From: David Hildenbrand <david@xxxxxxxxxx>
Subject: mm/memory_hotplug: fix try_offline_node()
try_offline_node() is pretty much broken right now:
- The node span is updated when onlining memory, not when adding it. We
ignore memory that was mever onlined. Bad.
- We touch possible garbage memmaps. The pfn_to_nid(pfn) can easily
trigger a kernel panic. Bad for memory that is offline but also bad for
subsection hotadd with ZONE_DEVICE, whereby the memmap of the first PFN
of a section might contain garbage.
- Sections belonging to mixed nodes are not properly considered.
As memory blocks might belong to multiple nodes, we would have to walk all
pageblocks (or at least subsections) within present sections. However, we
don't have a way to identify whether a memmap that is not online was
initialized (relevant for ZONE_DEVICE). This makes things more
complicated.
Luckily, we can piggy pack on the node span and the nid stored in memory
blocks. Currently, the node span is grown when calling
move_pfn_range_to_zone() - e.g., when onlining memory, and shrunk when
removing memory, before calling try_offline_node(). Sysfs links are
created via link_mem_sections(), e.g., during boot or when adding memory.
If the node still spans memory or if any memory block belongs to the nid,
we don't set the node offline. As memory blocks that span multiple nodes
cannot get offlined, the nid stored in memory blocks is reliable enough
(for such online memory blocks, the node still spans the memory).
Introduce for_each_memory_block() to efficiently walk all memory blocks.
Note: We will soon stop shrinking the ZONE_DEVICE zone and the node span
when removing ZONE_DEVICE memory to fix similar issues (access of garbage
memmaps) - until we have a reliable way to identify whether these memmaps
were properly initialized. This implies later, that once a node had
ZONE_DEVICE memory, we won't be able to set a node offline - which should
be acceptable.
Since commit f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded
memory to zones until online") memory that is added is not assoziated with
a zone/node (memmap not initialized). The introducing commit 60a5a19e7419
("memory-hotplug: remove sysfs file of node") already missed that we could
have multiple nodes for a section and that the zone/node span is updated
when onlining pages, not when adding them.
I tested this by hotplugging two DIMMs to a memory-less and cpu-less NUMA
node. The node is properly onlined when adding the DIMMs. When removing
the DIMMs, the node is properly offlined.
Masayoshi Mizuma reported:
: Without this patch, memory hotplug fails as panic:
:
: BUG: kernel NULL pointer dereference, address: 0000000000000000
: ...
: Call Trace:
: remove_memory_block_devices+0x81/0xc0
: try_remove_memory+0xb4/0x130
: ? walk_memory_blocks+0x75/0xa0
: __remove_memory+0xa/0x20
: acpi_memory_device_remove+0x84/0x100
: acpi_bus_trim+0x57/0x90
: acpi_bus_trim+0x2e/0x90
: acpi_device_hotplug+0x2b2/0x4d0
: acpi_hotplug_work_fn+0x1a/0x30
: process_one_work+0x171/0x380
: worker_thread+0x49/0x3f0
: kthread+0xf8/0x130
: ? max_active_store+0x80/0x80
: ? kthread_bind+0x10/0x10
: ret_from_fork+0x35/0x40
[david@xxxxxxxxxx: v3]
Link: http://lkml.kernel.org/r/20191102120221.7553-1-david@xxxxxxxxxx
Link: http://lkml.kernel.org/r/20191028105458.28320-1-david@xxxxxxxxxx
Fixes: 60a5a19e7419 ("memory-hotplug: remove sysfs file of node")
Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to zones until online") # visiable after d0dc12e86b319
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Tested-by: Masayoshi Mizuma <m.mizuma@xxxxxxxxxxxxxx>
Cc: Tang Chen <tangchen@xxxxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
Cc: Keith Busch <keith.busch@xxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: "Peter Zijlstra (Intel)" <peterz@xxxxxxxxxxxxx>
Cc: Jani Nikula <jani.nikula@xxxxxxxxx>
Cc: Nayna Jain <nayna@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/base/memory.c | 36 +++++++++++++++++++++++++++++
include/linux/memory.h | 1
mm/memory_hotplug.c | 47 ++++++++++++++++++++++++---------------
3 files changed, 66 insertions(+), 18 deletions(-)
--- a/drivers/base/memory.c~mm-memory_hotplug-fix-try_offline_node
+++ a/drivers/base/memory.c
@@ -872,3 +872,39 @@ int walk_memory_blocks(unsigned long sta
}
return ret;
}
+
+struct for_each_memory_block_cb_data {
+ walk_memory_blocks_func_t func;
+ void *arg;
+};
+
+static int for_each_memory_block_cb(struct device *dev, void *data)
+{
+ struct memory_block *mem = to_memory_block(dev);
+ struct for_each_memory_block_cb_data *cb_data = data;
+
+ return cb_data->func(mem, cb_data->arg);
+}
+
+/**
+ * for_each_memory_block - walk through all present memory blocks
+ *
+ * @arg: argument passed to func
+ * @func: callback for each memory block walked
+ *
+ * This function walks through all present memory blocks, calling func on
+ * each memory block.
+ *
+ * In case func() returns an error, walking is aborted and the error is
+ * returned.
+ */
+int for_each_memory_block(void *arg, walk_memory_blocks_func_t func)
+{
+ struct for_each_memory_block_cb_data cb_data = {
+ .func = func,
+ .arg = arg,
+ };
+
+ return bus_for_each_dev(&memory_subsys, NULL, &cb_data,
+ for_each_memory_block_cb);
+}
--- a/include/linux/memory.h~mm-memory_hotplug-fix-try_offline_node
+++ a/include/linux/memory.h
@@ -119,6 +119,7 @@ extern struct memory_block *find_memory_
typedef int (*walk_memory_blocks_func_t)(struct memory_block *, void *);
extern int walk_memory_blocks(unsigned long start, unsigned long size,
void *arg, walk_memory_blocks_func_t func);
+extern int for_each_memory_block(void *arg, walk_memory_blocks_func_t func);
#define CONFIG_MEM_BLOCK_SIZE (PAGES_PER_SECTION<<PAGE_SHIFT)
#endif /* CONFIG_MEMORY_HOTPLUG_SPARSE */
--- a/mm/memory_hotplug.c~mm-memory_hotplug-fix-try_offline_node
+++ a/mm/memory_hotplug.c
@@ -1646,6 +1646,18 @@ static int check_cpu_on_node(pg_data_t *
return 0;
}
+static int check_no_memblock_for_node_cb(struct memory_block *mem, void *arg)
+{
+ int nid = *(int *)arg;
+
+ /*
+ * If a memory block belongs to multiple nodes, the stored nid is not
+ * reliable. However, such blocks are always online (e.g., cannot get
+ * offlined) and, therefore, are still spanned by the node.
+ */
+ return mem->nid == nid ? -EEXIST : 0;
+}
+
/**
* try_offline_node
* @nid: the node ID
@@ -1658,25 +1670,24 @@ static int check_cpu_on_node(pg_data_t *
void try_offline_node(int nid)
{
pg_data_t *pgdat = NODE_DATA(nid);
- unsigned long start_pfn = pgdat->node_start_pfn;
- unsigned long end_pfn = start_pfn + pgdat->node_spanned_pages;
- unsigned long pfn;
-
- for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
- unsigned long section_nr = pfn_to_section_nr(pfn);
-
- if (!present_section_nr(section_nr))
- continue;
-
- if (pfn_to_nid(pfn) != nid)
- continue;
-
- /*
- * some memory sections of this node are not removed, and we
- * can't offline node now.
- */
+ int rc;
+
+ /*
+ * If the node still spans pages (especially ZONE_DEVICE), don't
+ * offline it. A node spans memory after move_pfn_range_to_zone(),
+ * e.g., after the memory block was onlined.
+ */
+ if (pgdat->node_spanned_pages)
+ return;
+
+ /*
+ * Especially offline memory blocks might not be spanned by the
+ * node. They will get spanned by the node once they get onlined.
+ * However, they link to the node in sysfs and can get onlined later.
+ */
+ rc = for_each_memory_block(&nid, check_no_memblock_for_node_cb);
+ if (rc)
return;
- }
if (check_cpu_on_node(pgdat))
return;
_
