Revert "fs: add infrastructure for multigrain timestamps"

This reverts commit ffb6cf19e06334062744b7e3493f71e500964f8e.

Users reported regressions due to enabling multi-grained timestamps
unconditionally. As no clear consensus on a solution has come up and the
discussion has gone back to the drawing board revert the infrastructure
changes for. If it isn't code that's here to stay, make it go away.

Message-ID: <20230920-keine-eile-c9755b5825db@brauner>
Acked-by: Jan Kara <jack@suse.cz>
Acked-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

2 files changed, 5 insertions, 118 deletions

diff --git a/fs/inode.c b/fs/inode.c
index 35fd688168c5..84bc3c76e5cc 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -2102,52 +2102,10 @@ int file_remove_privs(struct file *file)
 }
 EXPORT_SYMBOL(file_remove_privs);
 
-/**
- * current_mgtime - Return FS time (possibly fine-grained)
- * @inode: inode.
- *
- * Return the current time truncated to the time granularity supported by
- * the fs, as suitable for a ctime/mtime change. If the ctime is flagged
- * as having been QUERIED, get a fine-grained timestamp.
- */
-struct timespec64 current_mgtime(struct inode *inode)
-{
-	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);
-		return timestamp_truncate(now, inode);
-	}
-
-	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 ctime. Just keep the existing value if so.
-	 */
-	ctime = inode_get_ctime(inode);
-	if (timespec64_compare(&ctime, &now) > 0)
-		now = ctime;
-
-	return now;
-}
-EXPORT_SYMBOL(current_mgtime);
-
-static struct timespec64 current_ctime(struct inode *inode)
-{
-	if (is_mgtime(inode))
-		return current_mgtime(inode);
-	return current_time(inode);
-}
-
 static int inode_needs_update_time(struct inode *inode)
 {
 	int sync_it = 0;
-	struct timespec64 now = current_ctime(inode);
+	struct timespec64 now = current_time(inode);
 	struct timespec64 ctime;
 
 	/* First try to exhaust all avenues to not sync */
@@ -2578,43 +2536,9 @@ EXPORT_SYMBOL(current_time);
  */
 struct timespec64 inode_set_ctime_current(struct inode *inode)
 {
-	struct timespec64 now;
-	struct timespec64 ctime;
-
-	ctime.tv_nsec = READ_ONCE(inode->__i_ctime.tv_nsec);
-	if (!(ctime.tv_nsec & I_CTIME_QUERIED)) {
-		now = current_time(inode);
+	struct timespec64 now = current_time(inode);
 
-		/* Just copy it into place if it's not multigrain */
-		if (!is_mgtime(inode)) {
-			inode_set_ctime_to_ts(inode, now);
-			return now;
-		}
-
-		/*
-		 * If we've recently updated with 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.tv_sec = inode->__i_ctime.tv_sec;
-		if (timespec64_compare(&ctime, &now) > 0)
-			return ctime;
-
-		/*
-		 * Ctime updates are usually protected by the inode_lock, but
-		 * we can still race with someone setting the QUERIED flag.
-		 * Try to swap the new nsec value into place. If it's changed
-		 * in the interim, then just go with a fine-grained timestamp.
-		 */
-		if (cmpxchg(&inode->__i_ctime.tv_nsec, ctime.tv_nsec,
-			    now.tv_nsec) != ctime.tv_nsec)
-			goto fine_grained;
-		inode->__i_ctime.tv_sec = now.tv_sec;
-		return now;
-	}
-fine_grained:
-	ktime_get_real_ts64(&now);
-	inode_set_ctime_to_ts(inode, timestamp_truncate(now, inode));
+	inode_set_ctime(inode, now.tv_sec, now.tv_nsec);
 	return now;
 }
 EXPORT_SYMBOL(inode_set_ctime_current);
diff --git a/fs/stat.c b/fs/stat.c
index 6e60389d6a15..d43a5cc1bfa4 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -27,37 +27,6 @@
 #include "mount.h"
 
 /**
- * fill_mg_cmtime - Fill in the mtime and ctime and flag ctime as QUERIED
- * @stat: where to store the resulting values
- * @request_mask: STATX_* values requested
- * @inode: inode from which to grab the c/mtime
- *
- * Given @inode, grab the ctime and mtime out if it and store the result
- * in @stat. When fetching the value, flag it as queried so the next write
- * will use a fine-grained timestamp.
- */
-void fill_mg_cmtime(struct kstat *stat, u32 request_mask, struct inode *inode)
-{
-	atomic_long_t *pnsec = (atomic_long_t *)&inode->__i_ctime.tv_nsec;
-
-	/* If neither time was requested, then don't report them */
-	if (!(request_mask & (STATX_CTIME|STATX_MTIME))) {
-		stat->result_mask &= ~(STATX_CTIME|STATX_MTIME);
-		return;
-	}
-
-	stat->mtime = inode->i_mtime;
-	stat->ctime.tv_sec = inode->__i_ctime.tv_sec;
-	/*
-	 * Atomically set the QUERIED flag and fetch the new value with
-	 * the flag masked off.
-	 */
-	stat->ctime.tv_nsec = atomic_long_fetch_or(I_CTIME_QUERIED, pnsec) &
-					~I_CTIME_QUERIED;
-}
-EXPORT_SYMBOL(fill_mg_cmtime);
-
-/**
  * generic_fillattr - Fill in the basic attributes from the inode struct
  * @idmap:		idmap of the mount the inode was found from
  * @request_mask:	statx request_mask
@@ -89,14 +58,8 @@ void generic_fillattr(struct mnt_idmap *idmap, u32 request_mask,
 	stat->rdev = inode->i_rdev;
 	stat->size = i_size_read(inode);
 	stat->atime = inode->i_atime;
-
-	if (is_mgtime(inode)) {
-		fill_mg_cmtime(stat, request_mask, inode);
-	} else {
-		stat->mtime = inode->i_mtime;
-		stat->ctime = inode_get_ctime(inode);
-	}
-
+	stat->mtime = inode->i_mtime;
+	stat->ctime = inode_get_ctime(inode);
 	stat->blksize = i_blocksize(inode);
 	stat->blocks = inode->i_blocks;