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    SubjectRe: [PATCH v3 1/7] mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case
    On 03/09/20 at 09:58am, David Hildenbrand wrote:
    > On 07.03.20 09:42, Baoquan He 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.
    > >
    > > Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug")
    > > Signed-off-by: Baoquan He <bhe@redhat.com>
    > > Cc: stable@vger.kernel.org
    > > ---
    > > mm/sparse.c | 8 ++++++--
    > > 1 file changed, 6 insertions(+), 2 deletions(-)
    > >
    > > diff --git a/mm/sparse.c b/mm/sparse.c
    > > index 42c18a38ffaa..1b50c15677d7 100644
    > > --- a/mm/sparse.c
    > > +++ b/mm/sparse.c
    > > @@ -734,6 +734,7 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
    > > struct mem_section *ms = __pfn_to_section(pfn);
    > > bool section_is_early = early_section(ms);
    > > struct page *memmap = NULL;
    > > + bool empty = false;
    >
    > Oh, one NIT: no need to initialize empty to false.

    Thanks for careful reviewing, David.

    Not very sure about this, do you have a doc or discussion thread about
    not initializing local variable? Maybe Andrew can help update it if this
    is not suggested.

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