linux-kernel - Re: DAX can not work on virtual nvdimm device

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Date:   Fri, 19 Aug 2016 07:59:29 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Xiao Guangrong <guangrong.xiao@...ux.intel.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        "qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
        KVM <kvm@...r.kernel.org>,
        "Zhang, Haozhong" <haozhong.zhang@...el.com>,
        Yumei Huang <yuhuang@...hat.com>
Subject: Re: DAX can not work on virtual nvdimm device

On Fri, Aug 19, 2016 at 4:19 AM, Xiao Guangrong
<guangrong.xiao@...ux.intel.com> wrote:
>
> Hi Dan,
>
> Recently, Redhat reported that nvml test suite failed on QEMU/KVM,
> more detailed info please refer to:
>    https://bugzilla.redhat.com/show_bug.cgi?id=1365721
>
> The reason for this bug is that the memory region created by mmap()
> on the dax-based file was gone so that the region can not be found
> in /proc/self/smaps during the runtime.
>
> This is a simple way to trigger this issue:
>    mount -o dax /dev/pmem0 /mnt/pmem/
>    vim /mnt/pmem/xxx
> then 'vim' is crashed due to segment fault.
>
> This bug can be reproduced on your tree, the top commit is
> 10d7902fa0e82b (dax: unmap/truncate on device shutdown), the kernel
> configure file is attached.
>
> Your thought or comment is highly appreciated.

I'm going to be offline until Tuesday, but I will investigate when I'm
back.  In the meantime if Ross or Vishal had an opportunity to take a
look I wouldn't say "no" :).