Merge tag '9p-for-5.19-rc4' of https://github.com/martinetd/linux

Pull 9pfs fixes from Dominique Martinet:
 "A couple of fid refcount and fscache fixes:

   - fid refcounting was incorrect in some corner cases and would leak
     resources, only freed at umount time. The first three commits fix
     three such cases

   - 'cache=loose' or fscache was broken when trying to write a partial
     page to a file with no read permission since the rework a few
     releases ago.

     The fix taken here is just to restore old behavior of using the
     special 'writeback_fid' for such reads, which is open as root/RDWR
     and such not get complains that we try to read on a WRONLY fid.

     Long-term it'd be nice to get rid of this and not issue the read at
     all (skip cache?) in such cases, but that direction hasn't
     progressed"

* tag '9p-for-5.19-rc4' of https://github.com/martinetd/linux:
  9p: fix EBADF errors in cached mode
  9p: Fix refcounting during full path walks for fid lookups
  9p: fix fid refcount leak in v9fs_vfs_get_link
  9p: fix fid refcount leak in v9fs_vfs_atomic_open_dotl

fs/9p/fid.c

@@ -152,7 +152,7 @@ static struct p9_fid *v9fs_fid_lookup_with_uid(struct dentry *dentry,
 	const unsigned char **wnames, *uname;
 	int i, n, l, clone, access;
 	struct v9fs_session_info *v9ses;
-	struct p9_fid *fid, *old_fid = NULL;
+	struct p9_fid *fid, *old_fid;
 
 	v9ses = v9fs_dentry2v9ses(dentry);
 	access = v9ses->flags & V9FS_ACCESS_MASK;
@@ -194,13 +194,12 @@ static struct p9_fid *v9fs_fid_lookup_with_uid(struct dentry *dentry,
 		if (IS_ERR(fid))
 			return fid;
 
+		refcount_inc(&fid->count);
 		v9fs_fid_add(dentry->d_sb->s_root, fid);
 	}
 	/* If we are root ourself just return that */
-	if (dentry->d_sb->s_root == dentry) {
-		refcount_inc(&fid->count);
+	if (dentry->d_sb->s_root == dentry)
 		return fid;
-	}
 	/*
 	 * Do a multipath walk with attached root.
 	 * When walking parent we need to make sure we
@@ -212,6 +211,7 @@ static struct p9_fid *v9fs_fid_lookup_with_uid(struct dentry *dentry,
 		fid = ERR_PTR(n);
 		goto err_out;
 	}
+	old_fid = fid;
 	clone = 1;
 	i = 0;
 	while (i < n) {
@@ -221,19 +221,15 @@ static struct p9_fid *v9fs_fid_lookup_with_uid(struct dentry *dentry,
 		 * walk to ensure none of the patch component change
 		 */
 		fid = p9_client_walk(fid, l, &wnames[i], clone);
+		/* non-cloning walk will return the same fid */
+		if (fid != old_fid) {
+			p9_client_clunk(old_fid);
+			old_fid = fid;
+		}
 		if (IS_ERR(fid)) {
-			if (old_fid) {
-				/*
-				 * If we fail, clunk fid which are mapping
-				 * to path component and not the last component
-				 * of the path.
-				 */
-				p9_client_clunk(old_fid);
-			}
 			kfree(wnames);
 			goto err_out;
 		}
-		old_fid = fid;
 		i += l;
 		clone = 0;
 	}

fs/9p/vfs_addr.c

@@ -58,8 +58,21 @@ static void v9fs_issue_read(struct netfs_io_subrequest *subreq)
  */
 static int v9fs_init_request(struct netfs_io_request *rreq, struct file *file)
 {
+	struct inode *inode = file_inode(file);
+	struct v9fs_inode *v9inode = V9FS_I(inode);
 	struct p9_fid *fid = file->private_data;
 
+	BUG_ON(!fid);
+
+	/* we might need to read from a fid that was opened write-only
+	 * for read-modify-write of page cache, use the writeback fid
+	 * for that */
+	if (rreq->origin == NETFS_READ_FOR_WRITE &&
+			(fid->mode & O_ACCMODE) == O_WRONLY) {
+		fid = v9inode->writeback_fid;
+		BUG_ON(!fid);
+	}
+
 	refcount_inc(&fid->count);
 	rreq->netfs_priv = fid;
 	return 0;

fs/9p/vfs_inode.c

@@ -1251,15 +1251,15 @@ static const char *v9fs_vfs_get_link(struct dentry *dentry,
 		return ERR_PTR(-ECHILD);
 
 	v9ses = v9fs_dentry2v9ses(dentry);
-	fid = v9fs_fid_lookup(dentry);
+	if (!v9fs_proto_dotu(v9ses))
+		return ERR_PTR(-EBADF);
+
 	p9_debug(P9_DEBUG_VFS, "%pd\n", dentry);
+	fid = v9fs_fid_lookup(dentry);
 
 	if (IS_ERR(fid))
 		return ERR_CAST(fid);
 
-	if (!v9fs_proto_dotu(v9ses))
-		return ERR_PTR(-EBADF);
-
 	st = p9_client_stat(fid);
 	p9_client_clunk(fid);
 	if (IS_ERR(st))

fs/9p/vfs_inode_dotl.c

@@ -274,6 +274,7 @@ v9fs_vfs_atomic_open_dotl(struct inode *dir, struct dentry *dentry,
 	if (IS_ERR(ofid)) {
 		err = PTR_ERR(ofid);
 		p9_debug(P9_DEBUG_VFS, "p9_client_walk failed %d\n", err);
+		p9_client_clunk(dfid);
 		goto out;
 	}
 
@@ -285,13 +286,15 @@ v9fs_vfs_atomic_open_dotl(struct inode *dir, struct dentry *dentry,
 	if (err) {
 		p9_debug(P9_DEBUG_VFS, "Failed to get acl values in creat %d\n",
 			 err);
+		p9_client_clunk(dfid);
 		goto error;
 	}
 	err = p9_client_create_dotl(ofid, name, v9fs_open_to_dotl_flags(flags),
 				    mode, gid, &qid);
 	if (err < 0) {
 		p9_debug(P9_DEBUG_VFS, "p9_client_open_dotl failed in creat %d\n",
 			 err);
+		p9_client_clunk(dfid);
 		goto error;
 	}
 	v9fs_invalidate_inode_attr(dir);