linux-kernel - Re: dev_pagemap related cleanups

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Date:   Thu, 13 Jun 2019 11:27:39 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Jérôme Glisse <jglisse@...hat.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Ben Skeggs <bskeggs@...hat.com>, Linux MM <linux-mm@...ck.org>,
        nouveau@...ts.freedesktop.org,
        Maling list - DRI developers 
        <dri-devel@...ts.freedesktop.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        linux-pci@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: dev_pagemap related cleanups

On Thu, Jun 13, 2019 at 2:43 AM Christoph Hellwig <hch@....de> wrote:
>
> Hi Dan, Jérôme and Jason,
>
> below is a series that cleans up the dev_pagemap interface so that
> it is more easily usable, which removes the need to wrap it in hmm
> and thus allowing to kill a lot of code
>
> Diffstat:
>
>  22 files changed, 245 insertions(+), 802 deletions(-)

Hooray!

> Git tree:
>
>     git://git.infradead.org/users/hch/misc.git hmm-devmem-cleanup

I just realized this collides with the dev_pagemap release rework in
Andrew's tree (commit ids below are from next.git and are not stable)

4422ee8476f0 mm/devm_memremap_pages: fix final page put race
771f0714d0dc PCI/P2PDMA: track pgmap references per resource, not globally
af37085de906 lib/genalloc: introduce chunk owners
e0047ff8aa77 PCI/P2PDMA: fix the gen_pool_add_virt() failure path
0315d47d6ae9 mm/devm_memremap_pages: introduce devm_memunmap_pages
216475c7eaa8 drivers/base/devres: introduce devm_release_action()

CONFLICT (content): Merge conflict in tools/testing/nvdimm/test/iomap.c
CONFLICT (content): Merge conflict in mm/hmm.c
CONFLICT (content): Merge conflict in kernel/memremap.c
CONFLICT (content): Merge conflict in include/linux/memremap.h
CONFLICT (content): Merge conflict in drivers/pci/p2pdma.c
CONFLICT (content): Merge conflict in drivers/nvdimm/pmem.c
CONFLICT (content): Merge conflict in drivers/dax/device.c
CONFLICT (content): Merge conflict in drivers/dax/dax-private.h

Perhaps we should pull those out and resend them through hmm.git?

It also turns out the nvdimm unit tests crash with this signature on
that branch where base v5.2-rc3 passes:

    BUG: kernel NULL pointer dereference, address: 0000000000000008
    [..]
    CPU: 15 PID: 1414 Comm: lt-libndctl Tainted: G           OE
5.2.0-rc3+ #3399
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015
    RIP: 0010:percpu_ref_kill_and_confirm+0x1e/0x180
    [..]
    Call Trace:
     release_nodes+0x234/0x280
     device_release_driver_internal+0xe8/0x1b0
     bus_remove_device+0xf2/0x160
     device_del+0x166/0x370
     unregister_dev_dax+0x23/0x50
     release_nodes+0x234/0x280
     device_release_driver_internal+0xe8/0x1b0
     unbind_store+0x94/0x120
     kernfs_fop_write+0xf0/0x1a0
     vfs_write+0xb7/0x1b0
     ksys_write+0x5c/0xd0
     do_syscall_64+0x60/0x240

The crash bisects to:

    d8cc8bbe108c device-dax: use the dev_pagemap internal refcount