linux-kernel - Re: [PATCH v2 1/7] mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case

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Date:   Wed, 26 Feb 2020 13:31:53 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Baoquan He <bhe@...hat.com>, linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        richardw.yang@...ux.intel.com, osalvador@...e.de,
        dan.j.williams@...el.com, mhocko@...e.com, rppt@...ux.ibm.com,
        robin.murphy@....com
Subject: Re: [PATCH v2 1/7] mm/hotplug: fix hot remove failure in
 SPARSEMEM|!VMEMMAP case

On 20.02.20 05:33, 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: Tag? Stable: Tag?

> Signed-off-by: Baoquan He <bhe@...hat.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;
>  }
>  
>  static struct page * __meminit section_activate(int nid, unsigned long pfn,
> 

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb