The patch titled
Subject: mm/memory_hotplug.c: refactor unregister_mem_sect_under_nodes
has been added to the -mm tree. Its filename is
mm-memory_hotplug-refactor-unregister_mem_sect_under_nodes.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-memory_hotplug-refactor-unregister_mem_sect_under_nodes.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-memory_hotplug-refactor-unregister_mem_sect_under_nodes.patch
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------------------------------------------------------
From: Oscar Salvador <osalvador@xxxxxxx>
Subject: mm/memory_hotplug.c: refactor unregister_mem_sect_under_nodes
unregister_mem_sect_under_nodes() tries to allocate a nodemask_t in order
to check within the loop which nodes have already been unlinked, so we do
not repeat the operation on them.
NODEMASK_ALLOC calls kmalloc() if NODES_SHIFT > 8, otherwise it just
declares a nodemask_t variable whithin the stack.
Since kmalloc() can fail, we actually check whether NODEMASK_ALLOC failed
or not, and we return -ENOMEM accordingly. remove_memory_section() does
not check for the return value though.
The problem with this is that if we return -ENOMEM, it means that
unregister_mem_sect_under_nodes will not be able to remove the symlinks,
but since we do not check the return value, we go ahead and we call
unregister_memory(), which will remove all the mem_blks directories.
This will leave us with dangled symlinks.
The easiest way to overcome this is to fallback by calling
sysfs_remove_link() unconditionally in case NODEMASK_ALLOC failed. This
means that we will call sysfs_remove_link on nodes that have been already
unlinked, but nothing wrong happens as sysfs_remove_link() backs off
somewhere down the chain in case the link has already been removed.
I think that this is better than
a) dangled symlinks
b) having to recovery from such error in remove_memory_section
Since from now on we will not need to care about return values, we can make
the function void.
As we have a safe fallback, one thing that could also be done is to add
__GFP_NORETRY in the flags when calling NODEMASK_ALLOC, so we do not retry.
Link: http://lkml.kernel.org/r/20180815144219.6014-4-osalvador@xxxxxxxxxxxxxxxxxx
Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Jonathan Cameron <jonathan.cameron@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: <yasu.isimatu@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/base/node.c | 23 +++++++++++++++--------
include/linux/node.h | 5 ++---
2 files changed, 17 insertions(+), 11 deletions(-)
--- a/drivers/base/node.c~mm-memory_hotplug-refactor-unregister_mem_sect_under_nodes
+++ a/drivers/base/node.c
@@ -449,35 +449,42 @@ int register_mem_sect_under_node(struct
}
/* unregister memory section under all nodes that it spans */
-int unregister_mem_sect_under_nodes(struct memory_block *mem_blk,
+void unregister_mem_sect_under_nodes(struct memory_block *mem_blk,
unsigned long phys_index)
{
NODEMASK_ALLOC(nodemask_t, unlinked_nodes, GFP_KERNEL);
unsigned long pfn, sect_start_pfn, sect_end_pfn;
- if (!unlinked_nodes)
- return -ENOMEM;
- nodes_clear(*unlinked_nodes);
+ if (unlinked_nodes)
+ nodes_clear(*unlinked_nodes);
sect_start_pfn = section_nr_to_pfn(phys_index);
sect_end_pfn = sect_start_pfn + PAGES_PER_SECTION - 1;
for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) {
- int nid;
+ int nid = get_nid_for_pfn(pfn);
- nid = get_nid_for_pfn(pfn);
if (nid < 0)
continue;
if (!node_online(nid))
continue;
- if (node_test_and_set(nid, *unlinked_nodes))
+ /*
+ * It is possible that NODEMASK_ALLOC fails due to memory
+ * pressure.
+ * If that happens, we fallback to call sysfs_remove_link
+ * unconditionally.
+ * Nothing wrong will happen as sysfs_remove_link will back off
+ * somewhere down the chain in case the link has already been
+ * removed.
+ */
+ if (unlinked_nodes && node_test_and_set(nid, *unlinked_nodes))
continue;
+
sysfs_remove_link(&node_devices[nid]->dev.kobj,
kobject_name(&mem_blk->dev.kobj));
sysfs_remove_link(&mem_blk->dev.kobj,
kobject_name(&node_devices[nid]->dev.kobj));
}
NODEMASK_FREE(unlinked_nodes);
- return 0;
}
int link_mem_sections(int nid, unsigned long start_pfn, unsigned long end_pfn)
--- a/include/linux/node.h~mm-memory_hotplug-refactor-unregister_mem_sect_under_nodes
+++ a/include/linux/node.h
@@ -72,7 +72,7 @@ extern int register_cpu_under_node(unsig
extern int unregister_cpu_under_node(unsigned int cpu, unsigned int nid);
extern int register_mem_sect_under_node(struct memory_block *mem_blk,
void *arg);
-extern int unregister_mem_sect_under_nodes(struct memory_block *mem_blk,
+extern void unregister_mem_sect_under_nodes(struct memory_block *mem_blk,
unsigned long phys_index);
#ifdef CONFIG_HUGETLBFS
@@ -105,10 +105,9 @@ static inline int register_mem_sect_unde
{
return 0;
}
-static inline int unregister_mem_sect_under_nodes(struct memory_block *mem_blk,
+static inline void unregister_mem_sect_under_nodes(struct memory_block *mem_blk,
unsigned long phys_index)
{
- return 0;
}
static inline void register_hugetlbfs_with_node(node_registration_func_t reg,
_
Patches currently in -mm which might be from osalvador@xxxxxxx are
mm-memory_hotplug-make-add_memory_resource-use-__try_online_node.patch
mm-memory_hotplug-call-register_mem_sect_under_node.patch
mm-memory_hotplug-make-register_mem_sect_under_node-a-cb-of-walk_memory_range.patch
mm-memory_hotplug-drop-unnecessary-checks-from-register_mem_sect_under_node.patch
mm-sparse-make-sparse_init_one_section-void-and-remove-check.patch
mm-remove-zone_id-and-make-use-of-zone_idx-in-is_dev_zone.patch
mm-page_alloc-move-ifdefery-out-of-free_area_init_core.patch
mm-page_alloc-inline-function-to-handle-config_deferred_struct_page_init.patch
mm-page_alloc-introduce-free_area_init_core_hotplug.patch
mm-page_alloc-introduce-free_area_init_core_hotplug-v6.patch
mm-memory_hotplug-drop-unused-args-from-remove_memory_section.patch
mm-memory_hotplug-drop-unneeded-check-from-unregister_mem_sect_under_nodes.patch
mm-memory_hotplug-refactor-unregister_mem_sect_under_nodes.patch
mm-memory_hotplug-drop-node_online-check-in-unregister_mem_sect_under_nodes.patch
