Re: [PATCH] mm: check pfn_valid first in zero_resv_unavail

[Dave Young <dyoung@redhat.com>]

On 11/30/17 at 10:35am, Michal Hocko wrote:
> On Thu 30-11-17 14:04:31, Dave Young wrote:
> > With latest kernel I get below bug while testing kdump:
> > 
> > [    0.000000] BUG: unable to handle kernel paging request at ffffea00034b1040
> > [    0.000000] IP: zero_resv_unavail+0xbd/0x126
> > [    0.000000] PGD 37b98067 P4D 37b98067 PUD 37b97067 PMD 0 
> > [    0.000000] Oops: 0002 [#1] SMP
> > [    0.000000] Modules linked in:
> > [    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.15.0-rc1+ #316
> > [    0.000000] Hardware name: LENOVO 20ARS1BJ02/20ARS1BJ02, BIOS GJET92WW (2.42 ) 03/03/2017
> > [    0.000000] task: ffffffff81a0e4c0 task.stack: ffffffff81a00000
> > [    0.000000] RIP: 0010:zero_resv_unavail+0xbd/0x126
> > [    0.000000] RSP: 0000:ffffffff81a03d88 EFLAGS: 00010006
> > [    0.000000] RAX: 0000000000000000 RBX: ffffea00034b1040 RCX: 0000000000000010
> > [    0.000000] RDX: 0000000000000000 RSI: 0000000000000092 RDI: ffffea00034b1040
> > [    0.000000] RBP: 00000000000d2c41 R08: 00000000000000c0 R09: 0000000000000a0d
> > [    0.000000] R10: 0000000000000002 R11: 0000000000007f01 R12: ffffffff81a03d90
> > [    0.000000] R13: ffffea0000000000 R14: 0000000000000063 R15: 0000000000000062
> > [    0.000000] FS:  0000000000000000(0000) GS:ffffffff81c73000(0000) knlGS:0000000000000000
> > [    0.000000] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [    0.000000] CR2: ffffea00034b1040 CR3: 0000000037609000 CR4: 00000000000606b0
> > [    0.000000] Call Trace:
> > [    0.000000]  ? free_area_init_nodes+0x640/0x664
> > [    0.000000]  ? zone_sizes_init+0x58/0x72
> > [    0.000000]  ? setup_arch+0xb50/0xc6c
> > [    0.000000]  ? start_kernel+0x64/0x43d
> > [    0.000000]  ? secondary_startup_64+0xa5/0xb0
> > [    0.000000] Code: c1 e8 0c 48 39 d8 76 27 48 89 de 48 c1 e3 06 48 c7 c7 7a 87 79 81 e8 b0 c0 3e ff 4c 01 eb b9 10 00 00 00 31 c0 48 89 df 49 ff c6 <f3> ab eb bc 6a 00 49 
> > c7 c0 f0 93 d1 81 31 d2 83 ce ff 41 54 49 
> > [    0.000000] RIP: zero_resv_unavail+0xbd/0x126 RSP: ffffffff81a03d88
> > [    0.000000] CR2: ffffea00034b1040
> > [    0.000000] ---[ end trace f5ba9e8f73c7ee26 ]---
> > 
> > This is introduced with below commit:
> > commit a4a3ede2132ae0863e2d43e06f9b5697c51a7a3b
> > Author: Pavel Tatashin <pasha.tatashin@oracle.com>
> > Date:   Wed Nov 15 17:36:31 2017 -0800
> > 
> >     mm: zero reserved and unavailable struct pages
> 
> the usual format when mentioning a commit is a4a3ede2132a ("mm: zero
> reserved and unavailable struct pages").

Will use the short flavor commit

>  
> > The reason is some efi reserved boot ranges is not reported in E820 ram.
> > In my case it is a bgrt buffer:
> > efi: mem00: [Boot Data          |RUN|  |  |  |  |  |  |   |WB|WT|WC|UC] range=[0x00000000d2c41000-0x00000000d2c85fff] (0MB)
> > 
> > Use "add_efi_memmap" can workaround the problem with another fix:
> > https://lkml.org/lkml/2017/11/30/5
> 
> lkml.org tends to be broken a lot, please use
> http://lkml.kernel.org/r/MSG_ID instead. It would be
> http://lkml.kernel.org/r/20171130052327.GA3500@dhcp-128-65.nay.redhat.com
> here

I also say unstable lkml, but still used to use it since it is simpler
but if you prefer lkml.kernel.org I can change it.

> 
> > In zero_resv_unavail it would be better to check pfn_valid first before zero
> > the page struct. This fixes the problem and potential other similar problems.
> 
> Can we exclude that range from the memblock allocator instead? E.g. what
> happens if somebody allocates from that range?

It is a EFI BGRT image buffer provided by firmware, they are reserved
always and can not be used to allocate memory.

> 
> > Signed-off-by: Dave Young <dyoung@redhat.com>
> > ---
> >  mm/page_alloc.c |    2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > --- linux.orig/mm/page_alloc.c
> > +++ linux/mm/page_alloc.c
> > @@ -6253,6 +6253,8 @@ void __paginginit zero_resv_unavail(void
> >  	pgcnt = 0;
> >  	for_each_resv_unavail_range(i, &start, &end) {
> >  		for (pfn = PFN_DOWN(start); pfn < PFN_UP(end); pfn++) {
> > +			if (!pfn_valid(pfn))
> > +				continue;
> >  			mm_zero_struct_page(pfn_to_page(pfn));
> >  			pgcnt++;
> >  		}
> > 
> > --
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> 
> -- 
> Michal Hocko
> SUSE Labs

Thanks
Dave

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