Re: [PATCH v6 04/10] mm/memory_hotplug: Don't access uninitialized memmaps in shrink_zone_span()

David Hildenbrand
2019-11-19T14:16:22Z

On 14.10.19 21:17, Andrew Morton wrote:
> On Mon, 14 Oct 2019 11:32:13 +0200 David Hildenbrand <david@redhat.com> wrote:
>
>>> Fixes: d0dc12e86b31 ("mm/memory_hotplug: optimize memory hotplug")
>>
>> @Andrew, can you convert that to
>>
>> Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded
>> memory to zones until online") # visible after d0dc12e86b319
>>
>> and add
>>
>> Cc: stable@vger.kernel.org # v4.13+
>
> Done, thanks.
>

Just a note that Toshiki reported a BUG (race between delayed
initialization of ZONE_DEVICE memmaps without holding the memory
hotplug lock and concurrent zone shrinking).

https://lkml.org/lkml/2019/11/14/1040

"Iteration of create and destroy namespace causes the panic as below:

[ 41.207694] kernel BUG at mm/page_alloc.c:535!
[ 41.208109] invalid opcode: 0000 [#1] SMP PTI
[ 41.208508] CPU: 7 PID: 2766 Comm: ndctl Not tainted 5.4.0-rc4 #6
[ 41.209064] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.11.0-0-g63451fca13-prebuilt.qemu-project.org 04/01/2014
[ 41.210175] RIP: 0010:set_pfnblock_flags_mask+0x95/0xf0
[ 41.210643] Code: 04 41 83 e2 3c 48 8d 04 a8 48 c1 e0 07 48 03 04 dd e0 59 55 bb 48 8b 58 68 48 39 da 73 0e 48 c7 c6 70 ac 11 bb e8 1b b2 fd ff <0f> 0b 48 03 58 78 48 39 da 73 e9 49 01 ca b9 3f 00 00 00 4f 8d 0c
[ 41.212354] RSP: 0018:ffffac0d41557c80 EFLAGS: 00010246
[ 41.212821] RAX: 000000000000004a RBX: 0000000000244a00 RCX: 0000000000000000
[ 41.213459] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffffbb1197dc
[ 41.214100] RBP: 000000000000000c R08: 0000000000000439 R09: 0000000000000059
[ 41.214736] R10: 0000000000000000 R11: ffffac0d41557b08 R12: ffff8be475ea72b0
[ 41.215376] R13: 000000000000fa00 R14: 0000000000250000 R15: 00000000fffc0bb5
[ 41.216008] FS: 00007f30862ab600(0000) GS:ffff8be57bc40000(0000) knlGS:0000000000000000
[ 41.216771] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 41.217299] CR2: 000055e824d0d508 CR3: 0000000231dac000 CR4: 00000000000006e0
[ 41.217934] Call Trace:
[ 41.218225] memmap_init_zone_device+0x165/0x17c
[ 41.218642] memremap_pages+0x4c1/0x540
[ 41.218989] devm_memremap_pages+0x1d/0x60
[ 41.219367] pmem_attach_disk+0x16b/0x600 [nd_pmem]
[ 41.219804] ? devm_nsio_enable+0xb8/0xe0
[ 41.220172] nvdimm_bus_probe+0x69/0x1c0
[ 41.220526] really_probe+0x1c2/0x3e0
[ 41.220856] driver_probe_device+0xb4/0x100
[ 41.221238] device_driver_attach+0x4f/0x60
[ 41.221611] bind_store+0xc9/0x110
[ 41.221919] kernfs_fop_write+0x116/0x190
[ 41.222326] vfs_write+0xa5/0x1a0
[ 41.222626] ksys_write+0x59/0xd0
[ 41.222927] do_syscall_64+0x5b/0x180
[ 41.223264] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 41.223714] RIP: 0033:0x7f30865d0ed8
[ 41.224037] Code: 89 02 48 c7 c0 ff ff ff ff eb b3 0f 1f 80 00 00 00 00 f3 0f 1e fa 48 8d 05 45 78 0d 00 8b 00 85 c0 75 17 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 58 c3 0f 1f 80 00 00 00 00 41 54 49 89 d4 55
[ 41.225920] RSP: 002b:00007fffe5d30a78 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[ 41.226608] RAX: ffffffffffffffda RBX: 000055e824d07f40 RCX: 00007f30865d0ed8
[ 41.227242] RDX: 0000000000000007 RSI: 000055e824d07f40 RDI: 0000000000000004
[ 41.227870] RBP: 0000000000000007 R08: 0000000000000007 R09: 0000000000000006
[ 41.228753] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000004
[ 41.229419] R13: 00007f30862ab528 R14: 0000000000000001 R15: 000055e824d07f40

While creating a namespace and initializing memmap, if you destroy the namespace
and shrink the zone, it will initialize the memmap outside the zone and
trigger VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page) in
set_pfnblock_flags_mask()."

This BUG is also mitigated by this commit, where we for now stop to
shrink the ZONE_DEVICE zone until we can do it in a safe and clean
way.

--

Thanks,

David / dhildenb