When enabling the below kernel configs: CONFIG_DEFERRED_STRUCT_PAGE_INIT CONFIG_DEBUG_PAGEALLOC CONFIG_PAGE_EXTENSION CONFIG_DEBUG_VM kernel bootup may fail due to the following oops: BUG: unable to handle kernel NULL pointer dereference at (null) IP: [<ffffffff8118d982>] free_pcppages_bulk+0x2d2/0x8d0 PGD 0 Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC Modules linked in: CPU: 11 PID: 106 Comm: pgdatinit1 Not tainted 4.6.0-rc5-next-20160427 #26 Hardware name: Intel Corporation S5520HC/S5520HC, BIOS S5500.86B.01.10.0025.030220091519 03/02/2009 task: ffff88017c080040 ti: ffff88017c084000 task.ti: ffff88017c084000 RIP: 0010:[<ffffffff8118d982>] [<ffffffff8118d982>] free_pcppages_bulk+0x2d2/0x8d0 RSP: 0000:ffff88017c087c48 EFLAGS: 00010046 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000001 RDX: 0000000000000980 RSI: 0000000000000080 RDI: 0000000000660401 RBP: ffff88017c087cd0 R08: 0000000000000401 R09: 0000000000000009 R10: ffff88017c080040 R11: 000000000000000a R12: 0000000000000400 R13: ffffea0019810000 R14: ffffea0019810040 R15: ffff88066cfe6080 FS: 0000000000000000(0000) GS:ffff88066cd40000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000000 CR3: 0000000002406000 CR4: 00000000000006e0 Stack: ffff88066cd5bbd8 ffff88066cfe6640 0000000000000000 0000000000000000 0000001f0000001f ffff88066cd5bbe8 ffffea0019810000 000000008118f53e 0000000000000009 0000000000000401 ffffffff0000000a 0000000000000001 Call Trace: [<ffffffff8118f602>] free_hot_cold_page+0x192/0x1d0 [<ffffffff8118f69c>] __free_pages+0x5c/0x90 [<ffffffff8262a676>] __free_pages_boot_core+0x11a/0x14e [<ffffffff8262a6fa>] deferred_free_range+0x50/0x62 [<ffffffff8262aa46>] deferred_init_memmap+0x220/0x3c3 [<ffffffff8262a826>] ? setup_per_cpu_pageset+0x35/0x35 [<ffffffff8108b1f8>] kthread+0xf8/0x110 [<ffffffff81c1b732>] ret_from_fork+0x22/0x40 [<ffffffff8108b100>] ? kthread_create_on_node+0x200/0x200 Code: 49 89 d4 48 c1 e0 06 49 01 c5 e9 de fe ff ff 4c 89 f7 44 89 4d b8 4c 89 45 c0 44 89 5d c8 48 89 4d d0 e8 62 c7 07 00 48 8b 4d d0 <48> 8b 00 44 8b 5d c8 4c 8b 45 c0 44 8b 4d b8 a8 02 0f 84 05 ff RIP [<ffffffff8118d982>] free_pcppages_bulk+0x2d2/0x8d0 RSP <ffff88017c087c48> CR2: 0000000000000000 The problem is lookup_page_ext() returns NULL then page_is_guard() tried to access it in page freeing. page_is_guard() depends on PAGE_EXT_DEBUG_GUARD bit of page extension flag, but freeing page might reach here before the page_ext arrays are allocated when feeding a range of pages to the allocator for the first time during bootup or memory hotplug. When it returns NULL, page_is_guard() should just return false instead of checking PAGE_EXT_DEBUG_GUARD unconditionally. Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxx> --- include/linux/mm.h | 3 +++ 1 file changed, 3 insertions(+) diff --git a/include/linux/mm.h b/include/linux/mm.h index 727f7997..b1f2ad1 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2409,6 +2409,9 @@ static inline bool page_is_guard(struct page *page) return false; page_ext = lookup_page_ext(page); + if (unlikely(!page_ext)) + return false; + return test_bit(PAGE_EXT_DEBUG_GUARD, &page_ext->flags); } #else -- 2.0.2 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>