Re: [PATCH] mm/memory-failure: fix VM_BUG_ON_PAGE(PagePoisoned(page)) when unpoison memory

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On 16.07.24 04:34, Miaohe Lin wrote:
On 2024/7/16 0:16, David Hildenbrand wrote:
On 15.07.24 08:23, Miaohe Lin wrote:
On 2024/7/13 5:09, Andrew Morton wrote:
On Fri, 12 Jul 2024 14:42:49 +0800 Miaohe Lin <linmiaohe@xxxxxxxxxx> wrote:

When I did memory failure tests recently, below panic occurs:

page dumped because: VM_BUG_ON_PAGE(PagePoisoned(page))
kernel BUG at include/linux/page-flags.h:616!
Oops: invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
CPU: 3 PID: 720 Comm: bash Not tainted 6.10.0-rc1-00195-g148743902568 #40
RIP: 0010:unpoison_memory+0x2f3/0x590
RSP: 0018:ffffa57fc8787d60 EFLAGS: 00000246
RAX: 0000000000000037 RBX: 0000000000000009 RCX: ffff9be25fcdc9c8
RDX: 0000000000000000 RSI: 0000000000000027 RDI: ffff9be25fcdc9c0
RBP: 0000000000300000 R08: ffffffffb4956f88 R09: 0000000000009ffb
R10: 0000000000000284 R11: ffffffffb4926fa0 R12: ffffe6b00c000000
R13: ffff9bdb453dfd00 R14: 0000000000000000 R15: fffffffffffffffe
FS:  00007f08f04e4740(0000) GS:ffff9be25fcc0000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000564787a30410 CR3: 000000010d4e2000 CR4: 00000000000006f0
Call Trace:
   <TASK>
   unpoison_memory+0x2f3/0x590
   simple_attr_write_xsigned.constprop.0.isra.0+0xb3/0x110
   debugfs_attr_write+0x42/0x60
   full_proxy_write+0x5b/0x80
   vfs_write+0xd5/0x540
   ksys_write+0x64/0xe0
   do_syscall_64+0xb9/0x1d0
   entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f08f0314887
RSP: 002b:00007ffece710078 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000009 RCX: 00007f08f0314887
RDX: 0000000000000009 RSI: 0000564787a30410 RDI: 0000000000000001
RBP: 0000564787a30410 R08: 000000000000fefe R09: 000000007fffffff
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000009
R13: 00007f08f041b780 R14: 00007f08f0417600 R15: 00007f08f0416a00
   </TASK>
Modules linked in: hwpoison_inject
---[ end trace 0000000000000000 ]---
RIP: 0010:unpoison_memory+0x2f3/0x590
RSP: 0018:ffffa57fc8787d60 EFLAGS: 00000246
RAX: 0000000000000037 RBX: 0000000000000009 RCX: ffff9be25fcdc9c8
RDX: 0000000000000000 RSI: 0000000000000027 RDI: ffff9be25fcdc9c0
RBP: 0000000000300000 R08: ffffffffb4956f88 R09: 0000000000009ffb
R10: 0000000000000284 R11: ffffffffb4926fa0 R12: ffffe6b00c000000
R13: ffff9bdb453dfd00 R14: 0000000000000000 R15: fffffffffffffffe
FS:  00007f08f04e4740(0000) GS:ffff9be25fcc0000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000564787a30410 CR3: 000000010d4e2000 CR4: 00000000000006f0
Kernel panic - not syncing: Fatal exception
Kernel Offset: 0x31c00000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)
---[ end Kernel panic - not syncing: Fatal exception ]---

The root cause is that unpoison_memory() tries to check the PG_HWPoison
flags of an uninitialized page. So VM_BUG_ON_PAGE(PagePoisoned(page)) is
triggered.

I'm not seeing the call path.  Is this BUG happening via

static __always_inline void __ClearPage##uname(struct page *page)    \
{                                    \
     VM_BUG_ON_PAGE(!Page##uname(page), page);            \
     page->page_type |= PG_##lname;                    \
}

?

If so, where's the callsite?

It is BUG on PF_ANY():

PAGEFLAG(HWPoison, hwpoison, PF_ANY)

#define PF_ANY(page, enforce)    PF_POISONED_CHECK(page)

#define PF_POISONED_CHECK(page) ({                    \
     VM_BUG_ON_PGFLAGS(PagePoisoned(page), page);        \
     page; })

#define    PAGE_POISON_PATTERN    -1l
static inline int PagePoisoned(const struct page *page)
{
     return READ_ONCE(page->flags) == PAGE_POISON_PATTERN;
}

The offlined pages will have page->flags set to PAGE_POISON_PATTERN while pfn is still valid:

offline_pages
    remove_pfn_range_from_zone
      page_init_poison
        memset(page, PAGE_POISON_PATTERN, size);

Worth noting that this happens after __offline_isolated_pages() marked the covering sections as offline.

Are we missing a pfn_to_online_page() check somewhere, or are we racing with offlining code that marks the section offline?

I was thinking about to use pfn_to_online_page() instead of pfn_to_page() in unpoison_memory() so we can get rid of offlined pages.
But there're ZONE_DEVICE pages. They're not-onlined too. And unpoison_memory() should work for them. So we can't simply use
pfn_to_online_page() in that. Or am I miss something?

Right, pfn_to_online_page() does not detect ZONE_DEVICE. That has to be handled separately if pfn_to_online_page() would fail.

... which is what we do in memory_failure():

p = pfn_to_online_page(pfn);
if (!p) {
	if (pfn_valid(pfn)) {
		pgmap = get_dev_pagemap(pfn, NULL);
		put_ref_page(pfn, flags);
		if (pgmap) {
			...
		}
	}
	...
}

--
Cheers,

David / dhildenb





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