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Wed, 14 Oct 2026 08:36:06 -0700 (PDT) From: Ritesh Harjani (IBM) To: Muchun Song , Madhavan Srinivasan , Mike Rapoport , Andrew Morton , David Hildenbrand Cc: Michael Ellerman , Nicholas Piggin , Christophe Leroy , Shrikanth Hegde , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Qi Zheng , Lance Yang , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Muchun Song , muchun.song@linux.dev Subject: Re: [PATCH v4 0/6] mm: Unify device DAX and HugeTLB vmemmap population paths In-Reply-To: <20261010075755.83339-1-songmuchun@bytedance.com> Date: Wed, 14 Oct 2026 20:19:23 +0530 Message-ID: References: <20261010075755.83339-1-songmuchun@bytedance.com> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list Muchun Song writes: > This v4 is based on mm-new commit d5207c6d152c, which contains v6 of > "mm: Switch device DAX to section-based vmemmap optimization" [1]. > Hi Muchun, I was checking this patch series and seems like I am hitting an issue on mm-new, which most likely is due to this patch series. (Note that a similar issue was reported by Pavithra on PowerPC) Let me first give the call stack: [ 79.930815] page: refcount:0 mapcount:1 mapping:0000000000000000 index:0x0 pfn:0x140000 [ 79.930833] flags: 0x0(node=0|zone=0|lastcpupid=0x0) [ 79.930838] raw: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 [ 79.930840] raw: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 [ 79.930841] page dumped because: VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn)) [ 79.931043] ------------[ cut here ]------------ [ 79.931051] kernel BUG at mm/page_alloc.c:373! [ 79.931109] Oops: invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC PTI [ 79.940576] CPU: 2 UID: 0 PID: 743 Comm: ndctl Tainted: G N 7.3.0-rc5-01065-g45f4c1453cbe #23 PREEMPT(full) [ 79.942647] Tainted: [N]=TEST [ 79.943190] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 [ 79.945080] RIP: 0010:__set_pfnblock_flags_mask.constprop.0+0xef/0x110 [ 79.946231] Code: 48 8b 07 48 89 d1 48 f7 d1 48 89 c2 48 21 ca 48 09 f2 f0 48 0f b1 17 75 f0 c3 cc cc cc cc 48 c7 c6 b0 9b 5a 83 e8 91 be fa ff <0f> 0b ba 00 10 00 00 e9 7a ff ff ff 48 c7 c6 a8 b5 56 83 e8 79 be [ 79.949296] RSP: 0018:ffffc90011ebf7b0 EFLAGS: 00010246 [ 79.950179] RAX: 000000000000004a RBX: 0000000000140000 RCX: 0000000000000000 [ 79.951366] RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffffffffffff [ 79.952562] RBP: 0000000000180000 R08: 0000000000000001 R09: 0000000000000000 [ 79.953759] R10: 0000000000000118 R11: 0000000000008000 R12: 0000000000000001 [ 79.954948] R13: 0000000000000000 R14: 0000000000180000 R15: 0000000000190000 [ 79.956151] FS: 00007ffff7e36d40(0000) GS:ffff8880f7f22000(0000) knlGS:0000000000000000 [ 79.957490] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 79.958464] CR2: 000055555572ce90 CR3: 0000000031130003 CR4: 0000000000172ef0 [ 79.959657] Call Trace: [ 79.960096] [ 79.960487] pageblock_migratetype_init_range.constprop.0+0x50/0x90 [ 79.961561] memmap_init_zone_device+0x2fb/0x380 [ 79.962392] pagemap_range+0x272/0x590 [ 79.963069] memremap_pages+0x125/0x210 [ 79.963726] ? lockdep_hardirqs_on+0x7d/0x100 [ 79.964488] devm_memremap_pages+0x21/0x70 [ 79.965191] dev_dax_probe+0x1db/0x300 [ 79.965870] dax_bus_probe+0x6f/0xa0 [ 79.966495] call_driver_probe+0x24/0xf0 [ 79.967190] really_probe+0xb6/0x310 [ 79.967810] ? __pfx___device_attach_driver+0x10/0x10 [ 79.968667] __driver_probe_device+0x87/0x190 [ 79.969415] ? __pfx___device_attach_driver+0x10/0x10 [ 79.970270] driver_probe_device+0x1f/0x90 [ 79.970976] __device_attach_driver+0x89/0x130 [ 79.971734] bus_for_each_drv+0x86/0xe0 [ 79.972412] __device_attach+0xb6/0x1d0 [ 79.973078] device_initial_probe+0x40/0x60 [ 79.973791] bus_probe_device+0x3d/0xa0 [ 79.974453] device_add+0x4f0/0x6c0 [ 79.975068] __devm_create_dev_dax+0x18b/0x3f0 [ 79.975830] devm_create_dev_dax+0x21/0x40 [ 79.976530] __dax_pmem_probe+0x1c3/0x200 [ 79.977244] dax_pmem_probe+0xe/0x20 [ 79.977867] nvdimm_bus_probe+0x89/0x250 [ 79.978566] call_driver_probe+0x24/0xf0 [ 79.979242] really_probe+0xb6/0x310 [ 79.979868] __driver_probe_device+0x87/0x190 [ 79.980618] device_driver_attach+0x47/0xb0 [ 79.981336] bind_store+0x76/0xc0 [ 79.981922] kernfs_fop_write_iter+0x152/0x200 [ 79.982715] vfs_write+0x276/0x520 [ 79.983323] ksys_write+0x6b/0xe0 [ 79.983900] do_syscall_64+0xa6/0x470 [ 79.984543] entry_SYSCALL_64_after_hwframe+0x76/0x7e also - [ 4.426995] BUG: kernel NULL pointer dereference, address: 0000000000000090 [ 4.428266] #PF: supervisor read access in kernel mode [ 4.428266] #PF: error_code(0x0000) - not-present page [ 4.428266] PGD 0 P4D 0 [ 4.428266] Oops: Oops: 0000 [#1] SMP DEBUG_PAGEALLOC PTI [ 4.428266] CPU: 6 UID: 0 PID: 1 Comm: swapper/0 Not tainted 7.3.0-rc5-01065-g45f4c1453c [ 4.428266] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f04 [ 4.428266] RIP: 0010:__set_pfnblock_flags_mask.constprop.0+0x3d/0x110 [ 4.428266] Code: 84 e3 00 00 00 48 8b 17 48 89 d1 48 c1 ea 37 83 e2 07 48 c1 e9 3a 48 8d 14 52 40 [ 4.428266] RSP: 0000:ffffc9000001b770 EFLAGS: 00010246 [ 4.428266] RAX: 0000000000140000 RBX: 0000000000140000 RCX: 0000000000000020 [ 4.428266] RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffea0005000000 [ 4.428266] RBP: 0000000000180000 R08: ffff8880093e1600 R09: 0000000000000040 [ 4.428266] R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000001 [ 4.428266] R13: 0000000000000000 R14: 0000000000180000 R15: 0000000000190000 [ 4.428266] FS: 0000000000000000(0000) GS:ffff8880f8722000(0000) knlGS:0000000000000000 [ 4.428266] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 4.428266] CR2: 0000000000000090 CR3: 0000000003aac001 CR4: 0000000000172ef0 [ 4.428266] Call Trace: [ 4.428266] [ 4.428266] pageblock_migratetype_init_range.constprop.0+0x50/0x90 [ 4.428266] memmap_init_zone_device+0x2fb/0x380 [ 4.428266] pagemap_range+0x272/0x590 [ 4.428266] memremap_pages+0x125/0x210 [ 4.428266] ? lockdep_hardirqs_on+0x7d/0x100 [ 4.428266] devm_memremap_pages+0x21/0x70 [ 4.428266] dev_dax_probe+0x1db/0x300 [ 4.428266] dax_bus_probe+0x6f/0xa0 [ 4.428266] call_driver_probe+0x24/0xf0 [ 4.428266] really_probe+0xb6/0x310 [ 4.428266] ? __pfx___device_attach_driver+0x10/0x10 [ 4.428266] __driver_probe_device+0x87/0x190 [ 4.428266] ? __pfx___device_attach_driver+0x10/0x10 [ 4.428266] driver_probe_device+0x1f/0x90 [ 4.428266] __device_attach_driver+0x89/0x130 [ 4.428266] bus_for_each_drv+0x86/0xe0 [ 4.428266] __device_attach+0xb6/0x1d0 [ 4.428266] device_initial_probe+0x40/0x60 [ 4.428266] bus_probe_device+0x3d/0xa0 [ 4.428266] device_add+0x4f0/0x6c0 [ 4.428266] __devm_create_dev_dax+0x18b/0x3f0 [ 4.428266] devm_create_dev_dax+0x21/0x40 [ 4.428266] __dax_pmem_probe+0x1c3/0x200 [ 4.428266] dax_pmem_probe+0xe/0x20 [ 4.428266] nvdimm_bus_probe+0x89/0x250 [ 4.428266] call_driver_probe+0x24/0xf0 [ 4.428266] really_probe+0xb6/0x310 [ 4.428266] ? __pfx___driver_attach+0x10/0x10 [ 4.428266] __driver_probe_device+0x87/0x190 [ 4.428266] ? __pfx___driver_attach+0x10/0x10 [ 4.428266] driver_probe_device+0x1f/0x90 [ 4.428266] __driver_attach+0xd7/0x200 [ 4.428266] bus_for_each_dev+0x79/0xc0 [ 4.428266] bus_add_driver+0x127/0x250 [ 4.428266] driver_register+0x59/0x100 [ 4.428266] ? __pfx_dax_pmem_init+0x10/0x10 [ 4.428266] do_one_initcall+0x59/0x3a0 [ 4.428266] do_initcalls+0xdd/0x1b0 [ 4.428266] kernel_init_freeable+0x16f/0x2b0 [ 4.428266] ? __pfx_kernel_init+0x10/0x10 [ 4.428266] kernel_init+0x1f/0x1d0 [ 4.428266] ret_from_fork+0x244/0x280 [ 4.428266] ? __pfx_kernel_init+0x10/0x10 [ 4.428266] ret_from_fork_asm+0x1a/0x30 [ 4.428266] - I am hitting this issue on x86 kvm itself (and also on PowerPC) - I am able to hit the issue with the following extra qemu params: -m 2G,slots=4,maxmem=16G -object memory-backend-file,id=mem1,mem-path=/tmp/nvdimm.img,size=2560M,share=on -device nvdimm,id=nvdimm0,memdev=mem1,label-size=256M,addr=0x100000000 # then once the system comes up ndctl disable-region region0 ndctl init-labels all ndctl enable-region region0 ndctl create-namespace -r region0 -t pmem -m raw -s 256M ndctl create-namespace -r region0 -t pmem -m devdax -M mem -a 1G -s 2G I am still debugging this issue - but from the logs it looks like that some struct page was never initialized which caused the VM_BUG_ON(). Can you take a look at this once? Thanks! -ritesh