[PATCH 1/1] mm: vmalloc: dump page owner info if page is already mapped

[Hariom Panthi]

In vmap_pte_range, BUG_ON is called when page is already mapped,
It doesn't give enough information to debug further.
Dumping page owner information alongwith BUG_ON will be more useful
in case of multiple page mapping.

Example:
[   18.258806] page_owner tracks the page as allocated
[   18.258970] page last allocated via order 0, migratetype Unmovable, gfp_mask 0xcc0(GFP_KERNEL), pid 81, tgid 81 (insmod), ts 18257811008, free_ts 0
[   18.259327]  prep_new_page+0xa8/0x10c
[   18.259455]  get_page_from_freelist+0x7f8/0x1248
[   18.259591]  __alloc_pages+0x164/0x2b4
[   18.259703]  alloc_pages_mpol+0x88/0x230
[   18.259821]  alloc_pages+0x4c/0x7c
[   18.259923]  load_module+0x74/0x1af4
[   18.260031]  __do_sys_init_module+0x190/0x1fc
[   18.260154]  __arm64_sys_init_module+0x1c/0x28
[   18.260280]  invoke_syscall+0x44/0x108
[   18.260394]  el0_svc_common.constprop.0+0x40/0xe0
[   18.260530]  do_el0_svc_compat+0x1c/0x34
[   18.260647]  el0_svc_compat+0x2c/0x80
[   18.260761]  el0t_32_sync_handler+0x90/0x140
[   18.260887]  el0t_32_sync+0x194/0x198
[   18.260996] page_owner free stack trace missing
[   18.261143] ------------[ cut here ]------------
[   18.261272] kernel BUG at mm/vmalloc.c:113!

Signed-off-by: Hariom Panthi <hariom1.p@xxxxxxxxxxx>
---
 mm/vmalloc.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 68fa001648cc..9c91091887de 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -42,6 +42,7 @@
 #include <linux/sched/mm.h>
 #include <asm/tlbflush.h>
 #include <asm/shmparam.h>
+#include <linux/page_owner.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/vmalloc.h>
@@ -96,6 +97,7 @@ static int vmap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 {
 	pte_t *pte;
 	u64 pfn;
+	struct page *page;
 	unsigned long size = PAGE_SIZE;
 
 	pfn = phys_addr >> PAGE_SHIFT;
@@ -103,7 +105,13 @@ static int vmap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 	if (!pte)
 		return -ENOMEM;
 	do {
-		BUG_ON(!pte_none(ptep_get(pte)));
+		if (!pte_none(ptep_get(pte))) {
+			if (pfn_valid(pfn)) {
+				page = pfn_to_page(pfn);
+				dump_page_owner(page);
+			}
+			BUG();
+		}
 
 #ifdef CONFIG_HUGETLB_PAGE
 		size = arch_vmap_pte_range_map_size(addr, end, pfn, max_page_shift);
-- 
2.25.1