Re: [PATCH v3 23/29] arch, mm: consolidate initialization of nodes, zones and memory map

[Vlastimil Babka <vbabka@suse.cz>]

On 1/11/26 09:20, Mike Rapoport wrote:
> From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
> 
> To initialize node, zone and memory map data structures every architecture
> calls free_area_init() during setup_arch() and passes it an array of zone
> limits.
> 
> Beside code duplication it creates "interesting" ordering cases between
> allocation and initialization of hugetlb and the memory map. Some
> architectures allocate hugetlb pages very early in setup_arch() in certain
> cases, some only create hugetlb CMA areas in setup_arch() and sometimes
> hugetlb allocations happen mm_core_init().
> 
> With arch_zone_limits_init() helper available now on all architectures it
> is no longer necessary to call free_area_init() from architecture setup
> code. Rather core MM initialization can call arch_zone_limits_init() in a
> single place.
> 
> This allows to unify ordering of hugetlb vs memory map allocation and
> initialization.
> 
> Remove the call to free_area_init() from architecture specific code and
> place it in a new mm_core_init_early() function that is called immediately
> after setup_arch().
> 
> After this refactoring it is possible to consolidate hugetlb allocations
> and eliminate differences in ordering of hugetlb and memory map
> initialization among different architectures.
> 
> As the first step of this consolidation move hugetlb_bootmem_alloc() to
> mm_core_early_init().
> 
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
I've bisected a problem with virtme-ng testing a NUMA memoryless
node setup (on x86_64) to this patch (commit d49004c5f0c1).

It's executed like this, where node 0 has memory and node 1 only cpus:

vng -vr . -p 8 -m 4G --numa 4G,cpus=0-3 --numa 0,cpus=4-7

This fails to boot due to:

[    0.095894] BUG: unable to handle page fault for address: 0000000000004620
[    0.097196] #PF: supervisor read access in kernel mode
[    0.098180] #PF: error_code(0x0000) - not-present page
[    0.099155] PGD 0 P4D 0 
[    0.099641] Oops: Oops: 0000 [#1] SMP NOPTI
[    0.100437] CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 6.19.0-rc6-00152-gf206359553c9 #53 PREEMPT 
[    0.102201] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.17.0-2-g4f253b9b-prebuilt.qemu.org 04/01/2014
[    0.104313] RIP: 0010:mm_core_init_early+0x263/0x900
[    0.105271] Code: 93 ff 72 09 8b 7c 24 30 e8 da 82 00 00 48 63 44 24 30 45 31 db 4c 8b 24 c5 a0 7b 1d 9a 48 89 c3 4c 89 5c 24 50 4c 89 5c 24 58 <41> 83 bc 24 20 46 00 00 00 75 0b 41 83 bc 24 14 47 00 00 00 74 04
[    0.108863] RSP: 0000:ffffffff99403e38 EFLAGS: 00010046
[    0.109861] RAX: 0000000000000001 RBX: 0000000000000001 RCX: 0000000000000001
[    0.111223] RDX: 0000000000000040 RSI: 0000000000100000 RDI: ffff89597fffae00
[    0.112577] RBP: 0000000000000005 R08: 0000000000000000 R09: ffff89597fffa200
[    0.113924] R10: 80000000ffffe000 R11: 0000000000000000 R12: 0000000000000000
[    0.115294] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[    0.116656] FS:  0000000000000000(0000) GS:0000000000000000(0000) knlGS:0000000000000000
[    0.118193] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    0.119283] CR2: 0000000000004620 CR3: 0000000060048000 CR4: 00000000000000b0
[    0.120645] Call Trace:
[    0.121122]  <TASK>
[    0.121521]  start_kernel+0x5d/0x780
[    0.122206]  x86_64_start_reservations+0x24/0x30
[    0.123079]  x86_64_start_kernel+0xd1/0xe0
[    0.123860]  common_startup_64+0x12c/0x138
[    0.124641]  </TASK>
[    0.125061] Modules linked in:
[    0.125646] CR2: 0000000000004620
[    0.126279] ---[ end trace 0000000000000000 ]---
[    0.127162] RIP: 0010:mm_core_init_early+0x263/0x900
[    0.128106] Code: 93 ff 72 09 8b 7c 24 30 e8 da 82 00 00 48 63 44 24 30 45 31 db 4c 8b 24 c5 a0 7b 1d 9a 48 89 c3 4c 89 5c 24 50 4c 89 5c 24 58 <41> 83 bc 24 20 46 00 00 00 75 0b 41 83 bc 24 14 47 00 00 00 74 04
[    0.131676] RSP: 0000:ffffffff99403e38 EFLAGS: 00010046
[    0.132684] RAX: 0000000000000001 RBX: 0000000000000001 RCX: 0000000000000001
[    0.134033] RDX: 0000000000000040 RSI: 0000000000100000 RDI: ffff89597fffae00
[    0.135412] RBP: 0000000000000005 R08: 0000000000000000 R09: ffff89597fffa200
[    0.136763] R10: 80000000ffffe000 R11: 0000000000000000 R12: 0000000000000000
[    0.138112] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[    0.139487] FS:  0000000000000000(0000) GS:0000000000000000(0000) knlGS:0000000000000000
[    0.141014] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    0.142094] CR2: 0000000000004620 CR3: 0000000060048000 CR4: 00000000000000b0
[    0.143448] Kernel panic - not syncing: Attempted to kill the idle task!
[    0.144833] ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---

> ./scripts/faddr2line vmlinux mm_core_init_early+0x263/0x900
mm_core_init_early+0x263/0x900:
free_area_init_node at mm/mm_init.c:1721
(inlined by) free_area_init at mm/mm_init.c:1902
(inlined by) mm_core_init_early at mm/mm_init.c:2681

It crashes at WARN_ON(pgdat->nr_zones || pgdat->kswapd_highest_zoneidx);
because pgdat is NULL.

With some debug printk's I've figured out that in free_area_init()
we have:

                if (!node_online(nid))
                        alloc_offline_node_data(nid);
             
                pgdat = NODE_DATA(nid);
                free_area_init_node(nid);


But node_online() is true so this allocation doesn't happen, and
pgdat remains NULL.

And node_online() becomes true in init_cpu_to_node():

                if (!node_online(node))
                        node_set_online(node);

But without having a pgdat allocated.

I was able to workaround this by changing the code in free_area_init() to

               if (!node_online(nid) || !NODE_DATA(nid))
                        alloc_offline_node_data(nid);

But I don't have the bigger picture, and also didn't check yet what exactly
about this patch results in the failure. Probably ordering of various related 
actions. Thoughts?