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

[Andrew Morton]

On Tue, 19 Nov 2019 15:16:22 +0100 David Hildenbrand <david@xxxxxxxxxx> wrote:

> On 14.10.19 21:17, Andrew Morton wrote:
> > On Mon, 14 Oct 2019 11:32:13 +0200 David Hildenbrand <david@xxxxxxxxxx> 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@xxxxxxxxxxxxxxx # 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.
> 

OK, thanks.  I updated the changelog, added Reported-by:Toshiki and
shall squeeze this fix into 5.4.