linux-kernel - Re: [RFC PATCH] driver: base: memory: Maintain correct mem->end_section

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Date:	Fri, 14 Aug 2015 10:27:53 -0500
From:	Nathan Fontenot <nfont@...ux.vnet.ibm.com>
To:	Bharata B Rao <bharata@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
CC:	david@...son.dropbear.id.au
Subject: Re: [RFC PATCH] driver: base: memory: Maintain correct mem->end_section_nr
 when memory block is partially filled

On 08/13/2015 04:17 AM, Bharata B Rao wrote:
> Last section of memory block is always initialized to
> 
> mem->start_section_nr + sections_per_block - 1
> 
> which will not be true for a section that doesn't contain sections_per_block
> sections due to the memory size specified. This causes the following
> kernel crash when memory blocks under a node are registered during reboot
> that follows a memory hotplug operation on pseries guest.
> 
> Unable to handle kernel paging request for data at address 0xf0000000003f0020
> Faulting instruction address: 0xc0000000007657cc
> Oops: Kernel access of bad area, sig: 11 [#1]
> SMP NR_CPUS=1024 NUMA pSeries
> 
> Modules linked in:
> 
> CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.2.0-rc6+ #48
> task: c0000000ba3c0000 ti: c00000013c580000 task.ti: c00000013c580000
> NIP: c0000000007657cc LR: c000000000592dbc CTR: 0000000000000400
> REGS: c00000013c5836f0 TRAP: 0300   Not tainted  (4.2.0-rc6+)
> MSR: 8000000000009032  MSR: 8000000000009032 <<SFSF,EE,EE,ME,ME,IR,IR,DR,DR,RI,RI>>  CR: 48000048  XER: 00000000
>   CR: 48000048  XER: 00000000
> CFAR: 00003fff990f50ec CFAR: 00003fff990f50ec DAR: f0000000003f0020 DSISR: 40000000 DAR: f0000000003f0020 DSISR: 40000000 SOFTE: 1 SOFTE: 1
> GPR00: c000000000592dbc c000000000592dbc c00000013c583970 c00000013c583970 c0000000014f0300 c0000000014f0300 00000000003f0000 00000000003f0000
> GPR04: 0000000000000000 0000000000000000 c0000000f43b2900 c0000000f43b2900 c0000000ba324668 c0000000ba324668 0000000000000001 0000000000000001
> GPR08: c000000001540300 c000000001540300 f000000000000000 f000000000000000 f0000000003f0000 f0000000003f0000 0000000000000001 0000000000000001
> GPR12: 0000000024000084 0000000024000084 c00000000ff20000 c00000000ff20000 c00000000000b5b0 c00000000000b5b0 0000000000000000 0000000000000000
> GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 0000000000000000 0000000000000000 0000000000000000 0000000000000000
> GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 0000000000000000 0000000000000000 0000000000000000 0000000000000000
> GPR24: c00000000188c380 c00000000188c380 0000000000000000 0000000000000000 0000000000014000 0000000000014000 c0000000018b54e8 c0000000018b54e8
> GPR28: c00000013c06e800 c00000013c06e800 000000000000ffff 000000000000ffff 0000000000000000 0000000000000000 000000000000fc00 000000000000fc00
> 
> NIP [c0000000007657cc] .get_nid_for_pfn+0x2c/0x60
> LR [c000000000592dbc] .register_mem_sect_under_node+0x8c/0x150
> Call Trace:
> [c00000013c583970] [c00000000056e44c] .put_device+0x2c/0x50
> [c00000013c5839f0] [c000000000592dbc] .register_mem_sect_under_node+0x8c/0x150
> [c00000013c583a80] [c0000000005932b4] .register_one_node+0x2c4/0x380
> [c00000013c583b30] [c000000000c882b8] .topology_init+0x44/0x1e0
> [c00000013c583bf0] [c00000000000ad30] .do_one_initcall+0x110/0x270
> [c00000013c583ce0] [c000000000c845d4] .kernel_init_freeable+0x278/0x360
> [c00000013c583db0] [c00000000000b5d4] .kernel_init+0x24/0x130
> [c00000013c583e30] [c0000000000094e8] .ret_from_kernel_thread+0x58/0x70
> 
> Fix this by updating the memory block to always contain the right
> number of sections instead of assuming sections_per_block.
> 
> Signed-off-by: Bharata B Rao <bharata@...ux.vnet.ibm.com>
> Cc: Nathan Fontenot <nfont@...ux.vnet.ibm.com>
> ---
>  drivers/base/memory.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 2804aed..7f3ce2e 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -645,6 +645,7 @@ static int add_memory_block(int base_section_nr)
>  	if (ret)
>  		return ret;
>  	mem->section_count = section_count;
> +        mem->end_section_nr = mem->start_section_nr + section_count -1;

I think this change may be correct but makes me wonder if we need to update
code elsewhere. There are places (at least in drivers/base/memory.c) that assume
a memory block contains sections_per_block sections.

Also, I think you may need to cc GregKH for this patch.

-Nathan
 
>  	return 0;
>  }
> 

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