[PATCH v7 04/11] fs: handle delegated timestamps in setattr_copy_mgtime

Jeff Layton
2024-09-13T13:54:31Z

When updating the ctime on an inode for a SETATTR with a multigrain
filesystem, we usually want to take the latest time we can get for the
ctime. 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, we want to 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, then we may need to 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 we can also receive a request
to update only the atime, but we may not need to set the ctime. Trust
the ATTR_CTIME flag in the update and only update the ctime when it's
set.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
fs/attr.c | 28 +++++++++++++--------
fs/inode.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/fs.h | 2 ++
3 files changed, 92 insertions(+), 10 deletions(-)

diff --git a/fs/attr.c b/fs/attr.c
index 3bcbc45708a3..392eb62aa609 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 8ab36779066e..260a8a1c1096 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -2710,6 +2710,78 @@ 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 we may
+ * need to update the ctime to a value at least equal to that.
+ *
+ * This can race with concurrent updates to the inode, in which
+ * case we just don't do the update.
+ *
+ * Note that this works even when multigrain timestamps are not enabled,
+ * so use it 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
+ * we 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 someone 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 eff688e75f2f..ea7ed437d2b1 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)
{

--
2.46.0