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From:   Al Viro <viro@zeniv.linux.org.uk>
To:     linux-fsdevel@vger.kernel.org
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Mo Zou <lostzoumo@gmail.com>, Jan Kara <jack@suse.cz>,
        linux-kernel@vger.kernel.org
Subject: [PATCH v2 5/9] ext4: don't access the source subdirectory content on same-directory rename
Date:   Sat, 25 Nov 2023 20:11:43 +0000
Message-Id: <20231125201147.753695-5-viro@zeniv.linux.org.uk>
In-Reply-To: <20231125201147.753695-1-viro@zeniv.linux.org.uk>
References: <20231125201015.GA38156@ZenIV>
 <20231125201147.753695-1-viro@zeniv.linux.org.uk>
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Sender: Al Viro <viro@ftp.linux.org.uk>
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We can't really afford locking the source on same-directory rename;
currently vfs_rename() tries to do that, but it will have to be changed.
The logics in ext4 is lazy and goes looking for ".." in source even in
same-directory case.  It's not hard to get rid of that, leaving that
behaviour only for cross-directory case; that VFS can get locks safely
(and will keep doing that after the coming changes).

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/ext4/namei.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index d252935f9c8a..467ba47a691c 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -3591,10 +3591,14 @@ struct ext4_renament {
 	int dir_inlined;
 };
 
-static int ext4_rename_dir_prepare(handle_t *handle, struct ext4_renament *ent)
+static int ext4_rename_dir_prepare(handle_t *handle, struct ext4_renament *ent, bool is_cross)
 {
 	int retval;
 
+	ent->is_dir = true;
+	if (!is_cross)
+		return 0;
+
 	ent->dir_bh = ext4_get_first_dir_block(handle, ent->inode,
 					      &retval, &ent->parent_de,
 					      &ent->dir_inlined);
@@ -3612,6 +3616,9 @@ static int ext4_rename_dir_finish(handle_t *handle, struct ext4_renament *ent,
 {
 	int retval;
 
+	if (!ent->dir_bh)
+		return 0;
+
 	ent->parent_de->inode = cpu_to_le32(dir_ino);
 	BUFFER_TRACE(ent->dir_bh, "call ext4_handle_dirty_metadata");
 	if (!ent->dir_inlined) {
@@ -3900,7 +3907,7 @@ static int ext4_rename(struct mnt_idmap *idmap, struct inode *old_dir,
 			if (new.dir != old.dir && EXT4_DIR_LINK_MAX(new.dir))
 				goto end_rename;
 		}
-		retval = ext4_rename_dir_prepare(handle, &old);
+		retval = ext4_rename_dir_prepare(handle, &old, new.dir != old.dir);
 		if (retval)
 			goto end_rename;
 	}
@@ -3964,7 +3971,7 @@ static int ext4_rename(struct mnt_idmap *idmap, struct inode *old_dir,
 	}
 	inode_set_mtime_to_ts(old.dir, inode_set_ctime_current(old.dir));
 	ext4_update_dx_flag(old.dir);
-	if (old.dir_bh) {
+	if (old.is_dir) {
 		retval = ext4_rename_dir_finish(handle, &old, new.dir->i_ino);
 		if (retval)
 			goto end_rename;
@@ -3987,7 +3994,7 @@ static int ext4_rename(struct mnt_idmap *idmap, struct inode *old_dir,
 	if (unlikely(retval))
 		goto end_rename;
 
-	if (S_ISDIR(old.inode->i_mode)) {
+	if (old.is_dir) {
 		/*
 		 * We disable fast commits here that's because the
 		 * replay code is not yet capable of changing dot dot
@@ -4114,14 +4121,12 @@ static int ext4_cross_rename(struct inode *old_dir, struct dentry *old_dentry,
 		ext4_handle_sync(handle);
 
 	if (S_ISDIR(old.inode->i_mode)) {
-		old.is_dir = true;
-		retval = ext4_rename_dir_prepare(handle, &old);
+		retval = ext4_rename_dir_prepare(handle, &old, new.dir != old.dir);
 		if (retval)
 			goto end_rename;
 	}
 	if (S_ISDIR(new.inode->i_mode)) {
-		new.is_dir = true;
-		retval = ext4_rename_dir_prepare(handle, &new);
+		retval = ext4_rename_dir_prepare(handle, &new, new.dir != old.dir);
 		if (retval)
 			goto end_rename;
 	}
-- 
2.39.2