From 0706d8840c9f6705dbbc680b29276d2bfcaff681 Mon Sep 17 00:00:00 2001 From: Wei Yang Date: Tue, 22 Sep 2020 10:17:35 +0800 Subject: [PATCH] mm, sparse: drop pgdat_resize_lock in sparse_add/remove_one_section() stable inclusion from linux-4.19.100 commit b1dbaa19162857eeb8cd751e58394d1c8c34b12e -------------------------------- commit 83af658898cb292a32d8b6cd9b51266d7cfc4b6a upstream. pgdat_resize_lock is used to protect pgdat's memory region information like: node_start_pfn, node_present_pages, etc. While in function sparse_add/remove_one_section(), pgdat_resize_lock is used to protect initialization/release of one mem_section. This looks not proper. These code paths are currently protected by mem_hotplug_lock currently but should there ever be any reason for locking at the sparse layer a dedicated lock should be introduced. Following is the current call trace of sparse_add/remove_one_section() mem_hotplug_begin() arch_add_memory() add_pages() __add_pages() __add_section() sparse_add_one_section() mem_hotplug_done() mem_hotplug_begin() arch_remove_memory() __remove_pages() __remove_section() sparse_remove_one_section() mem_hotplug_done() The comment above the pgdat_resize_lock also mentions "Holding this will also guarantee that any pfn_valid() stays that way.", which is true with the current implementation and false after this patch. But current implementation doesn't meet this comment. There isn't any pfn walkers to take the lock so this looks like a relict from the past. This patch also removes this comment. [richard.weiyang@gmail.com: v4] Link: http://lkml.kernel.org/r/20181204085657.20472-1-richard.weiyang@gmail.com [mhocko@suse.com: changelog suggestion] Link: http://lkml.kernel.org/r/20181128091243.19249-1-richard.weiyang@gmail.com Signed-off-by: Wei Yang Reviewed-by: David Hildenbrand Acked-by: Michal Hocko Cc: Dave Hansen Cc: Oscar Salvador Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: David Hildenbrand Signed-off-by: Greg Kroah-Hartman Signed-off-by: Yang Yingliang --- include/linux/mmzone.h | 3 +-- mm/sparse.c | 9 +-------- 2 files changed, 2 insertions(+), 10 deletions(-) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 390dece16b60..9c6181b78bfd 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -641,8 +641,7 @@ typedef struct pglist_data { #if defined(CONFIG_MEMORY_HOTPLUG) || defined(CONFIG_DEFERRED_STRUCT_PAGE_INIT) /* * Must be held any time you expect node_start_pfn, node_present_pages - * or node_spanned_pages stay constant. Holding this will also - * guarantee that any pfn_valid() stays that way. + * or node_spanned_pages stay constant. * * pgdat_resize_lock() and pgdat_resize_unlock() are provided to * manipulate node_size_lock without checking for CONFIG_MEMORY_HOTPLUG diff --git a/mm/sparse.c b/mm/sparse.c index 504c3ea11561..0599e7f8be83 100644 --- a/mm/sparse.c +++ b/mm/sparse.c @@ -678,7 +678,6 @@ int __meminit sparse_add_one_section(struct pglist_data *pgdat, struct mem_section *ms; struct page *memmap; unsigned long *usemap; - unsigned long flags; int ret; /* @@ -698,8 +697,6 @@ int __meminit sparse_add_one_section(struct pglist_data *pgdat, return -ENOMEM; } - pgdat_resize_lock(pgdat, &flags); - ms = __pfn_to_section(start_pfn); if (ms->section_mem_map & SECTION_MARKED_PRESENT) { ret = -EEXIST; @@ -718,7 +715,6 @@ int __meminit sparse_add_one_section(struct pglist_data *pgdat, sparse_init_one_section(ms, section_nr, memmap, usemap); out: - pgdat_resize_unlock(pgdat, &flags); if (ret < 0) { kfree(usemap); __kfree_section_memmap(memmap, altmap); @@ -780,10 +776,8 @@ void sparse_remove_one_section(struct zone *zone, struct mem_section *ms, unsigned long map_offset, struct vmem_altmap *altmap) { struct page *memmap = NULL; - unsigned long *usemap = NULL, flags; - struct pglist_data *pgdat = zone->zone_pgdat; + unsigned long *usemap = NULL; - pgdat_resize_lock(pgdat, &flags); if (ms->section_mem_map) { usemap = ms->pageblock_flags; memmap = sparse_decode_mem_map(ms->section_mem_map, @@ -791,7 +785,6 @@ void sparse_remove_one_section(struct zone *zone, struct mem_section *ms, ms->section_mem_map = 0; ms->pageblock_flags = NULL; } - pgdat_resize_unlock(pgdat, &flags); clear_hwpoisoned_pages(memmap + map_offset, PAGES_PER_SECTION - map_offset); -- GitLab