Re: [syzbot] [netfs?] WARNING in netfs_retry_reads

[Hillf Danton]

On Thu, Nov 28, 2024 at 11:27:24PM -0800, syzbot wrote:
> syzbot found the following issue on:
> 
> HEAD commit:    85a2dd7d7c81 Add linux-next specific files for 20241125
> git tree:       linux-next
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14e3a5c0580000

#syz test

--- x/fs/netfs/read_collect.c
+++ y/fs/netfs/read_collect.c
@@ -619,8 +619,7 @@ ssize_t netfs_wait_for_read(struct netfs
 
 	for (;;) {
 		trace_netfs_rreq(rreq, netfs_rreq_trace_wait_queue);
-		prepare_to_wait(&rreq->waitq, &myself, TASK_UNINTERRUPTIBLE);
-
+		smp_mb();
 		subreq = list_first_entry_or_null(&stream->subrequests,
 						  struct netfs_io_subrequest, rreq_link);
 		if (subreq &&
@@ -628,6 +627,7 @@ ssize_t netfs_wait_for_read(struct netfs
 		     test_bit(NETFS_SREQ_MADE_PROGRESS, &subreq->flags)))
 			netfs_read_collection(rreq);
 
+		prepare_to_wait(&rreq->waitq, &myself, TASK_UNINTERRUPTIBLE);
 		if (!test_bit(NETFS_RREQ_IN_PROGRESS, &rreq->flags))
 			break;
 
--