====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ syz.4.15809/22188 is trying to acquire lock: ffffffff8ee90400 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:316 [inline] ffffffff8ee90400 (fs_reclaim){+.+.}-{0:0}, at: prepare_alloc_pages+0x149/0x600 mm/page_alloc.c:5113 but task is already holding lock: ffff8880296ea800 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_trylock include/linux/mmap_lock.h:619 [inline] ffff8880296ea800 (&mm->mmap_lock){++++}-{4:4}, at: get_mmap_lock_carefully mm/mmap_lock.c:441 [inline] ffff8880296ea800 (&mm->mmap_lock){++++}-{4:4}, at: lock_mm_and_find_vma+0x36/0x340 mm/mmap_lock.c:501 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #7 (&mm->mmap_lock){++++}-{4:4}: __might_fault+0xcb/0x130 mm/memory.c:7482 _copy_from_iter+0x100/0x1660 lib/iov_iter.c:271 copy_from_iter include/linux/uio.h:228 [inline] copy_from_iter_full include/linux/uio.h:245 [inline] skb_do_copy_data_nocache include/net/sock.h:2329 [inline] skb_copy_to_page_nocache include/net/sock.h:2355 [inline] tcp_sendmsg_locked+0x20cf/0x5400 net/ipv4/tcp.c:1310 tcp_sendmsg+0x2f/0x50 net/ipv4/tcp.c:1451 sock_sendmsg_nosec+0x10e/0x180 net/socket.c:801 __sock_sendmsg net/socket.c:815 [inline] sock_write_iter+0x2de/0x3e0 net/socket.c:1266 new_sync_write fs/read_write.c:595 [inline] vfs_write+0x612/0xba0 fs/read_write.c:687 ksys_write+0x150/0x270 fs/read_write.c:739 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #6 (sk_lock-AF_INET){+.+.}-{0:0}: lock_sock_nested+0x41/0x100 net/core/sock.c:3837 lock_sock include/net/sock.h:1713 [inline] inet_shutdown+0x6a/0x390 net/ipv4/af_inet.c:913 nbd_mark_nsock_dead+0x2cb/0x550 drivers/block/nbd.c:319 recv_work+0x1cee/0x1e10 drivers/block/nbd.c:1030 process_one_work kernel/workqueue.c:3396 [inline] process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3479 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3560 kthread+0x38b/0x480 kernel/kthread.c:436 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #5 (&nsock->tx_lock){+.+.}-{4:4}: __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821 nbd_handle_cmd drivers/block/nbd.c:1143 [inline] nbd_queue_rq+0x373/0xff0 drivers/block/nbd.c:1207 blk_mq_dispatch_rq_list+0x499/0x1990 block/blk-mq.c:2117 __blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline] blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline] __blk_mq_sched_dispatch_requests+0xd36/0x1580 block/blk-mq-sched.c:307 blk_mq_sched_dispatch_requests+0xd7/0x190 block/blk-mq-sched.c:329 blk_mq_run_work_fn+0x16c/0x300 block/blk-mq.c:2532 process_one_work kernel/workqueue.c:3396 [inline] process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3479 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3560 kthread+0x38b/0x480 kernel/kthread.c:436 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #4 (&cmd->lock){+.+.}-{4:4}: __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821 nbd_queue_rq+0xc1/0xff0 drivers/block/nbd.c:1199 blk_mq_dispatch_rq_list+0x499/0x1990 block/blk-mq.c:2117 __blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline] blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline] __blk_mq_sched_dispatch_requests+0xd36/0x1580 block/blk-mq-sched.c:307 blk_mq_sched_dispatch_requests+0xd7/0x190 block/blk-mq-sched.c:329 blk_mq_run_work_fn+0x16c/0x300 block/blk-mq.c:2532 process_one_work kernel/workqueue.c:3396 [inline] process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3479 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3560 kthread+0x38b/0x480 kernel/kthread.c:436 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #3 (set->srcu){.+.+}-{0:0}: srcu_lock_sync include/linux/srcu.h:210 [inline] __synchronize_srcu+0xc9/0x2f0 kernel/rcu/srcutree.c:1462 elevator_switch+0x1e8/0x7b0 block/elevator.c:576 elevator_change+0x2fa/0x480 block/elevator.c:681 elevator_set_default+0x375/0x440 block/elevator.c:754 blk_register_queue+0x3f3/0x4e0 block/blk-sysfs.c:992 __add_disk+0x6b8/0xdb0 block/genhd.c:531 add_disk_fwnode+0x100/0x3a0 block/genhd.c:600 add_disk include/linux/blkdev.h:798 [inline] nbd_dev_add+0x733/0xb60 drivers/block/nbd.c:2026 nbd_init+0x168/0x1f0 drivers/block/nbd.c:2743 do_one_initcall+0x250/0x870 init/main.c:1362 do_initcall_level+0x10a/0x1a0 init/main.c:1424 do_initcalls+0x59/0xa0 init/main.c:1440 kernel_init_freeable+0x29d/0x3e0 init/main.c:1675 kernel_init+0x22/0x1d0 init/main.c:1565 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #2 (&q->elevator_lock){+.+.}-{4:4}: __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821 elevator_change+0x1af/0x480 block/elevator.c:679 elevator_set_none+0xb5/0x140 block/elevator.c:769 blk_mq_elv_switch_none block/blk-mq.c:5102 [inline] __blk_mq_update_nr_hw_queues block/blk-mq.c:5147 [inline] blk_mq_update_nr_hw_queues+0x5ef/0x19f0 block/blk-mq.c:5212 nbd_start_device+0x189/0xb30 drivers/block/nbd.c:1530 nbd_genl_connect+0x167d/0x1cd0 drivers/block/nbd.c:2310 genl_family_rcv_msg_doit+0x233/0x340 net/netlink/genetlink.c:1114 genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline] genl_rcv_msg+0x614/0x7a0 net/netlink/genetlink.c:1209 netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2575 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218 netlink_unicast_kernel net/netlink/af_netlink.c:1338 [inline] netlink_unicast+0x7bd/0x940 net/netlink/af_netlink.c:1364 netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1919 sock_sendmsg_nosec+0x13a/0x180 net/socket.c:800 __sock_sendmsg net/socket.c:815 [inline] ____sys_sendmsg+0x54e/0x850 net/socket.c:2713 ___sys_sendmsg+0x2a5/0x360 net/socket.c:2767 __sys_sendmsg net/socket.c:2799 [inline] __do_sys_sendmsg net/socket.c:2804 [inline] __se_sys_sendmsg net/socket.c:2802 [inline] __x64_sys_sendmsg+0x1b1/0x290 net/socket.c:2802 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #1 (&q->q_usage_counter(io)#49){++++}-{0:0}: blk_alloc_queue+0x544/0x690 block/blk-core.c:504 blk_mq_alloc_queue block/blk-mq.c:4420 [inline] __blk_mq_alloc_disk+0x194/0x390 block/blk-mq.c:4467 nbd_dev_add+0x494/0xb60 drivers/block/nbd.c:1996 nbd_init+0x168/0x1f0 drivers/block/nbd.c:2743 do_one_initcall+0x250/0x870 init/main.c:1362 do_initcall_level+0x10a/0x1a0 init/main.c:1424 do_initcalls+0x59/0xa0 init/main.c:1440 kernel_init_freeable+0x29d/0x3e0 init/main.c:1675 kernel_init+0x22/0x1d0 init/main.c:1565 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #0 (fs_reclaim){+.+.}-{0:0}: check_prev_add kernel/locking/lockdep.c:3209 [inline] check_prevs_add kernel/locking/lockdep.c:3328 [inline] validate_chain kernel/locking/lockdep.c:3952 [inline] __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942 __fs_reclaim_acquire mm/page_alloc.c:4375 [inline] fs_reclaim_acquire+0x71/0x100 mm/page_alloc.c:4389 might_alloc include/linux/sched/mm.h:316 [inline] prepare_alloc_pages+0x149/0x600 mm/page_alloc.c:5113 __alloc_frozen_pages_noprof+0x185/0x5a0 mm/page_alloc.c:5421 alloc_pages_mpol+0x21e/0x390 mm/mempolicy.c:2486 alloc_frozen_pages_noprof mm/mempolicy.c:2557 [inline] alloc_pages_noprof+0xb1/0x2b0 mm/mempolicy.c:2577 pagetable_alloc_noprof include/linux/mm.h:3794 [inline] __pte_alloc_one_noprof include/asm-generic/pgalloc.h:76 [inline] pte_alloc_one+0x22/0x370 arch/x86/mm/pgtable.c:18 __do_fault+0xd1/0x2a0 mm/memory.c:5560 do_shared_fault mm/memory.c:6064 [inline] do_fault mm/memory.c:6138 [inline] do_pte_missing+0x684/0x34b0 mm/memory.c:4700 handle_pte_fault mm/memory.c:6558 [inline] __handle_mm_fault mm/memory.c:6707 [inline] handle_mm_fault+0x1a53/0x3750 mm/memory.c:6876 do_user_addr_fault+0x746/0x1340 arch/x86/mm/fault.c:1394 handle_page_fault arch/x86/mm/fault.c:1483 [inline] exc_page_fault+0x6a/0xc0 arch/x86/mm/fault.c:1536 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:595 __put_user_4+0xd/0x30 arch/x86/lib/putuser.S:92 pppox_ioctl+0x1de/0x3f0 drivers/net/ppp/pppox.c:86 sock_do_ioctl+0x101/0x320 net/socket.c:1325 sock_ioctl+0x57a/0x7e0 net/socket.c:1446 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:597 [inline] __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f other info that might help us debug this: Chain exists of: fs_reclaim --> sk_lock-AF_INET --> &mm->mmap_lock Possible unsafe locking scenario: CPU0 CPU1 ---- ---- rlock(&mm->mmap_lock); lock(sk_lock-AF_INET); lock(&mm->mmap_lock); lock(fs_reclaim); *** DEADLOCK *** locks held by syz.4.15809/22188: 2, last CPU#1: #0: ffff88805406a260 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1713 [inline] #0: ffff88805406a260 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: pppox_ioctl+0x4d/0x3f0 drivers/net/ppp/pppox.c:73 #1: ffff8880296ea800 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_trylock include/linux/mmap_lock.h:619 [inline] #1: ffff8880296ea800 (&mm->mmap_lock){++++}-{4:4}, at: get_mmap_lock_carefully mm/mmap_lock.c:441 [inline] #1: ffff8880296ea800 (&mm->mmap_lock){++++}-{4:4}, at: lock_mm_and_find_vma+0x36/0x340 mm/mmap_lock.c:501 stack backtrace: CPU: 1 UID: 0 PID: 22188 Comm: syz.4.15809 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026 Call Trace: dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120 print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2087 check_noncircular+0x12f/0x150 kernel/locking/lockdep.c:2219 check_prev_add kernel/locking/lockdep.c:3209 [inline] check_prevs_add kernel/locking/lockdep.c:3328 [inline] validate_chain kernel/locking/lockdep.c:3952 [inline] __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942 __fs_reclaim_acquire mm/page_alloc.c:4375 [inline] fs_reclaim_acquire+0x71/0x100 mm/page_alloc.c:4389 might_alloc include/linux/sched/mm.h:316 [inline] prepare_alloc_pages+0x149/0x600 mm/page_alloc.c:5113 __alloc_frozen_pages_noprof+0x185/0x5a0 mm/page_alloc.c:5421 alloc_pages_mpol+0x21e/0x390 mm/mempolicy.c:2486 alloc_frozen_pages_noprof mm/mempolicy.c:2557 [inline] alloc_pages_noprof+0xb1/0x2b0 mm/mempolicy.c:2577 pagetable_alloc_noprof include/linux/mm.h:3794 [inline] __pte_alloc_one_noprof include/asm-generic/pgalloc.h:76 [inline] pte_alloc_one+0x22/0x370 arch/x86/mm/pgtable.c:18 __do_fault+0xd1/0x2a0 mm/memory.c:5560 do_shared_fault mm/memory.c:6064 [inline] do_fault mm/memory.c:6138 [inline] do_pte_missing+0x684/0x34b0 mm/memory.c:4700 handle_pte_fault mm/memory.c:6558 [inline] __handle_mm_fault mm/memory.c:6707 [inline] handle_mm_fault+0x1a53/0x3750 mm/memory.c:6876 do_user_addr_fault+0x746/0x1340 arch/x86/mm/fault.c:1394 handle_page_fault arch/x86/mm/fault.c:1483 [inline] exc_page_fault+0x6a/0xc0 arch/x86/mm/fault.c:1536 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:595 RIP: 0010:__put_user_4+0xd/0x30 arch/x86/lib/putuser.S:94 Code: 66 89 01 31 c9 0f 01 ca c3 cc cc cc cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 48 89 cb 48 c1 fb 3f 48 09 d9 0f 01 cb <89> 01 31 c9 0f 01 ca e9 87 96 03 00 90 90 90 90 90 90 90 90 90 90 RSP: 0018:ffffc90006f7fc78 EFLAGS: 00050206 RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000200000000100 RDX: 00000000b1d1b595 RSI: ffffffff8e69f6ed RDI: ffffffff8c6dad80 RBP: 0000000000000001 R08: ffffffff821ed4ef R09: 0000000000000000 R10: dffffc0000000000 R11: fffffbfff20f4c90 R12: 0000200000000100 R13: 1ffff1100a80d402 R14: ffff88805406a000 R15: dffffc0000000000 pppox_ioctl+0x1de/0x3f0 drivers/net/ppp/pppox.c:86 sock_do_ioctl+0x101/0x320 net/socket.c:1325 sock_ioctl+0x57a/0x7e0 net/socket.c:1446 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:597 [inline] __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f6e7959e199 Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 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 e8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f6e777f6028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 00007f6e79825fa0 RCX: 00007f6e7959e199 RDX: 0000200000000100 RSI: 0000000080047437 RDI: 0000000000000004 RBP: 00007f6e796358e0 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f6e79826038 R14: 00007f6e79825fa0 R15: 00007fff580d0198 ---------------- Code disassembly (best guess): 0: 66 89 01 mov %ax,(%rcx) 3: 31 c9 xor %ecx,%ecx 5: 0f 01 ca clac 8: c3 ret 9: cc int3 a: cc int3 b: cc int3 c: cc int3 d: 90 nop e: 90 nop f: 90 nop 10: 90 nop 11: 90 nop 12: 90 nop 13: 90 nop 14: 90 nop 15: 90 nop 16: 90 nop 17: 90 nop 18: 90 nop 19: 90 nop 1a: 90 nop 1b: 90 nop 1c: 90 nop 1d: 48 89 cb mov %rcx,%rbx 20: 48 c1 fb 3f sar $0x3f,%rbx 24: 48 09 d9 or %rbx,%rcx 27: 0f 01 cb stac * 2a: 89 01 mov %eax,(%rcx) <-- trapping instruction 2c: 31 c9 xor %ecx,%ecx 2e: 0f 01 ca clac 31: e9 87 96 03 00 jmp 0x396bd 36: 90 nop 37: 90 nop 38: 90 nop 39: 90 nop 3a: 90 nop 3b: 90 nop 3c: 90 nop 3d: 90 nop 3e: 90 nop 3f: 90 nop