linux-kernel - Re: [-next] strace tests fail because of "y2038: socket: Add compat_sys_recvmmsg

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Date:   Mon, 17 Dec 2018 23:05:06 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Heiko Carstens <heiko.carstens@...ibm.com>
Cc:     Linux-Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [-next] strace tests fail because of "y2038: socket: Add compat_sys_recvmmsg_time64"

On Mon, Dec 17, 2018 at 10:40 PM Arnd Bergmann <arnd@...db.de> wrote:
>
> On Mon, Dec 17, 2018 at 2:06 PM Heiko Carstens
> <heiko.carstens@...ibm.com> wrote:
> >
> > Hi Arnd,
> >
> > in linux-next as of today 16 strace self tests fail on s390. I could
> > bisect this to b136972b063b ("y2038: socket: Add compat_sys_recvmmsg_time64").
> >
> > The following tests fail:
>
> Hi Heiko,
>
> Thanks for the report and sorry I broke things. I'll have a closer look
> tomorrow if I don't find it right away. I suppose the regression was in
> native system calls, not the compat syscalls with 31-bit user space,
> right?

I found a bug in my patch by inspection. Can you try if the patch
below makes it all work (apologies for the garbled whitespace),
I'm considering a rewrite of that function now (to split it into two
again), but want to make sure there isn't another problem in my
original patch.

     Arnd

----
diff --git a/net/socket.c b/net/socket.c
index 3bb2ee083f97..7f9f225d0b6c 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2486,12 +2486,12 @@ int __sys_recvmmsg(int fd, struct mmsghdr __user *mmsg,
         return -EFAULT;

     if (!timeout && !timeout32)
-        do_recvmmsg(fd, mmsg, vlen, flags, NULL);
+        return do_recvmmsg(fd, mmsg, vlen, flags, NULL);

     datagrams = do_recvmmsg(fd, mmsg, vlen, flags, &timeout_sys);

-    if (!datagrams)
-        return 0;
+    if (datagrams <= 0)
+        return datagrams;

     if (timeout && put_timespec64(&timeout_sys, timeout))
         datagrams = -EFAULT;