Hi Friends, I may have hit on a possible bug with remove_pagetables. However, so far, I have only been able to reproduce it with my out-of-tree p2pmem patchset (so I understand if you don't consider it a bug). At this time, I have not able been able to reproduce it using device-dax. Starting with v4.12-rc1 and including rc3, if I insert PCI bar memory using devm_memremap_pages, then remove it, then insert it again I hit a kernel BUG (see below). I did a quick bisect to find the commit that causes this is: e6ab9c4d4: x86/mm/64: Fix crash in remove_pagetable() If I print the output of pgd_page_vaddr and p4d_offset, I get very different addresses: pgd_page_vaddr: ffff88026c04d000 p4d_offset: ffffffff81e0aea8 The version of p4d_offset my kernel is using is the one in pgtable-nop4d.h which simply returns a casted version of pgd. This seems slightly suspect but I can't say I understand this code all that well. Thanks for your help, Logan > [ 111.501162] ------------[ cut here ]------------ > [ 111.506427] kernel BUG at arch/x86/mm/init_64.c:128! > [ 111.512080] invalid opcode: 0000 [#1] SMP > [ 111.516662] Modules linked in: mtr_p2pmem(O+) [last unloaded: mtr_p2pmem] > [ 111.524357] CPU: 4 PID: 2317 Comm: insmod Tainted: G O 4.11.0-rc5.direct-00148-g052a6536f8db #435 > [ 111.535667] Hardware name: Supermicro SYS-7047GR-TRF/X9DRG-QF, BIOS 3.0a 12/05/2013 > [ 111.544352] task: ffff880274d54300 task.stack: ffffc90002edc000 > [ 111.551079] RIP: 0010:sync_global_pgds+0x134/0x140 > [ 111.556535] RSP: 0018:ffffc90002edfaa8 EFLAGS: 00010287 > [ 111.562477] RAX: 00003ffffffff000 RBX: 0000000000000c00 RCX: ffffc08000000000 > [ 111.570556] RDX: 0000000000000001 RSI: ffff88046d462000 RDI: ffff8802749ed000 > [ 111.578628] RBP: ffff880000000000 R08: ffffffff81e0ac00 R09: 000000046d462067 > [ 111.586710] R10: ffff88046d462000 R11: ffff880474bdd1e0 R12: ffffffff81e0ac00 > [ 111.594789] R13: ffff8804775f3c00 R14: ffff8804775c1400 R15: ffffea0011dd7cc0 > [ 111.602871] FS: 00007f3f39999700(0000) GS:ffff88047fc00000(0000) knlGS:0000000000000000 > [ 111.612043] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 111.618569] CR2: 000055e04c19f1d8 CR3: 00000004771f0000 CR4: 00000000000406e0 > [ 111.626651] Call Trace: > [ 111.629491] ? kernel_physical_mapping_init+0x1c2/0x1e2 > [ 111.635438] ? init_memory_mapping+0x1c0/0x370 > [ 111.640509] ? walk_system_ram_range+0x6d/0xb0 > [ 111.645578] ? arch_add_memory+0x4b/0xe0 > [ 111.650067] ? devm_memremap_pages+0x276/0x3c0 > [ 111.655141] ? p2pmem_add_resource+0x25/0xc0 > [ 111.660016] ? mtramon_init+0x17a/0x1000 [mtr_p2pmem] > [ 111.665764] ? 0xffffffffa000a000 > [ 111.669570] ? do_one_initcall+0x39/0x170 > [ 111.674154] ? do_init_module+0x55/0x1e5 > [ 111.678643] ? load_module+0x24ae/0x29a0 > [ 111.683130] ? SYSC_finit_module+0x91/0xc0 > [ 111.687811] ? SYSC_finit_module+0x91/0xc0 > [ 111.692492] ? entry_SYSCALL_64_fastpath+0x13/0x94 > [ 111.697950] Code: 49 f7 45 00 9f ff ff ff 75 a3 49 89 75 00 eb 9d c6 05 a8 85 00 01 00 e9 06 ff ff ff 48 83 c4 10 5b 5d 41 5c 41 5d 41 5e 41 5f c3 <0f> 0b 66 2e 0f 1f 84 00 00 00 00 00 55 53 48 89 f3 48 89 d5 e8 > [ 111.719213] RIP: sync_global_pgds+0x134/0x140 RSP: ffffc90002edfaa8 > [ 111.726340] ---[ end trace 34982079c1a73cd0 ]--- -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
