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Subject[PATCH v3 1/7] mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case
Date
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@redhat.com>
Cc: stable@vger.kernel.org
---
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
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