Re: [PATCH v3 1/7] mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case

[Pankaj Gupta]

>
> 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@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> ---
>  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;
>         unsigned long *subsection_map = ms->usage
>                 ? &ms->usage->subsection_map[0] : NULL;
>
> @@ -764,7 +765,8 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
>          * For 2/ and 3/ the SPARSEMEM_VMEMMAP={y,n} cases are unified
>          */
>         bitmap_xor(subsection_map, map, subsection_map, SUBSECTIONS_PER_SECTION);
> -       if (bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION)) {
> +       empty = bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION);
> +       if (empty) {
>                 unsigned long section_nr = pfn_to_section_nr(pfn);
>
>                 /*
> @@ -779,13 +781,15 @@ 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 (empty)
> +               ms->section_mem_map = (unsigned long)NULL;
>  }
>
>  static struct page * __meminit section_activate(int nid, unsigned long pfn,
> --

Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@xxxxxxxxx>

> 2.17.2
>
>