Re: [RFC PATCH v1 4/7] mm/memory_failure: unmap raw HWPoison PTEs when possible
From: HORIGUCHI NAOYA(堀口 直也)
Date: Mon May 29 2023 - 22:25:30 EST
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@xxxxxxxxxx>
> ---
...
> @@ -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