+ u32 cur, old;
+
+ /* pairs with try_cmpxchg below */
+ cur = smp_load_acquire(&inode->i_ctime_nsec);
+ cur_ts.tv_nsec = cur & ~I_CTIME_QUERIED;
+ cur_ts.tv_sec = inode->i_ctime_sec;
+
+ /* If the update is older than the existing value, skip it. */
+ if (timespec64_compare(&update, &cur_ts) <= 0)
+ return cur_ts;
+
+ ktime_get_coarse_real_ts64_mg(&now);
+
+ /* Clamp the update to "now" if it's in the future */
+ if (timespec64_compare(&update, &now) > 0)
+ update = now;
+
+ update = timestamp_truncate(update, inode);
+
+ /* No need to update if the values are already the same */
+ if (timespec64_equal(&update, &cur_ts))
+ return cur_ts;
+
+ /*
+ * Try to swap the nsec value into place. If it fails, that means
+ * it raced with an update due to a write or similar activity. That
+ * stamp takes precedence, so just skip the update.
+ */
+retry:
+ old = cur;
+ if (try_cmpxchg(&inode->i_ctime_nsec, &cur, update.tv_nsec)) {
+ inode->i_ctime_sec = update.tv_sec;
+ mgtime_counter_inc(mg_ctime_swaps);
+ return update;
+ }
+
+ /*
+ * Was the change due to another task marking the old ctime QUERIED?
+ *
+ * If so, then retry the swap. This can only happen once since
+ * the only way to clear I_CTIME_QUERIED is to stamp the inode
+ * with a new ctime.
+ */
+ if (!(old & I_CTIME_QUERIED) && (cur == (old | I_CTIME_QUERIED)))
+ goto retry;
+
+ /* Otherwise, it was a new timestamp. */
+ cur_ts.tv_sec = inode->i_ctime_sec;
+ cur_ts.tv_nsec = cur & ~I_CTIME_QUERIED;
+ return cur_ts;
+}
+EXPORT_SYMBOL(inode_set_ctime_deleg);
+
/**
* in_group_or_capable - check whether caller is CAP_FSETID privileged
* @idmap: idmap of the mount @inode was found from
diff --git a/include/linux/fs.h b/include/linux/fs.h
index eff688e75f2f29f1c44dca96370ee230f8c21db4..ea7ed437d2b165debf680507aa450b2662fd5839 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1544,6 +1544,8 @@ static inline bool fsuidgid_has_mapping(struct super_block *sb,
struct timespec64 current_time(struct inode *inode);
struct timespec64 inode_set_ctime_current(struct inode *inode);
+struct timespec64 inode_set_ctime_deleg(struct inode *inode,
+ struct timespec64 update);
static inline time64_t inode_get_atime_sec(const struct inode *inode)
{
--
2.46.2
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