Re: Report a huge page issue in kernel version v5.19.xx

[Muchun Song <muchun.song@linux.dev>]

> On Jul 3, 2023, at 11:07, Fumin Gao <Fumin.Gao@viavisolutions.com> wrote:
> 
> Hi,  What’s the issue?
> Recently in our product, I found a issue in kernel version v5.19.xx, this issue was fixed in kernel version v6.xx.
> The issue is I can’t get which node the huge page is on by system call move_pages.
>  How to reproduce this issue? 
> I attached my test programme file in email.
> virtaddr = mmap(NULL, ONE_GIG, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB , -1, 0);
> *(char *)virtaddr = 0;
> if (syscall(SYS_move_pages, 0, 1, &virtaddr, NULL, &NumaNode, 0) != 0)
> {
>    printf("Get virtual address 0x%p on NumaNode failed \n", virtaddr);
> }
> printf("create shared memory with mmap, virtaddr 0x%lx on Node %d, errno %d \n", virtaddr,NumaNode, errno);
>  When tested with kernel v5.19.xx , the value of  NumaNode is -2 (-ENOENT).
>  My analysis of this issue.
> Based on the following trace and kernel source code, I can see the function calling process.
> kernel_move_pages – do_pages_stat –  do_pages_stat_array — follow_page — follow_page_mask
> — follow_p4d_mask — follow_pud_mask — follow_huge_pud
>  [001] ..... 510329749178328: sys_move_pages(pid: 0, nr_pages: 1, pages: 7fffa23a2c90, nodes: 0, status: 7fffa23a2c9c, flags: 0)
> [001] ..... 510329749179360: sys_enter: NR 279 (0, 1, 7fffa23a2c90, 0, 7fffa23a2c9c, 0)
> [001] ...1. 510329749185448: mmap_lock_start_locking: mm=00000000e0f35bcd memcg_path=/user.slice/user-1000.slice/session-1.scope write=false
> [001] ...1. 510329749187872: mmap_lock_acquire_returned: mm=00000000e0f35bcd memcg_path=/user.slice/user-1000.slice/session-1.scope write=false success=true
> [001] ..... 510329749196628: p_follow_page_0: (follow_page+0x0/0xe0)
> [001] ..... 510329749199690: p_vma_is_secretmem_0: (vma_is_secretmem+0x0/0x20)
> [001] ..... 510329749202194: p_follow_page_mask_0: (follow_page_mask+0x0/0x160)
> [001] ..... 510329749206928: p_follow_huge_addr_0: (follow_huge_addr+0x0/0x20)
> [001] ..... 510329749210628: myretprobe: (follow_page_mask+0x38/0x160 <- follow_huge_addr) ret=0xffffffffffffffea
> [001] ..... 510329749216464: p_follow_pud_mask_isra_0_0: (follow_pud_mask.isra.0+0x0/0x1e0)
> [001] ..... 510329749221108: p_follow_huge_pud_0: (follow_huge_pud+0x0/0x80)
> [001] ..... 510329749221902: myretprobe: (follow_pud_mask.isra.0+0x1c8/0x1e0 <- follow_huge_pud) ret=0x0
> [001] ..... 510329749223462: myretprobe: (follow_page_mask+0x147/0x160 <- follow_pud_mask.isra.0) ret=0x0
> [001] ..... 510329749224838: myretprobe: (do_pages_stat+0x18b/0x330 <- follow_page) ret=0x0
> [001] ...1. 510329749226096: mmap_lock_released: mm=00000000e0f35bcd memcg_path=/user.slice/user-1000.slice/session-1.scope write=false
> [001] ..... 510329749228348: sys_move_pages -> 0x0
> [001] ..... 510329749229224: sys_exit: NR 279 = 0
>  In the kernel version v5.19.xx, it add a flag FOLL_GET  in do_pages_stat_array compared with v5.18.xx.
>         page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP);
>  But in the function follow_huge_pud, if the flags has FOLL_GET, it will return NULL. This causes we get the status is -ENOENT (-2) 
> in move_pages.
>   Is my analysis correct ?

Correct! If you want v5.19 works properly, you could apply

  commit 831568214883 ("mm: migration: fix the FOLL_GET failure on following huge page")

to fix the issue.

Thanks.