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    SubjectRe: [PATCH v2 1/7] mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case
    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>

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