On Wed, Jan 25, 2023 at 11:59:16PM +0000, Sanan Hasanov wrote: > Good day, dear maintainers, > > We found a bug using a modified kernel configuration file used by syzbot. > > We enhanced the coverage of the configuration file using our tool, klocalizer. > > Kernel Branch: 6.2.0-rc5-next-20230124 > Kernel config: https://drive.google.com/file/d/1MZSgIF4R9QfikEuF5siUIZVPce-GiJQK/view?usp=sharing > Reproducer: https://drive.google.com/file/d/1H5KWkT9VVMWTUVVgIaZi6J-fmukRx-BM/view?usp=sharing > > Thank you! > > Best regards, > Sanan Hasanov > > head: 0000000000020000 0000000000000000 00000004ffffffff ffff8881002b8000 > page dumped because: VM_BUG_ON_PAGE(!first && (flags & (( rmap_t)((((1UL))) << (0))))) > ------------[ cut here ]------------ I know it says "cut here" and you did that, but including just a few lines above that would be so much more helpful. I can infer that this is a multi-page folio, but more than that is hard to tell. > kernel BUG at mm/rmap.c:1248! That tracks with VM_BUG_ON_PAGE(!first && (flags & RMAP_EXCLUSIVE), page); > invalid opcode: 0000 [#1] PREEMPT SMP KASAN > CPU: 7 PID: 14932 Comm: syz-executor.1 Not tainted 6.2.0-rc5-next-20230124 #1 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 > RIP: 0010:page_add_anon_rmap+0xddd/0x11c0 mm/rmap.c:1248 > Code: c0 ff 48 8b 34 24 48 89 df e8 1f ff 07 00 49 89 c6 e9 85 f6 ff ff e8 52 73 c0 ff 48 c7 c6 c0 3c d8 89 48 89 ef e8 b3 23 f8 ff <0f> 0b e8 3c 73 c0 ff 48 c7 c6 00 3b d8 89 48 89 ef e8 9d 23 f8 ff > RSP: 0018:ffffc9000c56f7b0 EFLAGS: 00010293 > RAX: 0000000000000000 RBX: ffff88807efc6f30 RCX: 0000000000000000 > RDX: ffff8880464fd7c0 RSI: ffffffff81be733d RDI: fffff520018adedb > RBP: ffffea0000c68080 R08: 0000000000000056 R09: 0000000000000000 > R10: 0000000000000001 R11: 0000000000000001 R12: ffffea0000c68000 > R13: 0000000000000001 R14: ffffea0000c68088 R15: 0000000000000000 > FS: 00007f717898a700(0000) GS:ffff888119f80000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007f7178947d78 CR3: 000000004a9e6000 CR4: 0000000000350ee0 > Call Trace: > <TASK> > remove_migration_pte+0xaa6/0x1390 mm/migrate.c:261 if (folio_test_anon(folio)) page_add_anon_rmap(new, vma, pvmw.address, rmap_flags); Earlier in that function, we had: if (folio_test_anon(folio) && !is_readable_migration_entry(entry)) rmap_flags |= RMAP_EXCLUSIVE; so that also makes sense. We can also infer that RMAP_COMPOUND wasn't set, so we're trying to do just one page from the folio. All right, back to rmap.c: first = atomic_inc_and_test(&page->_mapcount); So first is clearly false (ie _mapcount was not -1), implying somebody else already mapped this page. Not really sure what's going on at this point. Seems unlikely that the folio changes in remove_migration_pte() are responsible since they're from last January. Huang has some more changes to migrate.c that I don't feel qualified to judge. Nothing's jumping out at me as obviously wrong. Is it possible to do a bisect? > rmap_walk_anon+0x23a/0x5b0 mm/rmap.c:2433 > rmap_walk+0x96/0xd0 mm/rmap.c:2509 > remove_migration_ptes mm/migrate.c:294 [inline] > migrate_folio_move mm/migrate.c:1307 [inline] > migrate_pages_batch+0x15f8/0x3910 mm/migrate.c:1809 > migrate_pages+0x1b56/0x22e0 mm/migrate.c:1961 > do_mbind mm/mempolicy.c:1329 [inline] > kernel_mbind+0x4c0/0x790 mm/mempolicy.c:1476 > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > do_syscall_64+0x39/0x80 arch/x86/entry/common.c:80 > entry_SYSCALL_64_after_hwframe+0x63/0xcd > RIP: 0033:0x7f717788edcd > Code: 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48 > RSP: 002b:00007f7178989bf8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ed > RAX: ffffffffffffffda RBX: 00007f71779bc050 RCX: 00007f717788edcd > RDX: 0000000000000004 RSI: 0000000000001000 RDI: 0000000020002000 > RBP: 00007f71778fc59c R08: 00000000000007ff R09: 0000000000000002 > R10: 00000000200000c0 R11: 0000000000000246 R12: 0000000000000000 > R13: 00007ffd2c012f6f R14: 00007ffd2c013110 R15: 00007f7178989d80 > </TASK> > Modules linked in: > ---[ end trace 0000000000000000 ]--- > RIP: 0010:page_add_anon_rmap+0xddd/0x11c0 mm/rmap.c:1248 > Code: c0 ff 48 8b 34 24 48 89 df e8 1f ff 07 00 49 89 c6 e9 85 f6 ff ff e8 52 73 c0 ff 48 c7 c6 c0 3c d8 89 48 89 ef e8 b3 23 f8 ff <0f> 0b e8 3c 73 c0 ff 48 c7 c6 00 3b d8 89 48 89 ef e8 9d 23 f8 ff > RSP: 0018:ffffc9000c56f7b0 EFLAGS: 00010293 > RAX: 0000000000000000 RBX: ffff88807efc6f30 RCX: 0000000000000000 > RDX: ffff8880464fd7c0 RSI: ffffffff81be733d RDI: fffff520018adedb > RBP: ffffea0000c68080 R08: 0000000000000056 R09: 0000000000000000 > R10: 0000000000000001 R11: 0000000000000001 R12: ffffea0000c68000 > R13: 0000000000000001 R14: ffffea0000c68088 R15: 0000000000000000 > FS: 00007f717898a700(0000) GS:ffff888119f80000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007f7178947d78 CR3: 000000004a9e6000 CR4: 0000000000350ee0 >
