Merge patch series "fs: add iput_not_last()"

Add iput_not_last() and switch landlock over to it to remove
false-positives from might_sleep() annotations in iput().

Link: https://patch.msgid.link/[email protected]

* patches from https://patch.msgid.link/[email protected]:
  landlock: fix splats from iput() after it started calling might_sleep()
  fs: add iput_not_last()

Signed-off-by: Christian Brauner <[email protected]>

Author: brauner

fs/inode.c

@@ -1967,6 +1967,18 @@ void iput(struct inode *inode)
 }
 EXPORT_SYMBOL(iput);
 
+/**
+ *	iput_not_last	- put an inode assuming this is not the last reference
+ *	@inode: inode to put
+ */
+void iput_not_last(struct inode *inode)
+{
+	VFS_BUG_ON_INODE(atomic_read(&inode->i_count) < 2, inode);
+
+	WARN_ON(atomic_sub_return(1, &inode->i_count) == 0);
+}
+EXPORT_SYMBOL(iput_not_last);
+
 #ifdef CONFIG_BLOCK
 /**
  *	bmap	- find a block number in a file

include/linux/fs.h

@@ -2824,6 +2824,7 @@ extern int current_umask(void);
 
 extern void ihold(struct inode * inode);
 extern void iput(struct inode *);
+void iput_not_last(struct inode *);
 int inode_update_timestamps(struct inode *inode, int flags);
 int generic_update_time(struct inode *, int);
 

security/landlock/fs.c

@@ -1335,11 +1335,10 @@ static void hook_sb_delete(struct super_block *const sb)
 			 * At this point, we own the ihold() reference that was
 			 * originally set up by get_inode_object() and the
 			 * __iget() reference that we just set in this loop
-			 * walk.  Therefore the following call to iput() will
-			 * not sleep nor drop the inode because there is now at
-			 * least two references to it.
+			 * walk.  Therefore there are at least two references
+			 * on the inode.
 			 */
-			iput(inode);
+			iput_not_last(inode);
 		} else {
 			spin_unlock(&object->lock);
 			rcu_read_unlock();