dcache: d_splice_alias mustn't create directory aliases (908790fa) · Commits · 戴 / test

Currently if d_splice_alias finds a directory with an alias that is not IS_ROOT or not DCACHE_DISCONNECTED, it creates a duplicate directory. Duplicate directory dentries are unacceptable; it is better just to error out. (In the case of a local filesystem the most likely case is filesystem corruption: for example, perhaps two directories point to the same child directory, and the other parent has already been found and cached.) Note that distributed filesystems may encounter this case in normal operation if a remote host moves a directory to a location different from the one we last cached in the dcache. For that reason, such filesystems should instead use d_materialise_unique, which tries to move the old directory alias to the right place instead of erroring out. Signed-off-by:

J. Bruce Fields <bfields@redhat.com> Signed-off-by:

Al Viro <viro@zeniv.linux.org.uk>

fs/dcache.c

+9 −2

Original line number	Diff line number	Diff line
		@@ -2653,6 +2653,9 @@ static void __d_materialise_dentry(struct dentry dentry, struct dentry anon)
		* DCACHE_DISCONNECTED), then d_move that in place of the given dentry
		* and return it, else simply d_add the inode to the dentry and return NULL.
		*
		* If a non-IS_ROOT directory is found, the filesystem is corrupt, and
		* we should error out: directories can't have multiple aliases.
		*
		* This is needed in the lookup routine of any filesystem that is exportable
		* (via knfsd) so that we can build dcache paths to directories effectively.
		*
		@@ -2673,9 +2676,13 @@ struct dentry d_splice_alias(struct inode inode, struct dentry *dentry)

		if (inode && S_ISDIR(inode->i_mode)) {
		spin_lock(&inode->i_lock);
		new = __d_find_alias(inode, 1);
		new = __d_find_any_alias(inode);
		if (new) {
		BUG_ON(!(new->d_flags & DCACHE_DISCONNECTED));
		if (!IS_ROOT(new) \|\| !(new->d_flags & DCACHE_DISCONNECTED)) {
		spin_unlock(&inode->i_lock);
		dput(new);
		return ERR_PTR(-EIO);
		}
		write_seqlock(&rename_lock);
		__d_materialise_dentry(dentry, new);
		write_sequnlock(&rename_lock);

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