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

[Michal Hocko]

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@xxxxxxxxxx>
> 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").
 
> 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@xxxxxxxxxxxxxxxxxxxxxxxxxx
here

> 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?

> Signed-off-by: Dave Young <dyoung@xxxxxxxxxx>
> ---
>  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