Re: [syzbot] [netfs?] INFO: task hung in netfs_unbuffered_write_iter

[Oleg Nesterov <oleg@xxxxxxxxxx>]

On 03/26, Oleg Nesterov wrote:
>
> Hmm... I don't understand why the 2nd vfs_poll(ts->wr) depends on the
> ret from vfs_poll(ts->rd), but I assume this is correct.

I meant, if pt != NULL and ts->rd != ts->wr we need both
vfs_poll(ts->rd) and vfs_poll(ts->wr) ?

and the reproducer writes to the pipe before it mounts 9p...

Prateek, this is just a shot in the dark but since you can reproduce,
can you check if the patch below makes any difference?

Oleg.

--- x/net/9p/trans_fd.c
+++ x/net/9p/trans_fd.c
@@ -234,8 +234,10 @@ p9_fd_poll(struct p9_client *client, str
 	}
 
 	ret = vfs_poll(ts->rd, pt);
-	if (ts->rd != ts->wr)
+	if (ts->rd != ts->wr) {
+		if (pt != NULL) vfs_poll(ts->wr, pt);
 		ret = (ret & ~EPOLLOUT) | (vfs_poll(ts->wr, pt) & ~EPOLLIN);
+	}
 	return ret;
 }