vfs: rename parent_ino to d_parent_ino and make it use RCU

The routine is used by procfs through dir_emit_dots.

The combined RCU and lock fallback implementation is too big for an
inline. Given that the routine takes a dentry argument fs/dcache.c seems
like the place to put it in.

Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Link: https://lore.kernel.org/r/20240627161152.802567-1-mjguzik@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

5 files changed, 34 insertions, 18 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index 58b89c9e9b0c..68e843e78337 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -3099,6 +3099,34 @@ void d_tmpfile(struct file *file, struct inode *inode)
 }
 EXPORT_SYMBOL(d_tmpfile);
 
+/*
+ * Obtain inode number of the parent dentry.
+ */
+ino_t d_parent_ino(struct dentry *dentry)
+{
+	struct dentry *parent;
+	struct inode *iparent;
+	unsigned seq;
+	ino_t ret;
+
+	scoped_guard(rcu) {
+		seq = raw_seqcount_begin(&dentry->d_seq);
+		parent = READ_ONCE(dentry->d_parent);
+		iparent = d_inode_rcu(parent);
+		if (likely(iparent)) {
+			ret = iparent->i_ino;
+			if (!read_seqcount_retry(&dentry->d_seq, seq))
+				return ret;
+		}
+	}
+
+	spin_lock(&dentry->d_lock);
+	ret = dentry->d_parent->d_inode->i_ino;
+	spin_unlock(&dentry->d_lock);
+	return ret;
+}
+EXPORT_SYMBOL(d_parent_ino);
+
 static __initdata unsigned long dhash_entries;
 static int __init set_dhash_entries(char *str)
 {
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 7a23434963d1..c1ad9b278c47 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -185,7 +185,7 @@ static int get_parent_ino(struct inode *inode, nid_t *pino)
 	if (!dentry)
 		return 0;
 
-	*pino = parent_ino(dentry);
+	*pino = d_parent_ino(dentry);
 	dput(dentry);
 	return 1;
 }
diff --git a/fs/hfsplus/ioctl.c b/fs/hfsplus/ioctl.c
index 5661a2e24d03..40d04dba13ac 100644
--- a/fs/hfsplus/ioctl.c
+++ b/fs/hfsplus/ioctl.c
@@ -40,7 +40,7 @@ static int hfsplus_ioctl_bless(struct file *file, int __user *user_flags)
 
 	/* Directory containing the bootable system */
 	vh->finder_info[0] = bvh->finder_info[0] =
-		cpu_to_be32(parent_ino(dentry));
+		cpu_to_be32(d_parent_ino(dentry));
 
 	/*
 	 * Bootloader. Just using the inode here breaks in the case of
@@ -51,7 +51,7 @@ static int hfsplus_ioctl_bless(struct file *file, int __user *user_flags)
 
 	/* Per spec, the OS X system folder - same as finder_info[0] here */
 	vh->finder_info[5] = bvh->finder_info[5] =
-		cpu_to_be32(parent_ino(dentry));
+		cpu_to_be32(d_parent_ino(dentry));
 
 	mutex_unlock(&sbi->vh_mutex);
 	return 0;
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index bf53e3894aae..ea58843942b9 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -278,6 +278,8 @@ static inline unsigned d_count(const struct dentry *dentry)
 	return dentry->d_lockref.count;
 }
 
+ino_t d_parent_ino(struct dentry *dentry);
+
 /*
  * helper function for dentry_operations.d_dname() members
  */
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 5ff362277834..2fa06a4d197a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3454,20 +3454,6 @@ static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
 	return 0;
 }
 
-static inline ino_t parent_ino(struct dentry *dentry)
-{
-	ino_t res;
-
-	/*
-	 * Don't strictly need d_lock here? If the parent ino could change
-	 * then surely we'd have a deeper race in the caller?
-	 */
-	spin_lock(&dentry->d_lock);
-	res = dentry->d_parent->d_inode->i_ino;
-	spin_unlock(&dentry->d_lock);
-	return res;
-}
-
 /* Transaction based IO helpers */
 
 /*
@@ -3592,7 +3578,7 @@ static inline bool dir_emit_dot(struct file *file, struct dir_context *ctx)
 static inline bool dir_emit_dotdot(struct file *file, struct dir_context *ctx)
 {
 	return ctx->actor(ctx, "..", 2, ctx->pos,
-			  parent_ino(file->f_path.dentry), DT_DIR);
+			  d_parent_ino(file->f_path.dentry), DT_DIR);
 }
 static inline bool dir_emit_dots(struct file *file, struct dir_context *ctx)
 {