Re: [syzbot] [netfs?] WARNING: refcount bug in netfs_put_subrequest

[Hillf Danton <hdanton@sina.com>]

On Thu, 13 Feb 2025 22:39:25 -0800
> syzbot found the following issue on:
> 
> HEAD commit:    69b54314c975 Merge tag 'kbuild-fixes-v6.14' of git://git.k..
> git tree:       upstream
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13aafdf8580000

#syz test upstream   master

--- x/fs/netfs/read_collect.c
+++ y/fs/netfs/read_collect.c
@@ -289,6 +289,10 @@ reassess:
 		/* Remove if completely consumed. */
 		stream->source = front->source;
 		spin_lock(&rreq->lock);
+		if (front != stream->front) {
+			spin_unlock(&rreq->lock);
+			goto reassess;
+		}
 
 		remove = front;
 		trace_netfs_sreq(front, netfs_sreq_trace_discard);
@@ -345,6 +349,7 @@ static void netfs_rreq_assess_dio(struct
 	struct netfs_io_subrequest *subreq;
 	struct netfs_io_stream *stream = &rreq->io_streams[0];
 	unsigned int i;
+	struct kiocb *iocb = NULL;
 
 	/* Collect unbuffered reads and direct reads, adding up the transfer
 	 * sizes until we find the first short or failed subrequest.
@@ -369,12 +374,16 @@ static void netfs_rreq_assess_dio(struct
 		}
 	}
 
+	spin_lock(&rreq->lock);
 	if (rreq->iocb) {
 		rreq->iocb->ki_pos += rreq->transferred;
 		if (rreq->iocb->ki_complete)
-			rreq->iocb->ki_complete(
-				rreq->iocb, rreq->error ? rreq->error : rreq->transferred);
+			iocb = rreq->iocb;
+		rreq->iocb = NULL;
 	}
+	spin_unlock(&rreq->lock);
+	if (iocb)
+		iocb->ki_complete(iocb, rreq->error ? rreq->error : rreq->transferred);
 	if (rreq->netfs_ops->done)
 		rreq->netfs_ops->done(rreq);
 	if (rreq->origin == NETFS_DIO_READ)
--