linux-kernel - [PATCH 3.2 44/74] ubifs: Correctly evict xattr inodes

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Message-ID: <lsq.1507552234.154332003@decadent.org.uk>
Date:   Mon, 09 Oct 2017 13:30:34 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Richard Weinberger" <richard@....at>
Subject: [PATCH 3.2 44/74] ubifs: Correctly evict xattr inodes

3.2.94-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Richard Weinberger <richard@....at>

commit 272eda8298dc82eb411ece82bbb2c62911087b24 upstream.

UBIFS handles extended attributes just like files, as consequence of
that, they also have inodes.
Therefore UBIFS does all the inode machinery also for xattrs. Since new
inodes have i_nlink of 1, a file or xattr inode will be evicted
if i_nlink goes down to 0 after an unlink. UBIFS assumes this model also
for xattrs, which is not correct.
One can create a file "foo" with xattr "user.test". By reading
"user.test" an inode will be created, and by deleting "user.test" it
will get evicted later. The assumption breaks if the file "foo", which
hosts the xattrs, will be removed. VFS nor UBIFS does not remove each
xattr via ubifs_xattr_remove(), it just removes the host inode from
the TNC and all underlying xattr nodes too and the inode will remain
in the cache and wastes memory.

To solve this problem, remove xattr inodes from the VFS inode cache in
ubifs_xattr_remove() to make sure that they get evicted.

Fixes: 1e51764a3c2ac05a ("UBIFS: add new flash file system")
Signed-off-by: Richard Weinberger <richard@....at>
[bwh: Backported to 3.2:
 - xattr support is optional, so add an #ifdef around the call
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
--- a/fs/ubifs/tnc.c
+++ b/fs/ubifs/tnc.c
@@ -2730,6 +2730,10 @@ int ubifs_tnc_remove_ino(struct ubifs_in
 		dbg_tnc("xent '%s', ino %lu", xent->name,
 			(unsigned long)xattr_inum);
 
+#ifdef CONFIG_UBIFS_FS_XATTR
+		ubifs_evict_xattr_inode(c, xattr_inum);
+#endif
+
 		nm.name = xent->name;
 		nm.len = le16_to_cpu(xent->nlen);
 		err = ubifs_tnc_remove_nm(c, &key1, &nm);
--- a/fs/ubifs/ubifs.h
+++ b/fs/ubifs/ubifs.h
@@ -1748,6 +1748,7 @@ ssize_t ubifs_getxattr(struct dentry *de
 		       size_t size);
 ssize_t ubifs_listxattr(struct dentry *dentry, char *buffer, size_t size);
 int ubifs_removexattr(struct dentry *dentry, const char *name);
+void ubifs_evict_xattr_inode(struct ubifs_info *c, ino_t xattr_inum);
 
 /* super.c */
 struct inode *ubifs_iget(struct super_block *sb, unsigned long inum);
--- a/fs/ubifs/xattr.c
+++ b/fs/ubifs/xattr.c
@@ -483,6 +483,28 @@ ssize_t ubifs_listxattr(struct dentry *d
 	return written;
 }
 
+/**
+ * ubifs_evict_xattr_inode - Evict an xattr inode.
+ * @c: UBIFS file-system description object
+ * @xattr_inum: xattr inode number
+ *
+ * When an inode that hosts xattrs is being removed we have to make sure
+ * that cached inodes of the xattrs also get removed from the inode cache
+ * otherwise we'd waste memory. This function looks up an inode from the
+ * inode cache and clears the link counter such that iput() will evict
+ * the inode.
+ */
+void ubifs_evict_xattr_inode(struct ubifs_info *c, ino_t xattr_inum)
+{
+	struct inode *inode;
+
+	inode = ilookup(c->vfs_sb, xattr_inum);
+	if (inode) {
+		clear_nlink(inode);
+		iput(inode);
+	}
+}
+
 static int remove_xattr(struct ubifs_info *c, struct inode *host,
 			struct inode *inode, const struct qstr *nm)
 {