1 files changed, 59 insertions, 19 deletions

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index e8f3170946f..ca6fc0e96d7 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -26,7 +26,7 @@ static inline struct fuse_conn *fuse_get_conn(struct file *file)
 	struct fuse_conn *fc;
 	spin_lock(&fuse_lock);
 	fc = file->private_data;
-	if (fc && !fc->sb)
+	if (fc && !fc->mounted)
 		fc = NULL;
 	spin_unlock(&fuse_lock);
 	return fc;
@@ -148,6 +148,17 @@ void fuse_put_request(struct fuse_conn *fc, struct fuse_req *req)
 		fuse_putback_request(fc, req);
 }
 
+void fuse_release_background(struct fuse_req *req)
+{
+	iput(req->inode);
+	iput(req->inode2);
+	if (req->file)
+		fput(req->file);
+	spin_lock(&fuse_lock);
+	list_del(&req->bg_entry);
+	spin_unlock(&fuse_lock);
+}
+
 /*
  * This function is called when a request is finished.  Either a reply
  * has arrived or it was interrupted (and not yet sent) or some error
@@ -166,12 +177,10 @@ static void request_end(struct fuse_conn *fc, struct fuse_req *req)
 	putback = atomic_dec_and_test(&req->count);
 	spin_unlock(&fuse_lock);
 	if (req->background) {
-		if (req->inode)
-			iput(req->inode);
-		if (req->inode2)
-			iput(req->inode2);
-		if (req->file)
-			fput(req->file);
+		down_read(&fc->sbput_sem);
+		if (fc->mounted)
+			fuse_release_background(req);
+		up_read(&fc->sbput_sem);
 	}
 	wake_up(&req->waitq);
 	if (req->in.h.opcode == FUSE_INIT) {
@@ -191,11 +200,39 @@ static void request_end(struct fuse_conn *fc, struct fuse_req *req)
 		fuse_putback_request(fc, req);
 }
 
-static void background_request(struct fuse_req *req)
+/*
+ * Unfortunately request interruption not just solves the deadlock
+ * problem, it causes problems too.  These stem from the fact, that an
+ * interrupted request is continued to be processed in userspace,
+ * while all the locks and object references (inode and file) held
+ * during the operation are released.
+ *
+ * To release the locks is exactly why there's a need to interrupt the
+ * request, so there's not a lot that can be done about this, except
+ * introduce additional locking in userspace.
+ *
+ * More important is to keep inode and file references until userspace
+ * has replied, otherwise FORGET and RELEASE could be sent while the
+ * inode/file is still used by the filesystem.
+ *
+ * For this reason the concept of "background" request is introduced.
+ * An interrupted request is backgrounded if it has been already sent
+ * to userspace.  Backgrounding involves getting an extra reference to
+ * inode(s) or file used in the request, and adding the request to
+ * fc->background list.  When a reply is received for a background
+ * request, the object references are released, and the request is
+ * removed from the list.  If the filesystem is unmounted while there
+ * are still background requests, the list is walked and references
+ * are released as if a reply was received.
+ *
+ * There's one more use for a background request.  The RELEASE message is
+ * always sent as background, since it doesn't return an error or
+ * data.
+ */
+static void background_request(struct fuse_conn *fc, struct fuse_req *req)
 {
-	/* Need to get hold of the inode(s) and/or file used in the
-	   request, so FORGET and RELEASE are not sent too early */
 	req->background = 1;
+	list_add(&req->bg_entry, &fc->background);
 	if (req->inode)
 		req->inode = igrab(req->inode);
 	if (req->inode2)
@@ -215,7 +252,8 @@ static int request_wait_answer_nonint(struct fuse_req *req)
 }
 
 /* Called with fuse_lock held.  Releases, and then reacquires it. */
-static void request_wait_answer(struct fuse_req *req, int interruptible)
+static void request_wait_answer(struct fuse_conn *fc, struct fuse_req *req,
+				int interruptible)
 {
 	int intr;
 
@@ -255,7 +293,7 @@ static void request_wait_answer(struct fuse_req *req, int interruptible)
 		list_del(&req->list);
 		__fuse_put_request(req);
 	} else if (!req->finished && req->sent)
-		background_request(req);
+		background_request(fc, req);
 }
 
 static unsigned len_args(unsigned numargs, struct fuse_arg *args)
@@ -297,7 +335,7 @@ static void request_send_wait(struct fuse_conn *fc, struct fuse_req *req,
 {
 	req->isreply = 1;
 	spin_lock(&fuse_lock);
-	if (!fc->file)
+	if (!fc->connected)
 		req->out.h.error = -ENOTCONN;
 	else if (fc->conn_error)
 		req->out.h.error = -ECONNREFUSED;
@@ -307,7 +345,7 @@ static void request_send_wait(struct fuse_conn *fc, struct fuse_req *req,
 		   after request_end() */
 		__fuse_get_request(req);
 
-		request_wait_answer(req, interruptible);
+		request_wait_answer(fc, req, interruptible);
 	}
 	spin_unlock(&fuse_lock);
 }
@@ -330,7 +368,7 @@ void request_send_nonint(struct fuse_conn *fc, struct fuse_req *req)
 static void request_send_nowait(struct fuse_conn *fc, struct fuse_req *req)
 {
 	spin_lock(&fuse_lock);
-	if (fc->file) {
+	if (fc->connected) {
 		queue_request(fc, req);
 		spin_unlock(&fuse_lock);
 	} else {
@@ -348,7 +386,9 @@ void request_send_noreply(struct fuse_conn *fc, struct fuse_req *req)
 void request_send_background(struct fuse_conn *fc, struct fuse_req *req)
 {
 	req->isreply = 1;
-	background_request(req);
+	spin_lock(&fuse_lock);
+	background_request(fc, req);
+	spin_unlock(&fuse_lock);
 	request_send_nowait(fc, req);
 }
 
@@ -583,7 +623,7 @@ static void request_wait(struct fuse_conn *fc)
 	DECLARE_WAITQUEUE(wait, current);
 
 	add_wait_queue_exclusive(&fc->waitq, &wait);
-	while (fc->sb && list_empty(&fc->pending)) {
+	while (fc->mounted && list_empty(&fc->pending)) {
 		set_current_state(TASK_INTERRUPTIBLE);
 		if (signal_pending(current))
 			break;
@@ -622,7 +662,7 @@ static ssize_t fuse_dev_readv(struct file *file, const struct iovec *iov,
 		goto err_unlock;
 	request_wait(fc);
 	err = -ENODEV;
-	if (!fc->sb)
+	if (!fc->mounted)
 		goto err_unlock;
 	err = -ERESTARTSYS;
 	if (list_empty(&fc->pending))
@@ -839,7 +879,7 @@ static int fuse_dev_release(struct inode *inode, struct file *file)
 	spin_lock(&fuse_lock);
 	fc = file->private_data;
 	if (fc) {
-		fc->file = NULL;
+		fc->connected = 0;
 		end_requests(fc, &fc->pending);
 		end_requests(fc, &fc->processing);
 		fuse_release_conn(fc);