[PATCH v2 01/69] mm/hugetlb: Fix boot panic with CONFIG_DEBUG_VM and HVO bootmem pages

[Muchun Song <songmuchun@bytedance.com>]

Commit 622026e87c40 ("mm/hugetlb: remove fake head pages") switched
HVO to reuse per-zone shared tail pages from zone->vmemmap_tails[].

Those shared tail pages were initialized in hugetlb_vmemmap_init(), but
bootmem HugeTLB folios are prepared earlier from gather_bootmem_prealloc().
With hugetlb_free_vmemmap=on, prep_and_add_bootmem_folios() can access
pageblock flags on bootmem HugeTLB pages whose mirrored tail struct pages
already point to the shared tail page. On CONFIG_DEBUG_VM kernels,
get_pfnblock_bitmap_bitidx() then dereferences the still-uninitialized
shared tail page and can panic during boot.

Initialize zone->vmemmap_tails[] from gather_bootmem_prealloc(), before
bootmem HugeTLB folios are processed, and drop the later initialization
from hugetlb_vmemmap_init().

This bug only affects CONFIG_DEBUG_VM kernels, where the relevant
assertion is evaluated.

Fixes: 622026e87c40 ("mm/hugetlb: remove fake head pages")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 mm/hugetlb.c         | 19 +++++++++++++++++++
 mm/hugetlb_vmemmap.c | 17 -----------------
 2 files changed, 19 insertions(+), 17 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 31b34ca0f402..d22683ab30a1 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3382,6 +3382,25 @@ static void __init gather_bootmem_prealloc(void)
 		.max_threads	= num_node_state(N_MEMORY),
 		.numa_aware	= true,
 	};
+#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
+	struct zone *zone;
+
+	for_each_zone(zone) {
+		for (int i = 0; i < NR_VMEMMAP_TAILS; i++) {
+			struct page *tail, *p;
+			unsigned int order;
+
+			tail = zone->vmemmap_tails[i];
+			if (!tail)
+				continue;
+
+			order = i + VMEMMAP_TAIL_MIN_ORDER;
+			p = page_to_virt(tail);
+			for (int j = 0; j < PAGE_SIZE / sizeof(struct page); j++)
+				init_compound_tail(p + j, NULL, order, zone);
+		}
+	}
+#endif
 
 	padata_do_multithreaded(&job);
 }
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 4a077d231d3a..62e61af18c9a 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -870,27 +870,10 @@ static const struct ctl_table hugetlb_vmemmap_sysctls[] = {
 static int __init hugetlb_vmemmap_init(void)
 {
 	const struct hstate *h;
-	struct zone *zone;
 
 	/* HUGETLB_VMEMMAP_RESERVE_SIZE should cover all used struct pages */
 	BUILD_BUG_ON(__NR_USED_SUBPAGE > HUGETLB_VMEMMAP_RESERVE_PAGES);
 
-	for_each_zone(zone) {
-		for (int i = 0; i < NR_VMEMMAP_TAILS; i++) {
-			struct page *tail, *p;
-			unsigned int order;
-
-			tail = zone->vmemmap_tails[i];
-			if (!tail)
-				continue;
-
-			order = i + VMEMMAP_TAIL_MIN_ORDER;
-			p = page_to_virt(tail);
-			for (int j = 0; j < PAGE_SIZE / sizeof(struct page); j++)
-				init_compound_tail(p + j, NULL, order, zone);
-		}
-	}
-
 	for_each_hstate(h) {
 		if (hugetlb_vmemmap_optimizable(h)) {
 			register_sysctl_init("vm", hugetlb_vmemmap_sysctls);
-- 
2.54.0