[PATCH v5 1/4] fs: add icount_read_once() and stop open-coding ->i_count loads

[Mateusz Guzik <mjguzik@gmail.com>]

Similarly to inode_state_read_once(), it makes the caller spell out
they acknowledge instability of the returned value.

Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
---
 arch/powerpc/platforms/cell/spufs/file.c |  2 +-
 fs/btrfs/inode.c                         |  2 +-
 fs/ceph/mds_client.c                     |  2 +-
 fs/ext4/ialloc.c                         |  4 ++--
 fs/hpfs/inode.c                          |  2 +-
 fs/inode.c                               | 12 ++++++------
 fs/nfs/inode.c                           |  4 ++--
 fs/smb/client/inode.c                    |  2 +-
 fs/ubifs/super.c                         |  2 +-
 fs/xfs/xfs_inode.c                       |  2 +-
 fs/xfs/xfs_trace.h                       |  2 +-
 include/linux/fs.h                       | 13 +++++++++++++
 include/trace/events/filelock.h          |  2 +-
 security/landlock/fs.c                   |  2 +-
 14 files changed, 33 insertions(+), 20 deletions(-)

diff --git a/arch/powerpc/platforms/cell/spufs/file.c b/arch/powerpc/platforms/cell/spufs/file.c
index 10fa9b844fcc..f6de8c1169d5 100644
--- a/arch/powerpc/platforms/cell/spufs/file.c
+++ b/arch/powerpc/platforms/cell/spufs/file.c
@@ -1430,7 +1430,7 @@ static int spufs_mfc_open(struct inode *inode, struct file *file)
 	if (ctx->owner != current->mm)
 		return -EINVAL;
 
-	if (icount_read(inode) != 1)
+	if (icount_read_once(inode) != 1)
 		return -EBUSY;
 
 	mutex_lock(&ctx->mapping_lock);
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 8d97a8ad3858..f36c49e83c04 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -4741,7 +4741,7 @@ static void btrfs_prune_dentries(struct btrfs_root *root)
 
 	inode = btrfs_find_first_inode(root, min_ino);
 	while (inode) {
-		if (icount_read(&inode->vfs_inode) > 1)
+		if (icount_read_once(&inode->vfs_inode) > 1)
 			d_prune_aliases(&inode->vfs_inode);
 
 		min_ino = btrfs_ino(inode) + 1;
diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index b1746273f186..2cb3c919d40d 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -2223,7 +2223,7 @@ static int trim_caps_cb(struct inode *inode, int mds, void *arg)
 			int count;
 			dput(dentry);
 			d_prune_aliases(inode);
-			count = icount_read(inode);
+			count = icount_read_once(inode);
 			if (count == 1)
 				(*remaining)--;
 			doutc(cl, "%p %llx.%llx cap %p pruned, count now %d\n",
diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 3fd8f0099852..8c80d5087516 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -252,10 +252,10 @@ void ext4_free_inode(handle_t *handle, struct inode *inode)
 		       "nonexistent device\n", __func__, __LINE__);
 		return;
 	}
-	if (icount_read(inode) > 1) {
+	if (icount_read_once(inode) > 1) {
 		ext4_msg(sb, KERN_ERR, "%s:%d: inode #%llu: count=%d",
 			 __func__, __LINE__, inode->i_ino,
-			 icount_read(inode));
+			 icount_read_once(inode));
 		return;
 	}
 	if (inode->i_nlink) {
diff --git a/fs/hpfs/inode.c b/fs/hpfs/inode.c
index 0e932cc8be1b..1b4fcf760aad 100644
--- a/fs/hpfs/inode.c
+++ b/fs/hpfs/inode.c
@@ -184,7 +184,7 @@ void hpfs_write_inode(struct inode *i)
 	struct hpfs_inode_info *hpfs_inode = hpfs_i(i);
 	struct inode *parent;
 	if (i->i_ino == hpfs_sb(i->i_sb)->sb_root) return;
-	if (hpfs_inode->i_rddir_off && !icount_read(i)) {
+	if (hpfs_inode->i_rddir_off && !icount_read_once(i)) {
 		if (*hpfs_inode->i_rddir_off)
 			pr_err("write_inode: some position still there\n");
 		kfree(hpfs_inode->i_rddir_off);
diff --git a/fs/inode.c b/fs/inode.c
index 5ad169d51728..1f5a383ccf27 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -907,7 +907,7 @@ void evict_inodes(struct super_block *sb)
 again:
 	spin_lock(&sb->s_inode_list_lock);
 	list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
-		if (icount_read(inode))
+		if (icount_read_once(inode))
 			continue;
 
 		spin_lock(&inode->i_lock);
@@ -1926,7 +1926,7 @@ static void iput_final(struct inode *inode)
 	int drop;
 
 	WARN_ON(inode_state_read(inode) & I_NEW);
-	VFS_BUG_ON_INODE(atomic_read(&inode->i_count) != 0, inode);
+	VFS_BUG_ON_INODE(icount_read(inode) != 0, inode);
 
 	if (op->drop_inode)
 		drop = op->drop_inode(inode);
@@ -1945,7 +1945,7 @@ static void iput_final(struct inode *inode)
 	 * Re-check ->i_count in case the ->drop_inode() hooks played games.
 	 * Note we only execute this if the verdict was to drop the inode.
 	 */
-	VFS_BUG_ON_INODE(atomic_read(&inode->i_count) != 0, inode);
+	VFS_BUG_ON_INODE(icount_read(inode) != 0, inode);
 
 	if (drop) {
 		inode_state_set(inode, I_FREEING);
@@ -1989,7 +1989,7 @@ void iput(struct inode *inode)
 	 * equal to one, then two CPUs racing to further drop it can both
 	 * conclude it's fine.
 	 */
-	VFS_BUG_ON_INODE(atomic_read(&inode->i_count) < 1, inode);
+	VFS_BUG_ON_INODE(icount_read_once(inode) < 1, inode);
 
 	if (atomic_add_unless(&inode->i_count, -1, 1))
 		return;
@@ -2023,7 +2023,7 @@ EXPORT_SYMBOL(iput);
 void iput_not_last(struct inode *inode)
 {
 	VFS_BUG_ON_INODE(inode_state_read_once(inode) & (I_FREEING | I_CLEAR), inode);
-	VFS_BUG_ON_INODE(atomic_read(&inode->i_count) < 2, inode);
+	VFS_BUG_ON_INODE(icount_read_once(inode) < 2, inode);
 
 	WARN_ON(atomic_sub_return(1, &inode->i_count) == 0);
 }
@@ -3046,7 +3046,7 @@ void dump_inode(struct inode *inode, const char *reason)
 	}
 
 	state = inode_state_read_once(inode);
-	count = atomic_read(&inode->i_count);
+	count = icount_read_once(inode);
 
 	if (!sb ||
 	    get_kernel_nofault(s_type, &sb->s_type) || !s_type ||
diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index 98a8f0de1199..22834eddd5b1 100644
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -608,7 +608,7 @@ nfs_fhget(struct super_block *sb, struct nfs_fh *fh, struct nfs_fattr *fattr)
 		inode->i_sb->s_id,
 		(unsigned long long)NFS_FILEID(inode),
 		nfs_display_fhandle_hash(fh),
-		icount_read(inode));
+		icount_read_once(inode));
 
 out:
 	return inode;
@@ -2261,7 +2261,7 @@ static int nfs_update_inode(struct inode *inode, struct nfs_fattr *fattr)
 	dfprintk(VFS, "NFS: %s(%s/%llu fh_crc=0x%08x ct=%d info=0x%llx)\n",
 			__func__, inode->i_sb->s_id, inode->i_ino,
 			nfs_display_fhandle_hash(NFS_FH(inode)),
-			icount_read(inode), fattr->valid);
+			icount_read_once(inode), fattr->valid);
 
 	if (!(fattr->valid & NFS_ATTR_FATTR_FILEID)) {
 		/* Only a mounted-on-fileid? Just exit */
diff --git a/fs/smb/client/inode.c b/fs/smb/client/inode.c
index 888f9e35f14b..ab35e35b16d7 100644
--- a/fs/smb/client/inode.c
+++ b/fs/smb/client/inode.c
@@ -2842,7 +2842,7 @@ int cifs_revalidate_dentry_attr(struct dentry *dentry)
 	}
 
 	cifs_dbg(FYI, "Update attributes: %s inode 0x%p count %d dentry: 0x%p d_time %ld jiffies %ld\n",
-		 full_path, inode, icount_read(inode),
+		 full_path, inode, icount_read_once(inode),
 		 dentry, cifs_get_time(dentry), jiffies);
 
 again:
diff --git a/fs/ubifs/super.c b/fs/ubifs/super.c
index 9a77d8b64ffa..38972786817e 100644
--- a/fs/ubifs/super.c
+++ b/fs/ubifs/super.c
@@ -358,7 +358,7 @@ static void ubifs_evict_inode(struct inode *inode)
 		goto out;
 
 	dbg_gen("inode %llu, mode %#x", inode->i_ino, (int)inode->i_mode);
-	ubifs_assert(c, !icount_read(inode));
+	ubifs_assert(c, !icount_read_once(inode));
 
 	truncate_inode_pages_final(&inode->i_data);
 
diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index beaa26ec62da..4f659eba6ae5 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -1046,7 +1046,7 @@ xfs_itruncate_extents_flags(
 	int			error = 0;
 
 	xfs_assert_ilocked(ip, XFS_ILOCK_EXCL);
-	if (icount_read(VFS_I(ip)))
+	if (icount_read_once(VFS_I(ip)))
 		xfs_assert_ilocked(ip, XFS_IOLOCK_EXCL);
 	if (whichfork == XFS_DATA_FORK)
 		ASSERT(new_size <= XFS_ISIZE(ip));
diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
index 5e8190fe2be9..cbdec40826b3 100644
--- a/fs/xfs/xfs_trace.h
+++ b/fs/xfs/xfs_trace.h
@@ -1156,7 +1156,7 @@ DECLARE_EVENT_CLASS(xfs_iref_class,
 	TP_fast_assign(
 		__entry->dev = VFS_I(ip)->i_sb->s_dev;
 		__entry->ino = ip->i_ino;
-		__entry->count = icount_read(VFS_I(ip));
+		__entry->count = icount_read_once(VFS_I(ip));
 		__entry->pincount = atomic_read(&ip->i_pincount);
 		__entry->iflags = ip->i_flags;
 		__entry->caller_ip = caller_ip;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 8afbe2ef2686..07363fce4406 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2225,8 +2225,21 @@ static inline void mark_inode_dirty_sync(struct inode *inode)
 	__mark_inode_dirty(inode, I_DIRTY_SYNC);
 }
 
+/*
+ * returns the refcount on the inode. it can change arbitrarily.
+ */
+static inline int icount_read_once(const struct inode *inode)
+{
+	return atomic_read(&inode->i_count);
+}
+
+/*
+ * returns the refcount on the inode. The lock guarantees no new references
+ * are added, but references can be dropped as long as the result is > 0.
+ */
 static inline int icount_read(const struct inode *inode)
 {
+	lockdep_assert_held(&inode->i_lock);
 	return atomic_read(&inode->i_count);
 }
 
diff --git a/include/trace/events/filelock.h b/include/trace/events/filelock.h
index 116774886244..c8c8847bb6f6 100644
--- a/include/trace/events/filelock.h
+++ b/include/trace/events/filelock.h
@@ -190,7 +190,7 @@ TRACE_EVENT(generic_add_lease,
 		__entry->i_ino = inode->i_ino;
 		__entry->wcount = atomic_read(&inode->i_writecount);
 		__entry->rcount = atomic_read(&inode->i_readcount);
-		__entry->icount = icount_read(inode);
+		__entry->icount = icount_read_once(inode);
 		__entry->owner = fl->c.flc_owner;
 		__entry->flags = fl->c.flc_flags;
 		__entry->type = fl->c.flc_type;
diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index c1ecfe239032..32d560f12dbd 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -1278,7 +1278,7 @@ static void hook_sb_delete(struct super_block *const sb)
 		struct landlock_object *object;
 
 		/* Only handles referenced inodes. */
-		if (!icount_read(inode))
+		if (!icount_read_once(inode))
 			continue;
 
 		/*
-- 
2.48.1