linux-kernel - [PATCH -rc7] mm/huge_memory: mark huge_zero

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Date: Sat, 11 May 2024 11:54:35 +0800
From: Miaohe Lin <linmiaohe@...wei.com>
To: <akpm@...ux-foundation.org>
CC: <shy828301@...il.com>, <nao.horiguchi@...il.com>,
	<xuyu@...ux.alibaba.com>, <linmiaohe@...wei.com>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>
Subject: [PATCH -rc7] mm/huge_memory: mark huge_zero_page reserved

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_page
without increasing the page refcnt. But then unpoison_memory() will
decrease the page refcnt unexpectly as it appears like a successfully
hwpoisoned page leading to VM_BUG_ON_PAGE(page_ref_count(page) == 0)
when releasing huge_zero_page.

Fix this issue by marking huge_zero_page 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@...wei.com>
Cc: <stable@...r.kernel.org>
---
 mm/huge_memory.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 89f58c7603b2..a605bc0437cd 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -208,6 +208,7 @@ static bool get_huge_zero_page(void)
 		__free_pages(zero_page, compound_order(zero_page));
 		goto retry;
 	}
+	__SetPageReserved(zero_page);
 	WRITE_ONCE(huge_zero_pfn, page_to_pfn(zero_page));
 
 	/* We take additional reference here. It will be put back by shrinker */
@@ -260,6 +261,7 @@ static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink,
 		struct page *zero_page = xchg(&huge_zero_page, NULL);
 		BUG_ON(zero_page == NULL);
 		WRITE_ONCE(huge_zero_pfn, ~0UL);
+		__ClearPageReserved(zero_page);
 		__free_pages(zero_page, compound_order(zero_page));
 		return HPAGE_PMD_NR;
 	}
-- 
2.33.0