Re: [PATCH v1] mm: relax deferred struct page requirements

[Jiri Slaby]

On 08/31/2018, 02:10 PM, Pasha Tatashin wrote:
> Thanks Jiri, I am now able to reproduce it with your new config.
> 
> I have tried yesterday to enable sparsemem and deferred_struct_init on
> x86_32, and that kernel booted fine, there must be something else in
> your config that helps to trigger this problem. I am studying it now.
> 
> [    0.051245] Initializing CPU#0
> [    0.051682] Initializing HighMem for node 0 (000367fe:0007ffe0)
> [    0.067499] BUG: unable to handle kernel NULL pointer dereference at
> 00000028
> [    0.068452] *pdpt = 0000000000000000 *pde = f000ff53f000ff53
> [    0.069105] Oops: 0000 [#1] PREEMPT SMP PTI
> [    0.069595] CPU: 0 PID: 0 Comm: swapper Not tainted
> 4.19.0-rc1-pae_pt_jiri #1
> [    0.070382] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> BIOS 1.11.0-20171110_100015-anatol 04/01/2014
> [    0.071545] EIP: free_unref_page_prepare.part.70+0x2c/0x50
> [    0.072178] Code: 19 e9 ff 89 d1 55 c1 ea 11 c1 e9 07 8b 14 d5 44 52
> fd d6 81 e1 fc 03 00 00 89 e5 56 53 89 cb be 1d 00 00 00 c1 eb 05 83 e1
> 1f <8b> 14 9a 29 ce 89 f1 d3 ea 83 e2 07 89 50 10 b8 01 00 00 00 5b 5e
> [    0.074296] EAX: f4cfa000 EBX: 0000000a ECX: 00000010 EDX: 00000000
> [    0.075005] ESI: 0000001d EDI: 0007ffe0 EBP: d6d41ed0 ESP: d6d41ec8
> [    0.075714] DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068 EFLAGS: 00210002
> [    0.076508] CR0: 80050033 CR2: 00000028 CR3: 16f20000 CR4: 000406b0
> [    0.077242] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
> [    0.077934] DR6: fffe0ff0 DR7: 00000400
> [    0.078380] Call Trace:
> [    0.078670]  free_unref_page+0x3a/0x90
> [    0.079136]  __free_pages+0x25/0x30
> [    0.079533]  free_highmem_page+0x1e/0x50
> [    0.079978]  add_highpages_with_active_regions+0xd1/0x11f
> [    0.080592]  set_highmem_pages_init+0x67/0x7d
> [    0.081076]  mem_init+0x30/0x1fc

page_to_pfn(pfn_to_page(pfn)) != pfn with my .config on pfns >= 0x60000:

[    0.157667] add_highpages_with_active_regions: pfn=5fffb pg=f55f9f4c
pfn(pg(pfn)=5fffb sec=2
[    0.159231] add_highpages_with_active_regions: pfn=5fffc pg=f55f9f70
pfn(pg(pfn)=5fffc sec=2
[    0.161020] add_highpages_with_active_regions: pfn=5fffd pg=f55f9f94
pfn(pg(pfn)=5fffd sec=2
[    0.163149] add_highpages_with_active_regions: pfn=5fffe pg=f55f9fb8
pfn(pg(pfn)=5fffe sec=2
[    0.165204] add_highpages_with_active_regions: pfn=5ffff pg=f55f9fdc
pfn(pg(pfn)=5ffff sec=2
[    0.167216] add_highpages_with_active_regions: pfn=60000 pg=f4cfa000
pfn(pg(pfn)=c716a800 sec=3

So add_highpages_with_active_regions passes down page to
free_highmem_page and later, free_unref_page does page_to_pfn(page) and
__get_pfnblock_flags_mask operates on this modified pfn leading to crash
â __pfn_to_section(pfn)->pageblock_flags is NULL!

Note that __pfn_to_section(pfn)->pageblock_flags on the original pfn
returns a valid bitmap.

thanks,
-- 
js
suse labs