linux-kernel - Re: [LKP] [sunrpc] 6a7da2a288: kernel_BUG_at_lib/iov

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Date:   Fri, 02 Nov 2018 00:50:12 +0000
From:   David Howells <dhowells@...hat.com>
To:     kernel test robot <rong.a.chen@...el.com>
Cc:     dhowells@...hat.com, Leonard Crestez <leonard.crestez@....com>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Jeff Layton <jlayton@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-next@...r.kernel.org" <linux-next@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        lkp@...org
Subject: Re: [LKP] [sunrpc] 6a7da2a288: kernel_BUG_at_lib/iov_iter.c

kernel test robot <rong.a.chen@...el.com> wrote:

> FYI, we noticed the following commit (built with gcc-7):
> 
> commit: 6a7da2a288ce412d7ac117a2912a7b0d9104ee6d ("[RFC] sunrpc: Fix flood of warnings from iov_iter_kvec in linux-next")
> url: https://github.com/0day-ci/linux/commits/Leonard-Crestez/sunrpc-Fix-flood-of-warnings-from-iov_iter_kvec-in-linux-next/20181101-070713
> base: git://git.linux-nfs.org/projects/trondmy/linux-nfs.git linux-next
> 
> in testcase: boot
> 
> on test machine: qemu-system-x86_64 -enable-kvm -cpu kvm64,+ssse3 -smp 2 -m 8G
> 
> caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):

Ummm...  You can't just apply that commit to Trond's linux-next branch unless
that branch also includes the iov_iter changes from my afs-next branch.

Before those changes, ITER_KVEC is required:

	BUG_ON(!(direction & ITER_KVEC));

and after, it will be prohibited:

	WARN_ON(direction & ~(READ | WRITE));

The reason for this is that have yet more patches that split the direction
from the iov_iter::type member into their own member and turn the types into a
simple integer sequence instead of a bit mask.

David