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From:   Dan Williams <dan.j.williams@intel.com>
Date:   Wed, 26 Feb 2020 10:09:15 -0800
Message-ID: <CAPcyv4g9Ywpz=37tjmw_1TAkKEpQ7R--yHoExdrSd4sJ0gqY3A@mail.gmail.com>
Subject: Re: [PATCH v2 1/7] mm/hotplug: fix hot remove failure in
 SPARSEMEM|!VMEMMAP case
To:     Baoquan He <bhe@redhat.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux MM <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Wei Yang <richardw.yang@linux.intel.com>,
        David Hildenbrand <david@redhat.com>,
        Oscar Salvador <osalvador@suse.de>,
        Michal Hocko <mhocko@suse.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Robin Murphy <robin.murphy@arm.com>
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On Wed, Feb 19, 2020 at 8:34 PM Baoquan He <bhe@redhat.com> wrote:
>
> In section_deactivate(), pfn_to_page() doesn't work any more after
> ms->section_mem_map is resetting to NULL in SPARSEMEM|!VMEMMAP case.
> It caused hot remove failure:
>
> kernel BUG at mm/page_alloc.c:4806!
> invalid opcode: 0000 [#1] SMP PTI
> CPU: 3 PID: 8 Comm: kworker/u16:0 Tainted: G        W         5.5.0-next-20200205+ #340
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015
> Workqueue: kacpi_hotplug acpi_hotplug_work_fn
> RIP: 0010:free_pages+0x85/0xa0
> Call Trace:
>  __remove_pages+0x99/0xc0
>  arch_remove_memory+0x23/0x4d
>  try_remove_memory+0xc8/0x130
>  ? walk_memory_blocks+0x72/0xa0
>  __remove_memory+0xa/0x11
>  acpi_memory_device_remove+0x72/0x100
>  acpi_bus_trim+0x55/0x90
>  acpi_device_hotplug+0x2eb/0x3d0
>  acpi_hotplug_work_fn+0x1a/0x30
>  process_one_work+0x1a7/0x370
>  worker_thread+0x30/0x380
>  ? flush_rcu_work+0x30/0x30
>  kthread+0x112/0x130
>  ? kthread_create_on_node+0x60/0x60
>  ret_from_fork+0x35/0x40
>
> Let's move the ->section_mem_map resetting after depopulate_section_memmap()
> to fix it.
>
> Signed-off-by: Baoquan He <bhe@redhat.com>
> ---
>  mm/sparse.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 596b2a45b100..b8e52c8fed7f 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -779,13 +779,15 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
>                         ms->usage = NULL;
>                 }
>                 memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr);
> -               ms->section_mem_map = (unsigned long)NULL;
>         }
>
>         if (section_is_early && memmap)
>                 free_map_bootmem(memmap);
>         else
>                 depopulate_section_memmap(pfn, nr_pages, altmap);
> +
> +       if (bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION))
> +               ms->section_mem_map = (unsigned long)NULL;

Looks good to me:

Reviewed-by: Dan Williams <dan.j.williams@intel.com>