linux-kernel - Re: [mm] BUG: Int 6: CR2 (null)

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Date:	Thu, 23 Oct 2014 14:03:43 +0800
From:	Weijie Yang <weijie.yang.kh@...il.com>
To:	Fengguang Wu <fengguang.wu@...el.com>
Cc:	Marek Szyprowski <m.szyprowski@...sung.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	LKML <linux-kernel@...r.kernel.org>, lkp@...org,
	mina86@...a86.com, Joonsoo Kim <iamjoonsoo.kim@....com>,
	Linux-MM <linux-mm@...ck.org>
Subject: Re: [mm] BUG: Int 6: CR2 (null)

On Thu, Oct 9, 2014 at 10:04 AM, Fengguang Wu <fengguang.wu@...el.com> wrote:
> Hi Marek,
>
> FYI, we noticed the below changes on
>
> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> commit 478e86d7c8c5f41e29abb81b05b459d24bdc71a2 ("mm: cma: adjust address limit to avoid hitting low/high memory boundary")
>
>
> +------------------------------------------+------------+------------+
> |                                          | 81febe58a8 | 478e86d7c8 |
> +------------------------------------------+------------+------------+
> | boot_successes                           | 10         | 0          |
> | boot_failures                            | 5          | 10         |
> | kernel_BUG_at_arch/x86/mm/physaddr.c     | 5          |            |
> | invalid_opcode                           | 5          |            |
> | EIP_is_at__phys_addr                     | 5          |            |
> | Kernel_panic-not_syncing:Fatal_exception | 5          |            |
> | backtrace:vm_mmap_pgoff                  | 5          |            |
> | backtrace:SyS_mmap_pgoff                 | 5          |            |
> | BUG:Int_CR2(null)                        | 0          | 10         |
> +------------------------------------------+------------+------------+
>
> [    0.000000] BRK [0x025ee000, 0x025eefff] PGTABLE
> [    0.000000] cma: dma_contiguous_reserve(limit 13ffe000)
> [    0.000000] cma: dma_contiguous_reserve: reserving 31 MiB for global area
> [    0.000000] BUG: Int 6: CR2   (null)
> [    0.000000]      EDI c0000000  ESI   (null)  EBP 41c11ea4  EBX 425cc101
> [    0.000000]      ESP 41c11e98   ES 0000007b   DS 0000007b
> [    0.000000]      EDX 00000001  ECX   (null)  EAX 41cd8150
> [    0.000000]      vec 00000006  err   (null)  EIP 41072227   CS 00000060  flg 00210002
> [    0.000000] Stack: 425cc150   (null)   (null) 41c11ef4 41d4ee4d   (null) 13ffe000 41c11ec4
> [    0.000000]        41c2d900   (null) 13ffe000   (null) 4185793e 0000002e 410c2982 41c11f00
> [    0.000000]        410c2df5   (null)   (null)   (null) 425cc150 00013efe   (null) 41c11f28
> [    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 3.17.0-next-20141008 #815
> [    0.000000]  00000000 425cc101 41c11e48 41850786 41c11ea4 41d2b1db 41d95f71 00000006
> [    0.000000]  00000000 c0000000 00000000 41c11ea4 425cc101 41c11e98 0000007b 0000007b
> [    0.000000]  00000001 00000000 41cd8150 00000006 00000000 41072227 00000060 00210002
> [    0.000000] Call Trace:
> [    0.000000]  [<41850786>] dump_stack+0x16/0x18
> [    0.000000]  [<41d2b1db>] early_idt_handler+0x6b/0x6b
> [    0.000000]  [<41072227>] ? __phys_addr+0x2e/0xca
> [    0.000000]  [<41d4ee4d>] cma_declare_contiguous+0x3c/0x2d7
> [    0.000000]  [<4185793e>] ? _raw_spin_unlock_irqrestore+0x59/0x91
> [    0.000000]  [<410c2982>] ? wake_up_klogd+0x8/0x33
> [    0.000000]  [<410c2df5>] ? console_unlock+0x448/0x461
> [    0.000000]  [<41d6d359>] dma_contiguous_reserve_area+0x27/0x47
> [    0.000000]  [<41d6d4d1>] dma_contiguous_reserve+0x158/0x163
> [    0.000000]  [<41d33e0f>] setup_arch+0x79b/0xc68
> [    0.000000]  [<4184c0b4>] ? printk+0x1c/0x1e
> [    0.000000]  [<41d2b7cf>] start_kernel+0x9c/0x456
> [    0.000000]  [<41d2b2ca>] i386_start_kernel+0x79/0x7d
>

I notice that code has been merged into mainline kernel without fix,
maybe fengguang's mail was missed.

I review the code, dma_contiguous_reserve() is called before initmem_init(),
so the variable high_memory is not initialized and calculated by
__pa(high_memory),
in x86 arch high_memory is initialized after dma_contiguous_reserve(), while
in arm arch high_memory is initialized before dma_contiguous_reserve(),
I think that is the reason which causes the BUG in x86.

However, I'm not familiar with system init sequence, so I send this
notice mail rather than a patch :-(

cc more people

>
> Thanks,
> Fengguang
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