The patch titled Subject: mm/huge_memory: mark huge_zero_page reserved has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-huge_memory-mark-huge_zero_page-reserved.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Miaohe Lin linmiaohe@huawei.com Subject: mm/huge_memory: mark huge_zero_page reserved Date: Sat, 11 May 2024 11:54:35 +0800

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.

Link: https://lkml.kernel.org/r/20240511035435.1477004-1-linmiaohe@huawei.com Fixes: 478d134e9506 ("mm/huge_memory: do not overkill when splitting huge_zero_page") Signed-off-by: Miaohe Lin linmiaohe@huawei.com Cc: Naoya Horiguchi nao.horiguchi@gmail.com Cc: Xu Yu xuyu@linux.alibaba.com Cc: Yang Shi shy828301@gmail.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/huge_memory.c | 2 ++ 1 file changed, 2 insertions(+)

--- a/mm/huge_memory.c~mm-huge_memory-mark-huge_zero_page-reserved +++ a/mm/huge_memory.c @@ -208,6 +208,7 @@ retry: __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_pa 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; } _

Patches currently in -mm which might be from linmiaohe@huawei.com are

mm-huge_memory-mark-huge_zero_page-reserved.patch