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BL3PR12MB6644 On 14 Feb 2025, at 10:48, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: df5d6180169a Add linux-next specific files for 20250210= > git tree: linux-next > console+strace: https://syzkaller.appspot.com/x/log.txt?x=3D16d343f8580= 000 > kernel config: https://syzkaller.appspot.com/x/.config?x=3D2cd616b6e73= 6ca7 > dashboard link: https://syzkaller.appspot.com/bug?extid=3D012c6245eaea0= e23f7f9 > compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for D= ebian) 2.40 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=3D138972a45= 80000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=3D11737b18580= 000 > > Downloadable assets: > disk image: https://storage.googleapis.com/syzbot-assets/92495cf20271/d= isk-df5d6180.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/4b3656161842/vmli= nux-df5d6180.xz > kernel image: https://storage.googleapis.com/syzbot-assets/7fbc4e7a0f5d= /bzImage-df5d6180.xz > > The issue was bisected to: > > commit 19c067c8a0f18b62d4a4235b0b327624c86f2e40 > Author: Zi Yan > Date: Wed Feb 5 03:14:13 2025 +0000 > > mm/huge_memory: add buddy allocator like folio_split() > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=3D102f9bdf= 980000 > final oops: https://syzkaller.appspot.com/x/report.txt?x=3D122f9bdf= 980000 > console output: https://syzkaller.appspot.com/x/log.txt?x=3D142f9bdf980= 000 > > IMPORTANT: if you fix the issue, please add the following tag to the co= mmit: > Reported-by: syzbot+012c6245eaea0e23f7f9@syzkaller.appspotmail.com > Fixes: 19c067c8a0f1 ("mm/huge_memory: add buddy allocator like folio_sp= lit()") > > Oops: general protection fault, probably for non-canonical address 0xdf= fffc0000000024: 0000 [#1] PREEMPT SMP KASAN PTI > KASAN: null-ptr-deref in range [0x0000000000000120-0x0000000000000127] > CPU: 1 UID: 0 PID: 5949 Comm: syz-executor163 Not tainted 6.14.0-rc2-ne= xt-20250210-syzkaller #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS= Google 12/27/2024 > RIP: 0010:shmem_mapping+0x25/0x50 mm/shmem.c:281 > Code: 90 90 90 90 90 f3 0f 1e fa 53 48 89 fb e8 c3 3a bd ff 48 81 c3 20= 01 00 00 48 89 d8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df <80> 3c 08 0= 0 74 08 48 89 df e8 dd 35 24 00 48 c7 c0 80 6c 14 8c 48 > RSP: 0018:ffffc90004036dd8 EFLAGS: 00010006 > RAX: 0000000000000024 RBX: 0000000000000120 RCX: dffffc0000000000 > RDX: 0000000000000000 RSI: 0000000000000600 RDI: 0000000000000000 > RBP: 0000000000000600 R08: ffffffff822bcf18 R09: 1ffffd4000331008 > R10: dffffc0000000000 R11: fffff94000331009 R12: ffffea0001988018 > R13: ffffea0001988080 R14: ffffea0001988018 R15: ffffea0001988000 > FS: 00007f5e045316c0(0000) GS:ffff8880b8700000(0000) knlGS:00000000000= 00000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007f5e0458dae0 CR3: 0000000023c78000 CR4: 00000000003526f0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > Call Trace: > > __split_unmapped_folio+0x238a/0x3e50 mm/huge_memory.c:3587 > __folio_split+0x1267/0x16d0 mm/huge_memory.c:3871 > try_folio_split include/linux/huge_mm.h:374 [inline] > truncate_inode_partial_folio+0x55d/0xdc0 mm/truncate.c:230 > shmem_undo_range+0xab7/0x1820 mm/shmem.c:1144 > shmem_truncate_range mm/shmem.c:1224 [inline] > shmem_fallocate+0x431/0xf20 mm/shmem.c:3674 > vfs_fallocate+0x623/0x7a0 fs/open.c:338 > madvise_remove mm/madvise.c:1034 [inline] > madvise_vma_behavior mm/madvise.c:1269 [inline] > madvise_walk_vmas mm/madvise.c:1511 [inline] > madvise_do_behavior+0x1f29/0x3c00 mm/madvise.c:1646 > do_madvise mm/madvise.c:1744 [inline] > __do_sys_madvise mm/madvise.c:1752 [inline] > __se_sys_madvise mm/madvise.c:1750 [inline] > __x64_sys_madvise+0x11b/0x140 mm/madvise.c:1750 > do_syscall_x64 arch/x86/entry/common.c:52 [inline] > do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > RIP: 0033:0x7f5e04576519 > Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 51 18 00 00 90 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 f= 0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48 > RSP: 002b:00007f5e04531218 EFLAGS: 00000246 ORIG_RAX: 000000000000001c > RAX: ffffffffffffffda RBX: 00007f5e04600308 RCX: 00007f5e04576519 > RDX: 0000000000000009 RSI: 0000000000600003 RDI: 0000400000000000 > RBP: 00007f5e04600300 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000246 R12: 00007f5e045cd074 > R13: 0000400000000000 R14: 0000400000000140 R15: 0000400000000040 > > Modules linked in: > ---[ end trace 0000000000000000 ]--- > RIP: 0010:shmem_mapping+0x25/0x50 mm/shmem.c:281 > Code: 90 90 90 90 90 f3 0f 1e fa 53 48 89 fb e8 c3 3a bd ff 48 81 c3 20= 01 00 00 48 89 d8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df <80> 3c 08 0= 0 74 08 48 89 df e8 dd 35 24 00 48 c7 c0 80 6c 14 8c 48 > RSP: 0018:ffffc90004036dd8 EFLAGS: 00010006 > RAX: 0000000000000024 RBX: 0000000000000120 RCX: dffffc0000000000 > RDX: 0000000000000000 RSI: 0000000000000600 RDI: 0000000000000000 > RBP: 0000000000000600 R08: ffffffff822bcf18 R09: 1ffffd4000331008 > R10: dffffc0000000000 R11: fffff94000331009 R12: ffffea0001988018 > R13: ffffea0001988080 R14: ffffea0001988018 R15: ffffea0001988000 > FS: 00007f5e045316c0(0000) GS:ffff8880b8700000(0000) knlGS:00000000000= 00000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007f5e0458dae0 CR3: 0000000023c78000 CR4: 00000000003526f0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > ---------------- > Code disassembly (best guess): > 0: 90 nop > 1: 90 nop > 2: 90 nop > 3: 90 nop > 4: 90 nop > 5: f3 0f 1e fa endbr64 > 9: 53 push %rbx > a: 48 89 fb mov %rdi,%rbx > d: e8 c3 3a bd ff call 0xffbd3ad5 > 12: 48 81 c3 20 01 00 00 add $0x120,%rbx > 19: 48 89 d8 mov %rbx,%rax > 1c: 48 c1 e8 03 shr $0x3,%rax > 20: 48 b9 00 00 00 00 00 movabs $0xdffffc0000000000,%rcx > 27: fc ff df > * 2a: 80 3c 08 00 cmpb $0x0,(%rax,%rcx,1) <-- trapping inst= ruction > 2e: 74 08 je 0x38 > 30: 48 89 df mov %rbx,%rdi > 33: e8 dd 35 24 00 call 0x243615 > 38: 48 c7 c0 80 6c 14 8c mov $0xffffffff8c146c80,%rax > 3f: 48 rex.W > #syz test: github.com:x-y-z/linux-1gb-thp.git syzkaller_fix_20250114 origin_folio->mapping becomes NULL, since it was dropped, and the remaini= ng after-split folios are still trying to use origin_folio->mapping. It lead= s to the error. And the original __split_huge_page() did not check origin_folio->index nor dropped it. __split_unmapped_folio() should keep the original behavior. Fixed it by not dropping origin_folio. My local test do not fail and I am triggering syzbot to test the change to confirm it. Best Regards, Yan, Zi