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

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Message-ID: <20200309125617.GO8447@dhcp22.suse.cz>
Date:   Mon, 9 Mar 2020 13:56:17 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Baoquan He <bhe@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, david@...hat.com,
        richardw.yang@...ux.intel.com, dan.j.williams@...el.com,
        osalvador@...e.de, rppt@...ux.ibm.com
Subject: Re: [PATCH v3 1/7] mm/hotplug: fix hot remove failure in
 SPARSEMEM|!VMEMMAP case

On Sat 07-03-20 16:42:23, 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@...hat.com>
> Cc: stable@...r.kernel.org

Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  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,
> -- 
> 2.17.2
> 

-- 
Michal Hocko
SUSE Labs