path: root/mm/memory_hotplug.c
diff options
authorDavid Hildenbrand <david@redhat.com>2019-11-15 17:34:57 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2019-11-15 18:34:00 -0800
commit2c91f8fc6c999fe10185d8ad99fda1759f662f70 (patch)
tree1436506806abb23d045091ed5dea9d59ae6086d4 /mm/memory_hotplug.c
parentmm,thp: recheck each page before collapsing file THP (diff)
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 : __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 : ret_from_fork+0x35/0x40 [david@redhat.com: v3] Link: http://lkml.kernel.org/r/20191102120221.7553-1-david@redhat.com Link: http://lkml.kernel.org/r/20191028105458.28320-1-david@redhat.com 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@redhat.com> Tested-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com> Cc: Tang Chen <tangchen@cn.fujitsu.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: "Rafael J. Wysocki" <rafael@kernel.org> Cc: Keith Busch <keith.busch@intel.com> Cc: Jiri Olsa <jolsa@kernel.org> Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org> Cc: Jani Nikula <jani.nikula@intel.com> Cc: Nayna Jain <nayna@linux.ibm.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: Stephen Rothwell <sfr@canb.auug.org.au> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Pavel Tatashin <pasha.tatashin@soleen.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to '')
1 files changed, 27 insertions, 16 deletions
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 07e5c67f48a8..3b62a9ff8ea0 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1646,6 +1646,18 @@ static int check_cpu_on_node(pg_data_t *pgdat)
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 *pgdat)
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;
+ int rc;
- if (pfn_to_nid(pfn) != nid)
- continue;
+ /*
+ * 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;
- /*
- * some memory sections of this node are not removed, and we
- * can't offline node now.
- */
+ /*
+ * 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)
- }
if (check_cpu_on_node(pgdat))