Re: [PATCH -next] mm/hwpoison: clear MF_COUNT_INCREASED before retrying get_any_page()
From: Liu Shixin <hidden>
Date: 2021-12-22 01:49:22
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On 2021/12/22 8:37, Naoya Horiguchi wrote:
On Tue, Dec 21, 2021 at 03:49:08PM +0800, Liu Shixin wrote:quoted
Hulk Robot reported a panic in put_page_testzero() when testing madvise() with MADV_SOFT_OFFLINE. The BUG() is triggered when retrying get_any_page(). This is because we keep MF_COUNT_INCREASED flag in second try but the refcnt is not increased.Hi Shixin, Thanks you for the report. I'm not still sure about the logic behind the bug. madvise(MADV_SOFT_OFFLINE) should not work on free pages because madvise_inject_error() pins the target page with get_user_pages_fast() (MF_COUNT_INCREASED means refcount is incremented by the caller). The retry logic can be called when soft_offline_free_page() fails, so the logic assumes that the target page is a free page. So why does clearing MF_COUNT_INCREASED affect and solve the issue? It seems to me that if soft_offline_page() is called on a free page with MF_COUNT_INCREASED set, then it's problematic itself. Thanks, Naoya Horiguchi
The page is not free when soft_offline_page() is called. In get_any_page(), if MF_COUNT_INCREASED is set and !HWPoisonHandlable(page), put_page() will be called firstly and then goto try_again. The page is freed in this period. Thanks, Liu Shixin
quoted
page dumped because: VM_BUG_ON_PAGE(page_ref_count(page) == 0) ------------[ cut here ]------------ kernel BUG at include/linux/mm.h:737! invalid opcode: 0000 [#1] PREEMPT SMP CPU: 5 PID: 2135 Comm: sshd Tainted: G B 5.16.0-rc6-dirty #373 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014 RIP: 0010:release_pages+0x53f/0x840 Code: 0c 01 4c 8d 60 ff e9 5b fb ff ff 48 c7 c6 d8 97 0c b3 4c 89 e7 48 83 05 0e 7b 3c 0c 01 e8 89 3d 04 00 48 83 05 11 7b 3c 0c 01 <0f> 0b 48 83 05 0f 7b 3c 0c 01 48 83 05 0f 7b 3c 0c 01 48 83 05f RSP: 0018:ffffc900015a7bc0 EFLAGS: 00010002 RAX: 000000000000003e RBX: ffffffffbace04c8 RCX: 0000000000000002 RDX: 0000000000000000 RSI: 0000000000000001 RDI: 00000000ffffffff RBP: ffff88817b9acd50 R08: 0000000000000000 R09: c0000000ffefffff R10: 0000000000000001 R11: ffffc900015a79b0 R12: ffffea0005e1c900 R13: ffffea0005e1de88 R14: 000000000000001f R15: ffff888100071000 FS: 0000000000000000(0000) GS:ffff88842fb40000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f305e8de3d4 CR3: 000000017bb6f000 CR4: 00000000000006e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <TASK> free_pages_and_swap_cache+0x64/0x80 tlb_flush_mmu+0x6f/0x220 unmap_page_range+0xe6c/0x12c0 unmap_single_vma+0x90/0x170 unmap_vmas+0xc4/0x180 exit_mmap+0xde/0x3a0 mmput+0xa3/0x250 do_exit+0x564/0x1470 do_group_exit+0x3b/0x100 __do_sys_exit_group+0x13/0x20 __x64_sys_exit_group+0x16/0x20 do_syscall_64+0x34/0x80 entry_SYSCALL_64_after_hwframe+0x44/0xae RIP: 0033:0x7f30625401d9 Code: Unable to access opcode bytes at RIP 0x7f30625401af. RSP: 002b:00007ffe391b0c88 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7 RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007f30625401d9 RDX: 0000000000000001 RSI: 0000000000000000 RDI: 0000000000000001 RBP: 00007f306283d838 R08: 000000000000003c R09: 00000000000000e7 R10: fffffffffffffe30 R11: 0000000000000246 R12: 00007f306283d838 R13: 00007f3062842e80 R14: 0000000000000000 R15: ffffaa4fb7932430 </TASK> Modules linked in: ---[ end trace e99579b570fe0649 ]--- RIP: 0010:release_pages+0x53f/0x840 Code: 0c 01 4c 8d 60 ff e9 5b fb ff ff 48 c7 c6 d8 97 0c b3 4c 89 e7 48 83 05 0e 7b 3c 0c 01 e8 89 3d 04 00 48 83 05 11 7b 3c 0c 01 <0f> 0b 48 83 05 0f 7b 3c 0c 01 48 83 05 0f 7b 3c 0c 01 48 83 05f RSP: 0018:ffffc900015a7bc0 EFLAGS: 00010002 RAX: 000000000000003e RBX: ffffffffbace04c8 RCX: 0000000000000002 RDX: 0000000000000000 RSI: 0000000000000001 RDI: 00000000ffffffff RBP: ffff88817b9acd50 R08: 0000000000000000 R09: c0000000ffefffff R10: 0000000000000001 R11: ffffc900015a79b0 R12: ffffea0005e1c900 R13: ffffea0005e1de88 R14: 000000000000001f R15: ffff888100071000 FS: 0000000000000000(0000) GS:ffff88842fb40000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f305e8de3d4 CR3: 000000017bb6f000 CR4: 00000000000006e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Fixes: b94e02822deb ("mm,hwpoison: try to narrow window race for free pages") Reported-by: Hulk Robot <redacted> Signed-off-by: Liu Shixin <redacted> --- mm/memory-failure.c | 1 + 1 file changed, 1 insertion(+)diff --git a/mm/memory-failure.c b/mm/memory-failure.c index 68d9a35f8908..160526f83bcb 100644 --- a/mm/memory-failure.c +++ b/mm/memory-failure.c@@ -2288,6 +2288,7 @@ int soft_offline_page(unsigned long pfn, int flags) } else if (ret == 0) { if (soft_offline_free_page(page) && try_again) { try_again = false; + flags &= ~MF_COUNT_INCREASED; goto retry; } }-- 2.25.1.