====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Tainted: G L ------------------------------------------------------ syz.3.201/6369 is trying to acquire lock: ffffffff8e2d05f8 (pcpu_alloc_mutex){+.+.}-{4:4}, at: pcpu_alloc_noprof+0x239/0x1920 mm/percpu.c:1848 but task is already holding lock: ffff888025d65120 (&q->q_usage_counter(io)#17){++++}-{0:0}, at: blk_mq_freeze_queue include/linux/blk-mq.h:956 [inline] ffff888025d65120 (&q->q_usage_counter(io)#17){++++}-{0:0}, at: blk_throtl_init+0x279/0x410 block/blk-throttle.c:1323 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&q->q_usage_counter(io)#17){++++}-{0:0}: blk_alloc_queue+0x54e/0x690 block/blk-core.c:460 blk_mq_alloc_queue block/blk-mq.c:4453 [inline] __blk_mq_alloc_disk+0x197/0x390 block/blk-mq.c:4500 loop_add+0x482/0xb50 drivers/block/loop.c:2065 loop_init+0xd9/0x170 drivers/block/loop.c:2304 do_one_initcall+0x250/0x870 init/main.c:1347 do_initcall_level+0x104/0x190 init/main.c:1409 do_initcalls+0x59/0xa0 init/main.c:1425 kernel_init_freeable+0x2a6/0x3e0 init/main.c:1658 kernel_init+0x1d/0x1d0 init/main.c:1548 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #1 (fs_reclaim){+.+.}-{0:0}: __fs_reclaim_acquire mm/page_alloc.c:4325 [inline] fs_reclaim_acquire+0x71/0x100 mm/page_alloc.c:4339 might_alloc include/linux/sched/mm.h:317 [inline] slab_pre_alloc_hook mm/slub.c:4534 [inline] slab_alloc_node mm/slub.c:4889 [inline] __do_kmalloc_node mm/slub.c:5308 [inline] __kmalloc_noprof+0x9d/0x7b0 mm/slub.c:5322 _kmalloc_noprof include/linux/slab.h:971 [inline] _kzalloc_noprof include/linux/slab.h:1284 [inline] pcpu_mem_zalloc mm/percpu.c:510 [inline] pcpu_alloc_chunk mm/percpu.c:1496 [inline] pcpu_create_chunk+0x54/0xcd0 mm/percpu-vm.c:338 pcpu_alloc_noprof+0x73d/0x1920 mm/percpu.c:1904 do_kmem_cache_create+0x11a/0x9a0 mm/slub.c:8545 create_cache mm/slab_common.c:252 [inline] __kmem_cache_create_args+0x31d/0x450 mm/slab_common.c:380 user_namespaces_init+0xb0/0x130 kernel/user_namespace.c:1411 do_one_initcall+0x250/0x870 init/main.c:1347 do_initcall_level+0x104/0x190 init/main.c:1409 do_initcalls+0x59/0xa0 init/main.c:1425 kernel_init_freeable+0x2a6/0x3e0 init/main.c:1658 kernel_init+0x1d/0x1d0 init/main.c:1548 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 (pcpu_alloc_mutex){+.+.}-{4:4}: check_prev_add kernel/locking/lockdep.c:3167 [inline] check_prevs_add kernel/locking/lockdep.c:3286 [inline] validate_chain kernel/locking/lockdep.c:3910 [inline] __lock_acquire+0x15a5/0x2d10 kernel/locking/lockdep.c:5239 lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5870 __mutex_lock_common kernel/locking/rtmutex_api.c:559 [inline] _mutex_lock_killable+0x63/0x1d0 kernel/locking/rtmutex_api.c:599 pcpu_alloc_noprof+0x239/0x1920 mm/percpu.c:1848 __percpu_counter_init_many+0x43/0x370 lib/percpu_counter.c:198 blkg_rwstat_init+0x2c/0x170 block/blk-cgroup-rwstat.c:12 throtl_pd_alloc+0xb6/0x460 block/blk-throttle.c:271 blkcg_activate_policy+0x692/0xb40 block/blk-cgroup.c:1647 blk_throtl_init+0x2f6/0x410 block/blk-throttle.c:1330 tg_set_conf+0x1d6/0x4c0 block/blk-throttle.c:1359 cgroup_file_write+0x331/0x8f0 kernel/cgroup/cgroup.c:4289 kernfs_fop_write_iter+0x3b0/0x540 fs/kernfs/file.c:352 new_sync_write fs/read_write.c:595 [inline] vfs_write+0x629/0xba0 fs/read_write.c:688 ksys_write+0x156/0x270 fs/read_write.c:740 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f other info that might help us debug this: Chain exists of: pcpu_alloc_mutex --> fs_reclaim --> &q->q_usage_counter(io)#17 Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&q->q_usage_counter(io)#17); lock(fs_reclaim); lock(&q->q_usage_counter(io)#17); lock(pcpu_alloc_mutex); *** DEADLOCK *** 7 locks held by syz.3.201/6369: #0: ffff888036ee4128 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x252/0x320 fs/file.c:1260 #1: ffff88802c0c2480 (sb_writers#10){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2733 [inline] #1: ffff88802c0c2480 (sb_writers#10){.+.+}-{0:0}, at: vfs_write+0x22d/0xba0 fs/read_write.c:684 #2: ffff88805c32e078 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x1df/0x540 fs/kernfs/file.c:343 #3: ffff888033e12788 (kn->active#66){.+.+}-{0:0}, at: kernfs_get_active_of fs/kernfs/file.c:80 [inline] #3: ffff888033e12788 (kn->active#66){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x232/0x540 fs/kernfs/file.c:344 #4: ffff888025d65358 (&q->rq_qos_mutex){+.+.}-{4:4}, at: blkg_conf_open_bdev+0x2b0/0x3c0 block/blk-cgroup.c:805 #5: ffff888025d65120 (&q->q_usage_counter(io)#17){++++}-{0:0}, at: blk_mq_freeze_queue include/linux/blk-mq.h:956 [inline] #5: ffff888025d65120 (&q->q_usage_counter(io)#17){++++}-{0:0}, at: blk_throtl_init+0x279/0x410 block/blk-throttle.c:1323 #6: ffff888025d65158 (&q->q_usage_counter(queue)){+.+.}-{0:0}, at: blk_mq_freeze_queue include/linux/blk-mq.h:956 [inline] #6: ffff888025d65158 (&q->q_usage_counter(queue)){+.+.}-{0:0}, at: blk_throtl_init+0x279/0x410 block/blk-throttle.c:1323 stack backtrace: CPU: 1 UID: 0 PID: 6369 Comm: syz.3.201 Tainted: G L syzkaller #0 PREEMPT_{RT,(full)} Tainted: [L]=SOFTLOCKUP Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026 Call Trace: dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120 print_circular_bug+0x2e1/0x300 kernel/locking/lockdep.c:2045 check_noncircular+0x12e/0x150 kernel/locking/lockdep.c:2177 check_prev_add kernel/locking/lockdep.c:3167 [inline] check_prevs_add kernel/locking/lockdep.c:3286 [inline] validate_chain kernel/locking/lockdep.c:3910 [inline] __lock_acquire+0x15a5/0x2d10 kernel/locking/lockdep.c:5239 lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5870 __mutex_lock_common kernel/locking/rtmutex_api.c:559 [inline] _mutex_lock_killable+0x63/0x1d0 kernel/locking/rtmutex_api.c:599 pcpu_alloc_noprof+0x239/0x1920 mm/percpu.c:1848 __percpu_counter_init_many+0x43/0x370 lib/percpu_counter.c:198 blkg_rwstat_init+0x2c/0x170 block/blk-cgroup-rwstat.c:12 throtl_pd_alloc+0xb6/0x460 block/blk-throttle.c:271 blkcg_activate_policy+0x692/0xb40 block/blk-cgroup.c:1647 blk_throtl_init+0x2f6/0x410 block/blk-throttle.c:1330 tg_set_conf+0x1d6/0x4c0 block/blk-throttle.c:1359 cgroup_file_write+0x331/0x8f0 kernel/cgroup/cgroup.c:4289 kernfs_fop_write_iter+0x3b0/0x540 fs/kernfs/file.c:352 new_sync_write fs/read_write.c:595 [inline] vfs_write+0x629/0xba0 fs/read_write.c:688 ksys_write+0x156/0x270 fs/read_write.c:740 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7fbd484bce59 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:00007fbd4670e028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 00007fbd48735fa0 RCX: 00007fbd484bce59 RDX: 000000000000006a RSI: 00002000000000c0 RDI: 0000000000000005 RBP: 00007fbd4670e090 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001 R13: 00007fbd48736038 R14: 00007fbd48735fa0 R15: 00007fffd839fdd8