fuse: fix double request_end()

BugLink: https://bugs.launchpad.net/bugs/1792392

commit 87114373 upstream.

Refcounting of request is broken when fuse_abort_conn() is called and
request is on the fpq->io list:

 - ref is taken too late
 - then it is not dropped

Fixes: 0d8e84b0 ("fuse: simplify request abort")
Cc: <stable@vger.kernel.org> # v4.2
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

fs/fuse/dev.c

@@ -387,7 +387,7 @@ static void request_end(struct fuse_conn *fc, struct fuse_req *req)
 	struct fuse_iqueue *fiq = &fc->iq;
 
 	if (test_and_set_bit(FR_FINISHED, &req->flags))
-		return;
+		goto out_put_req;
 
 	spin_lock(&fiq->waitq.lock);
 	list_del_init(&req->intr_entry);
@@ -417,6 +417,7 @@ static void request_end(struct fuse_conn *fc, struct fuse_req *req)
 	wake_up(&req->waitq);
 	if (req->end)
 		req->end(fc, req);
+out_put_req:
 	fuse_put_request(fc, req);
 }
 
@@ -2167,6 +2168,7 @@ void fuse_abort_conn(struct fuse_conn *fc)
 				set_bit(FR_ABORTED, &req->flags);
 				if (!test_bit(FR_LOCKED, &req->flags)) {
 					set_bit(FR_PRIVATE, &req->flags);
+					__fuse_get_request(req);
 					list_move(&req->list, &to_end1);
 				}
 				spin_unlock(&req->waitq.lock);
@@ -2193,7 +2195,6 @@ void fuse_abort_conn(struct fuse_conn *fc)
 
 		while (!list_empty(&to_end1)) {
 			req = list_first_entry(&to_end1, struct fuse_req, list);
-			__fuse_get_request(req);
 			list_del_init(&req->list);
 			request_end(fc, req);
 		}