On 09.03.20 14:18, Baoquan He wrote:
> 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@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;
>>
>> 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.
The general rule is to no initialize what will always be initialized
later. Compare with most other code in-tree - e.g., sparse_init_nid.
Makes the code usually easier to follow.
--
Thanks,
David / dhildenb
