linux-kernel - [PATCH v13 08/59] fs: change test in inode

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Date:   Tue,  5 Apr 2022 15:19:39 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     idryomov@...il.com, xiubli@...hat.com
Cc:     ceph-devel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-fscrypt@...r.kernel.org, linux-kernel@...r.kernel.org,
        lhenriques@...e.de, Al Viro <viro@...iv.linux.org.uk>
Subject: [PATCH v13 08/59] fs: change test in inode_insert5 for adding to the sb list

The inode_insert5 currently looks at I_CREATING to decide whether to
insert the inode into the sb list. This test is a bit ambiguous though
as I_CREATING state is not directly related to that list.

This test is also problematic for some upcoming ceph changes to add
fscrypt support. We need to be able to allocate an inode using new_inode
and insert it into the hash later if we end up using it, and doing that
now means that we double add it and corrupt the list.

What we really want to know in this test is whether the inode is already
in its superblock list, and then add it if it isn't. Have it test for
list_empty instead and ensure that we always initialize the list by
doing it in inode_init_once. It's only ever removed from the list with
list_del_init, so that should be sufficient.

Suggested-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Jeff Layton <jlayton@...nel.org>
---
 fs/inode.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index 9d9b422504d1..743420a55e5f 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -422,6 +422,7 @@ void inode_init_once(struct inode *inode)
 	INIT_LIST_HEAD(&inode->i_io_list);
 	INIT_LIST_HEAD(&inode->i_wb_list);
 	INIT_LIST_HEAD(&inode->i_lru);
+	INIT_LIST_HEAD(&inode->i_sb_list);
 	__address_space_init_once(&inode->i_data);
 	i_size_ordered_init(inode);
 }
@@ -1021,7 +1022,6 @@ struct inode *new_inode_pseudo(struct super_block *sb)
 		spin_lock(&inode->i_lock);
 		inode->i_state = 0;
 		spin_unlock(&inode->i_lock);
-		INIT_LIST_HEAD(&inode->i_sb_list);
 	}
 	return inode;
 }
@@ -1165,7 +1165,6 @@ struct inode *inode_insert5(struct inode *inode, unsigned long hashval,
 {
 	struct hlist_head *head = inode_hashtable + hash(inode->i_sb, hashval);
 	struct inode *old;
-	bool creating = inode->i_state & I_CREATING;
 
 again:
 	spin_lock(&inode_hash_lock);
@@ -1199,7 +1198,13 @@ struct inode *inode_insert5(struct inode *inode, unsigned long hashval,
 	inode->i_state |= I_NEW;
 	hlist_add_head_rcu(&inode->i_hash, head);
 	spin_unlock(&inode->i_lock);
-	if (!creating)
+
+	/*
+	 * Add it to the list if it wasn't already in,
+	 * e.g. new_inode. We hold I_NEW at this point, so
+	 * we should be safe to test i_sb_list locklessly.
+	 */
+	if (list_empty(&inode->i_sb_list))
 		inode_sb_list_add(inode);
 unlock:
 	spin_unlock(&inode_hash_lock);
-- 
2.35.1