Re: [PATCH] mm/huge_memory: mark huge_zero_folio reserved

[David Hildenbrand]

On 11.05.24 05:28, Miaohe Lin wrote:
> When I did memory failure tests recently, below panic occurs:
>
>   kernel BUG at include/linux/mm.h:1135!
>   invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
>   CPU: 9 PID: 137 Comm: kswapd1 Not tainted 6.9.0-rc4-00491-gd5ce28f156fe-dirty #14
>   RIP: 0010:shrink_huge_zero_page_scan+0x168/0x1a0
>   RSP: 0018:ffff9933c6c57bd0 EFLAGS: 00000246
>   RAX: 000000000000003e RBX: 0000000000000000 RCX: ffff88f61fc5c9c8
>   RDX: 0000000000000000 RSI: 0000000000000027 RDI: ffff88f61fc5c9c0
>   RBP: ffffcd7c446b0000 R08: ffffffff9a9405f0 R09: 0000000000005492
>   R10: 00000000000030ea R11: ffffffff9a9405f0 R12: 0000000000000000
>   R13: 0000000000000000 R14: 0000000000000000 R15: ffff88e703c4ac00
>   FS:  0000000000000000(0000) GS:ffff88f61fc40000(0000) knlGS:0000000000000000
>   CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>   CR2: 000055f4da6e9878 CR3: 0000000c71048000 CR4: 00000000000006f0
>   Call Trace:
>    <TASK>
>    do_shrink_slab+0x14f/0x6a0
>    shrink_slab+0xca/0x8c0
>    shrink_node+0x2d0/0x7d0
>    balance_pgdat+0x33a/0x720
>    kswapd+0x1f3/0x410
>    kthread+0xd5/0x100
>    ret_from_fork+0x2f/0x50
>    ret_from_fork_asm+0x1a/0x30
>    </TASK>
>   Modules linked in: mce_inject hwpoison_inject
>   ---[ end trace 0000000000000000 ]---
>   RIP: 0010:shrink_huge_zero_page_scan+0x168/0x1a0
>   RSP: 0018:ffff9933c6c57bd0 EFLAGS: 00000246
>   RAX: 000000000000003e RBX: 0000000000000000 RCX: ffff88f61fc5c9c8
>   RDX: 0000000000000000 RSI: 0000000000000027 RDI: ffff88f61fc5c9c0
>   RBP: ffffcd7c446b0000 R08: ffffffff9a9405f0 R09: 0000000000005492
>   R10: 00000000000030ea R11: ffffffff9a9405f0 R12: 0000000000000000
>   R13: 0000000000000000 R14: 0000000000000000 R15: ffff88e703c4ac00
>   FS:  0000000000000000(0000) GS:ffff88f61fc40000(0000) knlGS:0000000000000000
>   CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>   CR2: 000055f4da6e9878 CR3: 0000000c71048000 CR4: 00000000000006f0
>
> The root cause is that HWPoison flag will be set for huge_zero_folio
> without increasing the folio refcnt. But then unpoison_memory() will
> decrease the folio refcnt unexpectly as it appears like a successfully
> hwpoisoned folio leading to VM_BUG_ON_PAGE(page_ref_count(page) == 0)
> when releasing huge_zero_folio.
>
> Fix this issue by marking huge_zero_folio reserved. So unpoison_memory()
> will skip this page. This will make it consistent with ZERO_PAGE case too.
>
> Fixes: 478d134e9506 ("mm/huge_memory: do not overkill when splitting huge_zero_page")
> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> ---
>   mm/huge_memory.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 317de2afd371..d508ff793145 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -212,6 +212,7 @@ static bool get_huge_zero_page(void)
>   		folio_put(zero_folio);
>   		goto retry;
>   	}
> +	__folio_set_reserved(zero_folio);

We want to limit/remove the use of PG_reserve. Please find a different 
way (e.g., simply checking for the huge zero page directly).

--
Cheers,

David / dhildenb