====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Tainted: G L ------------------------------------------------------ syz.3.2666/12491 is trying to acquire lock: ffffffff90290820 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:316 [inline] ffffffff90290820 (fs_reclaim){+.+.}-{0:0}, at: slab_pre_alloc_hook mm/slub.c:4673 [inline] ffffffff90290820 (fs_reclaim){+.+.}-{0:0}, at: slab_alloc_node mm/slub.c:5011 [inline] ffffffff90290820 (fs_reclaim){+.+.}-{0:0}, at: __kmalloc_cache_noprof+0x61/0x600 mm/slub.c:5676 but task is already holding lock: ffff88807f1e8530 (&idev->mc_lock){+.+.}-{4:4}, at: __ipv6_dev_mc_inc+0x4e/0xaf0 net/ipv6/mcast.c:963 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #7 (&idev->mc_lock){+.+.}-{4:4}: __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x197/0x15a0 kernel/locking/mutex.c:821 __ipv6_dev_mc_inc+0x4e/0xaf0 net/ipv6/mcast.c:963 __ipv6_sock_mc_join+0x511/0x830 net/ipv6/mcast.c:234 ipv6_mcast_join_leave+0x1a2/0x240 net/ipv6/ipv6_sockglue.c:277 do_ipv6_setsockopt+0x1958/0x2960 net/ipv6/ipv6_sockglue.c:819 ipv6_setsockopt+0x59/0x170 net/ipv6/ipv6_sockglue.c:880 do_sock_setsockopt+0x17c/0x1b0 net/socket.c:2399 __sys_setsockopt net/socket.c:2424 [inline] __do_sys_setsockopt net/socket.c:2430 [inline] __se_sys_setsockopt net/socket.c:2427 [inline] __x64_sys_setsockopt+0x13d/0x1b0 net/socket.c:2427 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_INET6){+.+.}-{0:0}: lock_sock_nested+0x41/0x100 net/core/sock.c:3879 lock_sock include/net/sock.h:1715 [inline] inet_shutdown+0x6a/0x390 net/ipv4/af_inet.c:911 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:3495 [inline] process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3578 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3659 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+0x197/0x15a0 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:2131 __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+0x167/0x2f0 block/blk-mq.c:2546 process_one_work kernel/workqueue.c:3495 [inline] process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3578 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3659 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+0x197/0x15a0 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:2131 __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+0x167/0x2f0 block/blk-mq.c:2546 process_one_work kernel/workqueue.c:3495 [inline] process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3578 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3659 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:225 [inline] __synchronize_srcu+0xca/0x2f0 kernel/rcu/srcutree.c:1662 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:801 [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:1360 do_initcall_level+0x10a/0x1a0 init/main.c:1422 do_initcalls+0x59/0xa0 init/main.c:1438 kernel_init_freeable+0x29d/0x3e0 init/main.c:1673 kernel_init+0x22/0x1d0 init/main.c:1563 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+0x197/0x15a0 kernel/locking/mutex.c:821 elevator_change+0x1af/0x480 block/elevator.c:679 elv_iosched_store+0x504/0x630 block/elevator.c:826 queue_attr_store+0x207/0x2b0 block/blk-sysfs.c:906 kernfs_fop_write_iter+0x3a4/0x540 fs/kernfs/file.c:345 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:1036 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)#66){++++}-{0:0}: blk_alloc_queue+0x544/0x690 block/blk-core.c:505 blk_mq_alloc_queue block/blk-mq.c:4432 [inline] __blk_mq_alloc_disk+0x194/0x390 block/blk-mq.c:4479 null_add_dev+0xe82/0x1d70 drivers/block/null_blk/main.c:2017 null_create_dev drivers/block/null_blk/main.c:2114 [inline] null_init+0x1e3/0x390 drivers/block/null_blk/main.c:2178 do_one_initcall+0x250/0x870 init/main.c:1360 do_initcall_level+0x10a/0x1a0 init/main.c:1422 do_initcalls+0x59/0xa0 init/main.c:1438 kernel_init_freeable+0x29d/0x3e0 init/main.c:1673 kernel_init+0x22/0x1d0 init/main.c:1563 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:4381 [inline] fs_reclaim_acquire+0x71/0x100 mm/page_alloc.c:4395 might_alloc include/linux/sched/mm.h:316 [inline] slab_pre_alloc_hook mm/slub.c:4673 [inline] slab_alloc_node mm/slub.c:5011 [inline] __kmalloc_cache_noprof+0x61/0x600 mm/slub.c:5676 _kmalloc_noprof include/linux/slab.h:991 [inline] _kzalloc_noprof include/linux/slab.h:1312 [inline] mca_alloc net/ipv6/mcast.c:890 [inline] __ipv6_dev_mc_inc+0x447/0xaf0 net/ipv6/mcast.c:981 ipv6_add_dev+0xe6d/0x1400 net/ipv6/addrconf.c:475 addrconf_notify+0x771/0x1050 net/ipv6/addrconf.c:3689 notifier_call_chain+0x1a5/0x3d0 kernel/notifier.c:86 call_netdevice_notifiers_extack net/core/dev.c:2351 [inline] call_netdevice_notifiers net/core/dev.c:2365 [inline] register_netdevice+0x1bfe/0x2280 net/core/dev.c:11640 ppp_unit_register drivers/net/ppp/ppp_generic.c:1217 [inline] ppp_dev_configure+0x806/0xaa0 drivers/net/ppp/ppp_generic.c:1277 ppp_create_interface drivers/net/ppp/ppp_generic.c:3378 [inline] ppp_unattached_ioctl drivers/net/ppp/ppp_generic.c:1062 [inline] ppp_ioctl+0xaff/0x1c00 drivers/net/ppp/ppp_generic.c:729 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_INET6 --> &idev->mc_lock Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&idev->mc_lock); lock(sk_lock-AF_INET6); lock(&idev->mc_lock); lock(fs_reclaim); *** DEADLOCK *** locks held by syz.3.2666/12491: 3, last CPU#0: #0: ffffffff90e2d600 (ppp_mutex){+.+.}-{4:4}, at: ppp_ioctl+0xdf/0x1c00 drivers/net/ppp/ppp_generic.c:725 #1: ffffffff9167d760 (rtnl_mutex){+.+.}-{4:4}, at: ppp_create_interface drivers/net/ppp/ppp_generic.c:3376 [inline] #1: ffffffff9167d760 (rtnl_mutex){+.+.}-{4:4}, at: ppp_unattached_ioctl drivers/net/ppp/ppp_generic.c:1062 [inline] #1: ffffffff9167d760 (rtnl_mutex){+.+.}-{4:4}, at: ppp_ioctl+0xaef/0x1c00 drivers/net/ppp/ppp_generic.c:729 #2: ffff88807f1e8530 (&idev->mc_lock){+.+.}-{4:4}, at: __ipv6_dev_mc_inc+0x4e/0xaf0 net/ipv6/mcast.c:963 stack backtrace: CPU: 0 UID: 0 PID: 12491 Comm: syz.3.2666 Tainted: G L syzkaller #0 PREEMPT(full) Tainted: [L]=SOFTLOCKUP Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026 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:4381 [inline] fs_reclaim_acquire+0x71/0x100 mm/page_alloc.c:4395 might_alloc include/linux/sched/mm.h:316 [inline] slab_pre_alloc_hook mm/slub.c:4673 [inline] slab_alloc_node mm/slub.c:5011 [inline] __kmalloc_cache_noprof+0x61/0x600 mm/slub.c:5676 _kmalloc_noprof include/linux/slab.h:991 [inline] _kzalloc_noprof include/linux/slab.h:1312 [inline] mca_alloc net/ipv6/mcast.c:890 [inline] __ipv6_dev_mc_inc+0x447/0xaf0 net/ipv6/mcast.c:981 ipv6_add_dev+0xe6d/0x1400 net/ipv6/addrconf.c:475 addrconf_notify+0x771/0x1050 net/ipv6/addrconf.c:3689 notifier_call_chain+0x1a5/0x3d0 kernel/notifier.c:86 call_netdevice_notifiers_extack net/core/dev.c:2351 [inline] call_netdevice_notifiers net/core/dev.c:2365 [inline] register_netdevice+0x1bfe/0x2280 net/core/dev.c:11640 ppp_unit_register drivers/net/ppp/ppp_generic.c:1217 [inline] ppp_dev_configure+0x806/0xaa0 drivers/net/ppp/ppp_generic.c:1277 ppp_create_interface drivers/net/ppp/ppp_generic.c:3378 [inline] ppp_unattached_ioctl drivers/net/ppp/ppp_generic.c:1062 [inline] ppp_ioctl+0xaff/0x1c00 drivers/net/ppp/ppp_generic.c:729 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: 0033:0x7fc2cb59e1d9 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:00007fc2cc46e028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 00007fc2cb825fa0 RCX: 00007fc2cb59e1d9 RDX: 00002000000000c0 RSI: 00000000c004743e RDI: 0000000000000003 RBP: 00007fc2cb635888 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007fc2cb826038 R14: 00007fc2cb825fa0 R15: 00007ffff8fac078