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In-Reply-To: <20180928084433.GB25561@techadventures.net>
From: Dan Williams <dan.j.williams@intel.com>
Date: Fri, 28 Sep 2018 08:50:46 -0700
Message-ID: <CAPcyv4hY97wL53Pa8oaq4UK6OS4R48_35nJhbY4SYmoMSctQHA@mail.gmail.com>
Subject: Re: [PATCH v5 4/4] mm: Defer ZONE_DEVICE page initialization to the
 point where we init pgmap
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Sender: owner-linux-mm@kvack.org
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To: osalvador@techadventures.net
Cc: Michal Hocko <mhocko@kernel.org>, alexander.h.duyck@linux.intel.com, Linux MM <linux-mm@kvack.org>, Andrew Morton <akpm@linux-foundation.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-nvdimm <linux-nvdimm@lists.01.org>, Pasha Tatashin <pavel.tatashin@microsoft.com>, Dave Jiang <dave.jiang@intel.com>, Dave Hansen <dave.hansen@intel.com>, =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>, rppt@linux.vnet.ibm.com, Logan Gunthorpe <logang@deltatee.com>, Ingo Molnar <mingo@kernel.org>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>

On Fri, Sep 28, 2018 at 1:45 AM Oscar Salvador
<osalvador@techadventures.net> wrote:
>
> On Fri, Sep 28, 2018 at 10:12:24AM +0200, Oscar Salvador wrote:
> > Although I am not sure about leaving memmap_init_zone unprotected.
> > For the normal memory, that is not a problem since the memblock's lock
> > protects us from touching the same pages at the same time in online/offline_pages,
> > but for HMM/devm the story is different.
> >
> > I am totally unaware of HMM/devm, so I am not sure if its protected somehow.
> > e.g: what happens if devm_memremap_pages and devm_memremap_pages_release are running
> > at the same time for the same memory-range (with the assumption that the hotplug-lock
> > does not protect move_pfn_range_to_zone anymore).
>
> I guess that this could not happen since the device is not linked to devm_memremap_pages_release
> until the end with:
>
> devm_add_action(dev, devm_memremap_pages_release, pgmap)

It's a bug if devm_memremap_pages and devm_memremap_pages_release are
running simultaneously for the same range. This is enforced by the
requirement that the caller has done a successful request_region() on
the range before the call to map pages.