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

[Andrew Morton]

On Fri, 19 Apr 2024 10:09:10 +0530 Hariom Panthi <hariom1.p@xxxxxxxxxxx> wrote:

> 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!
> 
> ...
>
> @@ -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();
> +		}

Diving straight into dump_page_owner() seems inappropriate.  The
higher-level dump_page() interface is more typically used.

Or, even more common, VM_BUG_ON_PAGE(), but that doesn't look to be a
good fit here.