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

[Baoquan He]

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.