The patch titled Subject: mm/memory_hotplug: add missing mem_hotplug_lock has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-memory_hotplug-add-missing-mem_hotplug_lock.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Sumanth Korikkar sumanthk@linux.ibm.com Subject: mm/memory_hotplug: add missing mem_hotplug_lock Date: Mon, 20 Nov 2023 15:53:52 +0100

From Documentation/core-api/memory-hotplug.rst: When adding/removing/onlining/offlining memory or adding/removing heterogeneous/device memory, we should always hold the mem_hotplug_lock in write mode to serialise memory hotplug (e.g. access to global/zone variables).

mhp_(de)init_memmap_on_memory() functions can change zone stats and struct page content, but they are currently called w/o the mem_hotplug_lock.

When memory block is being offlined and when kmemleak goes through each populated zone, the following theoretical race conditions could occur: CPU 0: | CPU 1: memory_offline() | -> offline_pages() | -> mem_hotplug_begin() | ... | -> mem_hotplug_done() | | kmemleak_scan() | -> get_online_mems() | ... -> mhp_deinit_memmap_on_memory() | [not protected by mem_hotplug_begin/done()]| Marks memory section as offline, | Retrieves zone_start_pfn poisons vmemmap struct pages and updates | and struct page members. the zone related data | | ... | -> put_online_mems()

Fix this by ensuring mem_hotplug_lock is taken before performing mhp_init_memmap_on_memory(). Also ensure that mhp_deinit_memmap_on_memory() holds the lock.

online/offline_pages() are currently only called from memory_block_online/offline(), so it is safe to move the locking there.

Link: https://lkml.kernel.org/r/20231120145354.308999-2-sumanthk@linux.ibm.com Fixes: a08a2ae34613 ("mm,memory_hotplug: allocate memmap from the added memory range") Signed-off-by: Sumanth Korikkar sumanthk@linux.ibm.com Reviewed-by: Gerald Schaefer gerald.schaefer@linux.ibm.com Acked-by: David Hildenbrand david@redhat.com Cc: Alexander Gordeev agordeev@linux.ibm.com Cc: Aneesh Kumar K.V aneesh.kumar@linux.ibm.com Cc: Anshuman Khandual anshuman.khandual@arm.com Cc: Heiko Carstens hca@linux.ibm.com Cc: Michal Hocko mhocko@suse.com Cc: Oscar Salvador osalvador@suse.de Cc: Vasily Gorbik gor@linux.ibm.com Cc: kernel test robot lkp@intel.com Cc: stable@vger.kernel.org [5.15+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

drivers/base/memory.c | 18 +++++++++++++++--- mm/memory_hotplug.c | 13 ++++++------- 2 files changed, 21 insertions(+), 10 deletions(-)

--- a/drivers/base/memory.c~mm-memory_hotplug-add-missing-mem_hotplug_lock +++ a/drivers/base/memory.c @@ -180,6 +180,9 @@ static inline unsigned long memblk_nr_po } #endif

+/* + * Must acquire mem_hotplug_lock in write mode. + */ static int memory_block_online(struct memory_block *mem) { unsigned long start_pfn = section_nr_to_pfn(mem->start_section_nr); @@ -204,10 +207,11 @@ static int memory_block_online(struct me if (mem->altmap) nr_vmemmap_pages = mem->altmap->free;

+ mem_hotplug_begin(); if (nr_vmemmap_pages) { ret = mhp_init_memmap_on_memory(start_pfn, nr_vmemmap_pages, zone); if (ret) - return ret; + goto out; }

ret = online_pages(start_pfn + nr_vmemmap_pages, @@ -215,7 +219,7 @@ static int memory_block_online(struct me if (ret) { if (nr_vmemmap_pages) mhp_deinit_memmap_on_memory(start_pfn, nr_vmemmap_pages); - return ret; + goto out; }

/* @@ -227,9 +231,14 @@ static int memory_block_online(struct me nr_vmemmap_pages);

mem->zone = zone; +out: + mem_hotplug_done(); return ret; }

+/* + * Must acquire mem_hotplug_lock in write mode. + */ static int memory_block_offline(struct memory_block *mem) { unsigned long start_pfn = section_nr_to_pfn(mem->start_section_nr); @@ -247,6 +256,7 @@ static int memory_block_offline(struct m if (mem->altmap) nr_vmemmap_pages = mem->altmap->free;

+ mem_hotplug_begin(); if (nr_vmemmap_pages) adjust_present_page_count(pfn_to_page(start_pfn), mem->group, -nr_vmemmap_pages); @@ -258,13 +268,15 @@ static int memory_block_offline(struct m if (nr_vmemmap_pages) adjust_present_page_count(pfn_to_page(start_pfn), mem->group, nr_vmemmap_pages); - return ret; + goto out; }

if (nr_vmemmap_pages) mhp_deinit_memmap_on_memory(start_pfn, nr_vmemmap_pages);

mem->zone = NULL; +out: + mem_hotplug_done(); return ret; }

--- a/mm/memory_hotplug.c~mm-memory_hotplug-add-missing-mem_hotplug_lock +++ a/mm/memory_hotplug.c @@ -1129,6 +1129,9 @@ void mhp_deinit_memmap_on_memory(unsigne kasan_remove_zero_shadow(__va(PFN_PHYS(pfn)), PFN_PHYS(nr_pages)); }

+/* + * Must be called with mem_hotplug_lock in write mode. + */ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, struct zone *zone, struct memory_group *group) { @@ -1149,7 +1152,6 @@ int __ref online_pages(unsigned long pfn !IS_ALIGNED(pfn + nr_pages, PAGES_PER_SECTION))) return -EINVAL;

- mem_hotplug_begin();

/* associate pfn range with the zone */ move_pfn_range_to_zone(zone, pfn, nr_pages, NULL, MIGRATE_ISOLATE); @@ -1208,7 +1210,6 @@ int __ref online_pages(unsigned long pfn writeback_set_ratelimit();

memory_notify(MEM_ONLINE, &arg); - mem_hotplug_done(); return 0;

failed_addition: @@ -1217,7 +1218,6 @@ failed_addition: (((unsigned long long) pfn + nr_pages) << PAGE_SHIFT) - 1); memory_notify(MEM_CANCEL_ONLINE, &arg); remove_pfn_range_from_zone(zone, pfn, nr_pages); - mem_hotplug_done(); return ret; }

@@ -1863,6 +1863,9 @@ static int count_system_ram_pages_cb(uns return 0; }

+/* + * Must be called with mem_hotplug_lock in write mode. + */ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages, struct zone *zone, struct memory_group *group) { @@ -1885,8 +1888,6 @@ int __ref offline_pages(unsigned long st !IS_ALIGNED(start_pfn + nr_pages, PAGES_PER_SECTION))) return -EINVAL;

- mem_hotplug_begin(); - /* * Don't allow to offline memory blocks that contain holes. * Consequently, memory blocks with holes can never get onlined @@ -2031,7 +2032,6 @@ int __ref offline_pages(unsigned long st

memory_notify(MEM_OFFLINE, &arg); remove_pfn_range_from_zone(zone, start_pfn, nr_pages); - mem_hotplug_done(); return 0;

failed_removal_isolated: @@ -2046,7 +2046,6 @@ failed_removal: (unsigned long long) start_pfn << PAGE_SHIFT, ((unsigned long long) end_pfn << PAGE_SHIFT) - 1, reason); - mem_hotplug_done(); return ret; }

_

Patches currently in -mm which might be from sumanthk@linux.ibm.com are

mm-memory_hotplug-add-missing-mem_hotplug_lock.patch mm-memory_hotplug-fix-error-handling-in-add_memory_resource.patch mm-use-vmem_altmap-code-without-config_zone_device.patch