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Date:   Thu, 20 Feb 2020 14:11:51 +0800
From:   Wei Yang <richardw.yang@linux.intel.com>
To:     Baoquan He <bhe@redhat.com>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        akpm@linux-foundation.org, richardw.yang@linux.intel.com,
        david@redhat.com, osalvador@suse.de, dan.j.williams@intel.com,
        mhocko@suse.com, rppt@linux.ibm.com, robin.murphy@arm.com
Subject: Re: [PATCH v2 1/7] mm/hotplug: fix hot remove failure in
 SPARSEMEM|!VMEMMAP case
Message-ID: <20200220061151.GA32521@richard>
Reply-To: Wei Yang <richardw.yang@linux.intel.com>
References: <20200220043316.19668-1-bhe@redhat.com>
 <20200220043316.19668-2-bhe@redhat.com>
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On Thu, Feb 20, 2020 at 12:33:10PM +0800, 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.
>
>Signed-off-by: Baoquan He <bhe@redhat.com>

Reviewed-by: Wei Yang <richardw.yang@linux.intel.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,
>-- 
>2.17.2

-- 
Wei Yang
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