linux-kernel - Re: [PATCH 5/5] dax: "Hotplug" persistent memory for use like normal RAM

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Date:   Tue, 12 Feb 2019 16:30:17 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Brice Goglin <Brice.Goglin@...ia.fr>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Michal Hocko <mhocko@...e.com>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Takashi Iwai <tiwai@...e.de>,
        Ross Zwisler <zwisler@...nel.org>,
        Linux MM <linux-mm@...ck.org>,
        Jérôme Glisse <jglisse@...hat.com>,
        Fengguang Wu <fengguang.wu@...el.com>,
        Yaowei Bai <baiyaowei@...s.chinamobile.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH 5/5] dax: "Hotplug" persistent memory for use like normal RAM

On Tue, Feb 12, 2019 at 11:59 AM Brice Goglin <Brice.Goglin@...ia.fr> wrote:
>
> Le 11/02/2019 à 17:22, Dave Hansen a écrit :
>
> > On 2/9/19 3:00 AM, Brice Goglin wrote:
> >> I've used your patches on fake hardware (memmap=xx!yy) with an older
> >> nvdimm-pending branch (without Keith's patches). It worked fine. This
> >> time I am running on real Intel hardware. Any idea where to look ?
> > I've run them on real Intel hardware too.
> >
> > Could you share the exact sequence of commands you're issuing to
> > reproduce the hang?  My guess would be that there's some odd interaction
> > between Dan's latest branch and my now (slightly) stale patches.
> >
> > I'll refresh them this week and see if I can reproduce what you're seeing.
>
> # ndctl disable-region all
> # ndctl zero-labels all
> # ndctl enable-region region0
> # ndctl create-namespace -r region0 -t pmem -m devdax
> {
>   "dev":"namespace0.0",
>   "mode":"devdax",
>   "map":"dev",
>   "size":"1488.37 GiB (1598.13 GB)",
>   "uuid":"ad0096d7-3fe7-4402-b529-ad64ed0bf789",
>   "daxregion":{
>     "id":0,
>     "size":"1488.37 GiB (1598.13 GB)",
>     "align":2097152,
>     "devices":[
>       {
>         "chardev":"dax0.0",
>         "size":"1488.37 GiB (1598.13 GB)"
>       }
>     ]
>   },
>   "align":2097152
> }
> # ndctl enable-namespace namespace0.0
> # echo -n dax0.0 > /sys/bus/dax/drivers/device_dax/remove_id
> <hang>
>
> I tried with and without dax_pmem_compat loaded, but it doesn't help.

I think this is due to:

  a9f1ffdb6a20 device-dax: Auto-bind device after successful new_id

I missed that this path is also called in the remove_id path. Thanks
for the bug report! I'll get this fixed up.