fuse: serialize dirops by default

Negotiate with userspace filesystems whether they support parallel readdir
and lookup.  Disable parallelism by default for fear of breaking fuse
filesystems.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Fixes: 9902af79 ("parallel lookups: actual switch to rwsem")
Fixes: d9b3dbdc ("fuse: switch to ->iterate_shared()")

fs/fuse/dir.c

@@ -341,8 +341,10 @@ static struct dentry *fuse_lookup(struct inode *dir, struct dentry *entry,
 	struct dentry *newent;
 	bool outarg_valid = true;
 
+	fuse_lock_inode(dir);
 	err = fuse_lookup_name(dir->i_sb, get_node_id(dir), &entry->d_name,
 			       &outarg, &inode);
+	fuse_unlock_inode(dir);
 	if (err == -ENOENT) {
 		outarg_valid = false;
 		err = 0;
@@ -1341,7 +1343,9 @@ static int fuse_readdir(struct file *file, struct dir_context *ctx)
 		fuse_read_fill(req, file, ctx->pos, PAGE_SIZE,
 			       FUSE_READDIR);
 	}
+	fuse_lock_inode(inode);
 	fuse_request_send(fc, req);
+	fuse_unlock_inode(inode);
 	nbytes = req->out.args[0].size;
 	err = req->out.h.error;
 	fuse_put_request(fc, req);

fs/fuse/fuse_i.h

@@ -110,6 +110,9 @@ struct fuse_inode {
 
 	/** Miscellaneous bits describing inode state */
 	unsigned long state;
+
+	/** Lock for serializing lookup and readdir for back compatibility*/
+	struct mutex mutex;
 };
 
 /** FUSE inode state bits */
@@ -540,6 +543,9 @@ struct fuse_conn {
 	/** write-back cache policy (default is write-through) */
 	unsigned writeback_cache:1;
 
+	/** allow parallel lookups and readdir (default is serialized) */
+	unsigned parallel_dirops:1;
+
 	/*
 	 * The following bitfields are only for optimization purposes
 	 * and hence races in setting them will not cause malfunction
@@ -956,4 +962,7 @@ int fuse_do_setattr(struct inode *inode, struct iattr *attr,
 
 void fuse_set_initialized(struct fuse_conn *fc);
 
+void fuse_unlock_inode(struct inode *inode);
+void fuse_lock_inode(struct inode *inode);
+
 #endif /* _FS_FUSE_I_H */

fs/fuse/inode.c

@@ -97,6 +97,7 @@ static struct inode *fuse_alloc_inode(struct super_block *sb)
 	INIT_LIST_HEAD(&fi->queued_writes);
 	INIT_LIST_HEAD(&fi->writepages);
 	init_waitqueue_head(&fi->page_waitq);
+	mutex_init(&fi->mutex);
 	fi->forget = fuse_alloc_forget();
 	if (!fi->forget) {
 		kmem_cache_free(fuse_inode_cachep, inode);
@@ -117,6 +118,7 @@ static void fuse_destroy_inode(struct inode *inode)
 	struct fuse_inode *fi = get_fuse_inode(inode);
 	BUG_ON(!list_empty(&fi->write_files));
 	BUG_ON(!list_empty(&fi->queued_writes));
+	mutex_destroy(&fi->mutex);
 	kfree(fi->forget);
 	call_rcu(&inode->i_rcu, fuse_i_callback);
 }
@@ -351,6 +353,18 @@ int fuse_reverse_inval_inode(struct super_block *sb, u64 nodeid,
 	return 0;
 }
 
+void fuse_lock_inode(struct inode *inode)
+{
+	if (!get_fuse_conn(inode)->parallel_dirops)
+		mutex_lock(&get_fuse_inode(inode)->mutex);
+}
+
+void fuse_unlock_inode(struct inode *inode)
+{
+	if (!get_fuse_conn(inode)->parallel_dirops)
+		mutex_unlock(&get_fuse_inode(inode)->mutex);
+}
+
 static void fuse_umount_begin(struct super_block *sb)
 {
 	fuse_abort_conn(get_fuse_conn_super(sb));
@@ -898,6 +912,8 @@ static void process_init_reply(struct fuse_conn *fc, struct fuse_req *req)
 				fc->async_dio = 1;
 			if (arg->flags & FUSE_WRITEBACK_CACHE)
 				fc->writeback_cache = 1;
+			if (arg->flags & FUSE_PARALLEL_DIROPS)
+				fc->parallel_dirops = 1;
 			if (arg->time_gran && arg->time_gran <= 1000000000)
 				fc->sb->s_time_gran = arg->time_gran;
 		} else {
@@ -928,7 +944,8 @@ static void fuse_send_init(struct fuse_conn *fc, struct fuse_req *req)
 		FUSE_SPLICE_WRITE | FUSE_SPLICE_MOVE | FUSE_SPLICE_READ |
 		FUSE_FLOCK_LOCKS | FUSE_IOCTL_DIR | FUSE_AUTO_INVAL_DATA |
 		FUSE_DO_READDIRPLUS | FUSE_READDIRPLUS_AUTO | FUSE_ASYNC_DIO |
-		FUSE_WRITEBACK_CACHE | FUSE_NO_OPEN_SUPPORT;
+		FUSE_WRITEBACK_CACHE | FUSE_NO_OPEN_SUPPORT |
+		FUSE_PARALLEL_DIROPS;
 	req->in.h.opcode = FUSE_INIT;
 	req->in.numargs = 1;
 	req->in.args[0].size = sizeof(*arg);

include/uapi/linux/fuse.h

@@ -105,6 +105,9 @@
  *
  *  7.24
  *  - add FUSE_LSEEK for SEEK_HOLE and SEEK_DATA support
+ *
+ *  7.25
+ *  - add FUSE_PARALLEL_DIROPS
  */
 
 #ifndef _LINUX_FUSE_H
@@ -140,7 +143,7 @@
 #define FUSE_KERNEL_VERSION 7
 
 /** Minor version number of this interface */
-#define FUSE_KERNEL_MINOR_VERSION 24
+#define FUSE_KERNEL_MINOR_VERSION 25
 
 /** The node ID of the root inode */
 #define FUSE_ROOT_ID 1
@@ -234,6 +237,7 @@ struct fuse_file_lock {
  * FUSE_ASYNC_DIO: asynchronous direct I/O submission
  * FUSE_WRITEBACK_CACHE: use writeback cache for buffered writes
  * FUSE_NO_OPEN_SUPPORT: kernel supports zero-message opens
+ * FUSE_PARALLEL_DIROPS: allow parallel lookups and readdir
  */
 #define FUSE_ASYNC_READ		(1 << 0)
 #define FUSE_POSIX_LOCKS	(1 << 1)
@@ -253,6 +257,7 @@ struct fuse_file_lock {
 #define FUSE_ASYNC_DIO		(1 << 15)
 #define FUSE_WRITEBACK_CACHE	(1 << 16)
 #define FUSE_NO_OPEN_SUPPORT	(1 << 17)
+#define FUSE_PARALLEL_DIROPS    (1 << 18)
 
 /**
  * CUSE INIT request/reply flags