linux-ext4 - [PATCH v2 22/54] fs: convert i_count to refcount

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Message-ID: <36a888e4cf47948c01f49ee24ede2b662075fc5e.1756222465.git.josef@toxicpanda.com>
Date: Tue, 26 Aug 2025 11:39:22 -0400
From: Josef Bacik <josef@...icpanda.com>
To: linux-fsdevel@...r.kernel.org,
	linux-btrfs@...r.kernel.org,
	kernel-team@...com,
	linux-ext4@...r.kernel.org,
	linux-xfs@...r.kernel.org,
	brauner@...nel.org,
	viro@...IV.linux.org.uk,
	amir73il@...il.com
Subject: [PATCH v2 22/54] fs: convert i_count to refcount_t

Now that we do not allow i_count to drop to 0 and be used we can convert
it to a refcount_t and benefit from the protections those helpers add.

Signed-off-by: Josef Bacik <josef@...icpanda.com>
---
 fs/btrfs/inode.c   | 2 +-
 fs/inode.c         | 9 +++++----
 include/linux/fs.h | 6 +++---
 3 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index e16df38e0eef..eb9496342346 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -3418,7 +3418,7 @@ void btrfs_add_delayed_iput(struct btrfs_inode *inode)
 	struct btrfs_fs_info *fs_info = inode->root->fs_info;
 	unsigned long flags;
 
-	if (atomic_add_unless(&inode->vfs_inode.i_count, -1, 1)) {
+	if (refcount_dec_not_one(&inode->vfs_inode.i_count)) {
 		iobj_put(&inode->vfs_inode);
 		return;
 	}
diff --git a/fs/inode.c b/fs/inode.c
index 1992db5cd70a..0be1c137bf1e 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -236,7 +236,7 @@ int inode_init_always_gfp(struct super_block *sb, struct inode *inode, gfp_t gfp
 	inode->i_state = 0;
 	atomic64_set(&inode->i_sequence, 0);
 	refcount_set(&inode->i_obj_count, 1);
-	atomic_set(&inode->i_count, 1);
+	refcount_set(&inode->i_count, 1);
 	inode->i_op = &empty_iops;
 	inode->i_fop = &no_open_fops;
 	inode->i_ino = 0;
@@ -545,7 +545,8 @@ static void init_once(void *foo)
 void ihold(struct inode *inode)
 {
 	iobj_get(inode);
-	WARN_ON(atomic_inc_return(&inode->i_count) < 2);
+	refcount_inc(&inode->i_count);
+	WARN_ON(icount_read(inode) < 2);
 }
 EXPORT_SYMBOL(ihold);
 
@@ -2011,7 +2012,7 @@ static void __iput(struct inode *inode, bool skip_lru)
 		return;
 	BUG_ON(inode->i_state & I_CLEAR);
 
-	if (atomic_add_unless(&inode->i_count, -1, 1)) {
+	if (refcount_dec_not_one(&inode->i_count)) {
 		iobj_put(inode);
 		return;
 	}
@@ -2031,7 +2032,7 @@ static void __iput(struct inode *inode, bool skip_lru)
 	 */
 	drop = maybe_add_lru(inode, skip_lru);
 
-	if (atomic_dec_and_test(&inode->i_count)) {
+	if (refcount_dec_and_test(&inode->i_count)) {
 		/* iput_final() drops i_lock */
 		iput_final(inode, drop);
 	} else {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 999ffea2aac1..fc23e37ca250 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -875,7 +875,7 @@ struct inode {
 	};
 	atomic64_t		i_version;
 	atomic64_t		i_sequence; /* see futex */
-	atomic_t		i_count;
+	refcount_t		i_count;
 	atomic_t		i_dio_count;
 	atomic_t		i_writecount;
 #if defined(CONFIG_IMA) || defined(CONFIG_FILE_LOCKING)
@@ -3399,12 +3399,12 @@ static inline unsigned int iobj_count_read(const struct inode *inode)
 static inline void __iget(struct inode *inode)
 {
 	iobj_get(inode);
-	atomic_inc(&inode->i_count);
+	refcount_inc(&inode->i_count);
 }
 
 static inline int icount_read(const struct inode *inode)
 {
-	return atomic_read(&inode->i_count);
+	return refcount_read(&inode->i_count);
 }
 
 extern void iget_failed(struct inode *);
-- 
2.49.0