Re: [RFC PATCH v1 4/7] mm/memory_failure: unmap raw HWPoison PTEs when possible

["HORIGUCHI NAOYA(堀口 直也)" <naoya.horiguchi@nec.com>]

On Fri, Apr 28, 2023 at 12:41:36AM +0000, Jiaqi Yan wrote:
> When a folio's VMA is HGM eligible, try_to_unmap_one now only unmaps
> the raw HWPOISON page (previously split and mapped at PTE size).
> If HGM failed to be enabled on eligible VMA or splitting failed,
> try_to_unmap_one fails.
> 
> For VMS that is not HGM eligible, try_to_unmap_one still unmaps
> the whole P*D.
> 
> When only the raw HWPOISON subpage is unmapped but others keep mapped,
> the old way in memory_failure to check if unmapping successful doesn't
> work. So introduce is_unmapping_successful() to cover both existing and
> new unmapping behavior.
> 
> For the new unmapping behavior, store how many times a raw HWPOISON page
> is expected to be unmapped, and how many times it is actually unmapped
> in try_to_unmap_one(). A HWPOISON raw page is expected to be unmapped
> from a VMA if splitting succeeded in try_to_split_huge_mapping(), so
> unmap_success = (nr_expected_unamps == nr_actual_unmaps).
> 
> Old folio_set_hugetlb_hwpoison returns -EHWPOISON if a folio has any
> raw HWPOISON subpage, and try_memory_failure_hugetlb won't attempt
> recovery actions again because recovery used to be done on the entire
> hugepage. With the new unmapping behavior, this doesn't hold. More
> subpages in the hugepage can become corrupted, and needs to be recovered
> (i.e. unmapped) individually. New folio_set_hugetlb_hwpoison returns
> 0 after adding a new raw subpage to raw_hwp_list.
> 
> Unmapping raw HWPOISON page requires allocating raw_hwp_page
> successfully in folio_set_hugetlb_hwpoison, so try_memory_failure_hugetlb
> now may fail due to OOM.
> 
> Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
> ---
...

> @@ -1827,6 +1879,31 @@ EXPORT_SYMBOL_GPL(mf_dax_kill_procs);
>  
>  #ifdef CONFIG_HUGETLB_PAGE
>  
> +/*
> + * Given a HWPOISON @subpage as raw page, find its location in @folio's
> + * _hugetlb_hwpoison. Return NULL if @subpage is not in the list.
> + */
> +struct raw_hwp_page *find_in_raw_hwp_list(struct folio *folio,
> +					  struct page *subpage)
> +{
> +	struct llist_node *t, *tnode;
> +	struct llist_head *raw_hwp_head = raw_hwp_list_head(folio);
> +	struct raw_hwp_page *hwp_page = NULL;
> +	struct raw_hwp_page *p;
> +
> +	VM_BUG_ON_PAGE(PageHWPoison(subpage), subpage);

I'm testing the series (on top of v6.2-rc4 + HGM v2 patchset) and found the
following error triggered by this VM_BUG_ON_PAGE().  The testcase is just to
inject hwpoison on an anonymous page (it's not hugetlb-related one).

  [  790.610985] ===> testcase 'mm/hwpoison/base/backend-anonymous_error-hard-offline_access-avoid.auto3' start
  [  793.304927] page:000000006743177b refcount:1 mapcount:0 mapping:0000000000000000 index:0x700000000 pfn:0x14d739
  [  793.309322] memcg:ffff8a30c50b6000
  [  793.310934] anon flags: 0x57ffffe08a001d(locked|uptodate|dirty|lru|mappedtodisk|swapbacked|hwpoison|node=1|zone=2|lastcpupid=0x1fffff)
  [  793.316665] raw: 0057ffffe08a001d ffffe93cc5353c88 ffffe93cc5685fc8 ffff8a30c91878f1
  [  793.320211] raw: 0000000700000000 0000000000000000 00000001ffffffff ffff8a30c50b6000
  [  793.323665] page dumped because: VM_BUG_ON_PAGE(PageHWPoison(subpage))
  [  793.326764] ------------[ cut here ]------------
  [  793.329080] kernel BUG at mm/memory-failure.c:1894!
  [  793.331895] invalid opcode: 0000 [#1] PREEMPT SMP PTI
  [  793.334854] CPU: 4 PID: 2644 Comm: mceinj.sh Tainted: G            E    N 6.2.0-rc4-v6.2-rc2-230529-1404+ #63
  [  793.340710] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.1-2.fc37 04/01/2014
  [  793.345875] RIP: 0010:hwpoison_user_mappings+0x654/0x780
  [  793.349066] Code: ef 89 de e8 6e bc f8 ff 48 8b 7c 24 20 48 83 c7 58 e8 10 bb d9 ff e9 5f fb ff ff 48 c7 c6 80 ce 4c b1 4c 89 ef e8 1c 38 f6 ff <0f> 0b 48 c7 c6 7b c8 4c b1 4c 89 ef e8 0b 38 f6 ff 0f 0b 8b 45 58
  [  793.359732] RSP: 0018:ffffa3ff85ed3d28 EFLAGS: 00010296
  [  793.362367] RAX: 000000000000003a RBX: 0000000000000018 RCX: 0000000000000000
  [  793.365763] RDX: 0000000000000001 RSI: ffffffffb14ac451 RDI: 00000000ffffffff
  [  793.368698] RBP: ffffe93cc535ce40 R08: 0000000000000000 R09: ffffa3ff85ed3ba0
  [  793.370837] R10: 0000000000000003 R11: ffffffffb1d3ed28 R12: 000000000014d739
  [  793.372903] R13: ffffe93cc535ce40 R14: ffffe93cc535ce40 R15: ffffe93cc535ce40
  [  793.374931] FS:  00007f6ccc42a740(0000) GS:ffff8a31bbc00000(0000) knlGS:0000000000000000
  [  793.377136] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  [  793.378656] CR2: 0000561aad6474b2 CR3: 00000001492d4005 CR4: 0000000000170ee0
  [  793.380514] DR0: ffffffffb28ed7d0 DR1: ffffffffb28ed7d1 DR2: ffffffffb28ed7d2
  [  793.382296] DR3: ffffffffb28ed7d3 DR6: 00000000ffff0ff0 DR7: 0000000000000600
  [  793.384028] Call Trace:
  [  793.384655]  <TASK>
  [  793.385210]  ? __lru_add_drain_all+0x164/0x1f0
  [  793.386316]  memory_failure+0x352/0xaa0
  [  793.387249]  ? __pfx_bpf_lsm_capable+0x10/0x10
  [  793.388323]  ? __pfx_security_capable+0x10/0x10
  [  793.389350]  hard_offline_page_store+0x46/0x80
  [  793.390397]  kernfs_fop_write_iter+0x11e/0x200
  [  793.391441]  vfs_write+0x1e4/0x3a0
  [  793.392221]  ksys_write+0x53/0xd0
  [  793.392976]  do_syscall_64+0x3a/0x90
  [  793.393790]  entry_SYSCALL_64_after_hwframe+0x72/0xdc

I'm wondering how this code path is called, one possible path is like this:

  hwpoison_user_mappings
    if PageHuge(hpage) && !PageAnon(hpage)
      try_to_split_huge_mapping()
        find_in_raw_hwp_list
          VM_BUG_ON_PAGE(PageHWPoison(subpage), subpage)

but this looks unlikely because the precheck "PageHuge(hpage) && !PageAnon(hpage)" is
false for anonymous pages.

Another possible code path is:

  hwpoison_user_mappings
    if PageHuge(hpage) && !PageAnon(hpage)
      ...
    else
      try_to_unmap
        rmap_walk
          rmap_walk_anon
            try_to_unmap_one
              if folio_test_hugetlb
                if hgm_eligible
                  find_in_raw_hwp_list
                    VM_BUG_ON_PAGE(PageHWPoison(subpage), subpage)

but this looks also unlikely because of checking folio_test_hugetlb and hgm_eligible
(I think both are false in this testcase.)
Maybe I miss something (and I'll dig this more), but let me share the issue.

Thanks,
Naoya Horiguchi