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

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Date:	Mon, 17 Aug 2015 09:32:50 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Bharata B Rao <bharata@...ux.vnet.ibm.com>
Cc:	Nathan Fontenot <nfont@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, 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 Mon, Aug 17, 2015 at 11:56:53AM +0530, Bharata B Rao wrote:
> On Fri, Aug 14, 2015 at 10:27:53AM -0500, Nathan Fontenot wrote:
> > 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.
>  
> Hi Greg - Do you think the above is the right fix to the problem that is
> described here ?

I have no idea, sorry, I didn't write this code :)
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