linux-kernel - [PATCH 0/2] liveupdate: Fix boot failure due to kmemleak access to unmapped pages

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Message-ID: <20251120144147.90508-1-ranxiaokai627@163.com>
Date: Thu, 20 Nov 2025 14:41:45 +0000
From: ranxiaokai627@....com
To: catalin.marinas@....com,
	akpm@...ux-foundation.org,
	graf@...zon.com,
	rppt@...nel.org,
	pasha.tatashin@...een.com,
	pratyush@...nel.org,
	changyuanl@...gle.com
Cc: linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	kexec@...ts.infradead.org,
	ran.xiaokai@....com.cn,
	ranxiaokai627@....com
Subject: [PATCH 0/2] liveupdate: Fix boot failure due to kmemleak access to unmapped pages

From: Ran Xiaokai <ran.xiaokai@....com.cn>

When booting with debug_pagealloc=on while having:
CONFIG_KEXEC_HANDOVER_ENABLE_DEFAULT=y  
CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=n  
the system fails to boot due to page faults during kmemleak scanning.

Crash logs:
BUG: unable to handle page fault for address: ffff8880cd400000
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 11de00067 P4D 11de00067 PUD 11af2b067 PMD 11aec1067 PTE 800fffff32bff020
Oops: Oops: 0000 [#1] SMP DEBUG_PAGEALLOC
RIP: 0010:scan_block+0x43/0xb0
Call Trace:
 <TASK>
 scan_gray_list+0x2b5/0x2f0
 kmemleak_scan+0x3b1/0xcf0
 kmemleak_scan_thread+0x7d/0xc0
 kthread+0x11c/0x240
 ret_from_fork+0x2d3/0x370
 ret_from_fork_asm+0x11/0x20
 </TASK>

This occurs because:
With debug_pagealloc enabled, __free_pages() invokes
debug_pagealloc_unmap_pages(), clearing the _PAGE_PRESENT bit for
freed pages in the direct mapping.
Commit 3dc92c311498 ("kexec: add Kexec HandOver (KHO) generation helpers")
releases the KHO scratch region via init_cma_reserved_pageblock(),
unmapping its physical pages. Subsequent kmemleak scanning accesses
these unmapped pages, triggering fatal page faults.

This patch introduces kmemleak_no_scan_phys(phys_addr_t),
a physical-address variant of kmemleak_no_scan(), which marks
memblock regions as OBJECT_NO_SCAN.

We invoke this from kho_reserve_scratch() to exclude the reserved
region from scanning before it is released to the buddy allocator.

This is based linux next-20251119.

Ran Xiaokai (2):
  mm: kmemleak: introduce kmemleak_no_scan_phys() helper
  liveupdate: Fix boot failure due to kmemleak access to unmapped pages

 include/linux/kmemleak.h           |  4 ++++
 kernel/liveupdate/kexec_handover.c |  4 ++++
 mm/kmemleak.c                      | 15 ++++++++++++---
 3 files changed, 20 insertions(+), 3 deletions(-)

-- 
2.25.1