====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Tainted: G L ------------------------------------------------------ syz.4.1108/8287 is trying to acquire lock: ffff800088d6a500 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:316 [inline] ffff800088d6a500 (fs_reclaim){+.+.}-{0:0}, at: slab_pre_alloc_hook mm/slub.c:4636 [inline] ffff800088d6a500 (fs_reclaim){+.+.}-{0:0}, at: slab_alloc_node mm/slub.c:4974 [inline] ffff800088d6a500 (fs_reclaim){+.+.}-{0:0}, at: kmem_cache_alloc_noprof+0x60/0x5d4 mm/slub.c:5010 but task is already holding lock: ffff0000c70dbb90 (&q->blkcg_mutex){+.+.}-{4:4}, at: blkg_conf_prep+0xa0/0x934 block/blk-cgroup.c:849 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&q->blkcg_mutex){+.+.}-{4:4}: __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x164/0x1078 kernel/locking/mutex.c:821 mutex_lock_nested+0x24/0x30 kernel/locking/mutex.c:874 blkcg_activate_policy+0x1a0/0x7b0 block/blk-cgroup.c:1608 blk_throtl_init+0x2ac/0x3b0 block/blk-throttle.c:1339 tg_set_conf+0x1b0/0x46c block/blk-throttle.c:1368 tg_set_conf_u64+0x38/0x4c block/blk-throttle.c:1405 cgroup_file_write+0x23c/0x6e4 kernel/cgroup/cgroup.c:4412 kernfs_fop_write_iter+0x260/0x3b8 fs/kernfs/file.c:345 new_sync_write fs/read_write.c:595 [inline] vfs_write+0x51c/0xa0c fs/read_write.c:687 ksys_write+0x12c/0x228 fs/read_write.c:739 __do_sys_write fs/read_write.c:750 [inline] __se_sys_write fs/read_write.c:747 [inline] __arm64_sys_write+0x84/0x98 fs/read_write.c:747 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline] invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49 el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140 el0_svc+0x60/0x1d8 arch/arm64/kernel/entry-common.c:796 el0t_64_sync_handler+0x44/0x104 arch/arm64/kernel/entry-common.c:815 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:606 -> #1 (&q->q_usage_counter(io)#17){++++}-{0:0}: blk_alloc_queue+0x488/0x590 block/blk-core.c:504 blk_mq_alloc_queue+0x148/0x284 block/blk-mq.c:4431 __blk_mq_alloc_disk+0x38/0x10c block/blk-mq.c:4478 loop_add+0x358/0x8e4 drivers/block/loop.c:2073 loop_init+0xe8/0x10c drivers/block/loop.c:2312 do_one_initcall+0x274/0x9f8 init/main.c:1362 do_initcall_level+0x12c/0x1c4 init/main.c:1424 do_initcalls+0x70/0xd0 init/main.c:1440 do_basic_setup+0x7c/0x90 init/main.c:1460 kernel_init_freeable+0x258/0x398 init/main.c:1675 kernel_init+0x28/0x1e0 init/main.c:1565 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:854 -> #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+0x1660/0x2b08 kernel/locking/lockdep.c:5288 lock_acquire+0x13c/0x320 kernel/locking/lockdep.c:5942 __fs_reclaim_acquire mm/page_alloc.c:4375 [inline] fs_reclaim_acquire+0x90/0x110 mm/page_alloc.c:4389 might_alloc include/linux/sched/mm.h:316 [inline] slab_pre_alloc_hook mm/slub.c:4636 [inline] slab_alloc_node mm/slub.c:4974 [inline] kmem_cache_alloc_noprof+0x60/0x5d4 mm/slub.c:5010 __radix_tree_preload+0x2f4/0x844 lib/radix-tree.c:338 radix_tree_preload+0x38/0x54 lib/radix-tree.c:369 blkg_conf_prep+0x540/0x934 block/blk-cgroup.c:885 tg_set_conf+0x1e4/0x46c block/blk-throttle.c:1373 tg_set_conf_u64+0x38/0x4c block/blk-throttle.c:1405 cgroup_file_write+0x23c/0x6e4 kernel/cgroup/cgroup.c:4412 kernfs_fop_write_iter+0x260/0x3b8 fs/kernfs/file.c:345 new_sync_write fs/read_write.c:595 [inline] vfs_write+0x51c/0xa0c fs/read_write.c:687 ksys_write+0x12c/0x228 fs/read_write.c:739 __do_sys_write fs/read_write.c:750 [inline] __se_sys_write fs/read_write.c:747 [inline] __arm64_sys_write+0x84/0x98 fs/read_write.c:747 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline] invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49 el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140 el0_svc+0x60/0x1d8 arch/arm64/kernel/entry-common.c:796 el0t_64_sync_handler+0x44/0x104 arch/arm64/kernel/entry-common.c:815 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:606 other info that might help us debug this: Chain exists of: fs_reclaim --> &q->q_usage_counter(io)#17 --> &q->blkcg_mutex Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&q->blkcg_mutex); lock(&q->q_usage_counter(io)#17); lock(&q->blkcg_mutex); lock(fs_reclaim); *** DEADLOCK *** locks held by syz.4.1108/8287: 6, last CPU#0: #0: ffff0000d2fac7f0 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x100/0x144 fs/file.c:1259 #1: ffff0000d3e1c460 (sb_writers#9){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2753 [inline] #1: ffff0000d3e1c460 (sb_writers#9){.+.+}-{0:0}, at: vfs_write+0x248/0xa0c fs/read_write.c:683 #2: ffff0000c9d60080 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x1b0/0x3b8 fs/kernfs/file.c:336 #3: ffff0000ef9a84b8 (kn->active#72){.+.+}-{0:0}, at: kernfs_get_active_of fs/kernfs/file.c:73 [inline] #3: ffff0000ef9a84b8 (kn->active#72){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x1f0/0x3b8 fs/kernfs/file.c:337 #4: ffff0000c70dba10 (&q->rq_qos_mutex){+.+.}-{4:4}, at: blkg_conf_open_bdev+0x208/0x34c block/blk-cgroup.c:806 #5: ffff0000c70dbb90 (&q->blkcg_mutex){+.+.}-{4:4}, at: blkg_conf_prep+0xa0/0x934 block/blk-cgroup.c:849 stack backtrace: CPU: 0 UID: 0 PID: 8287 Comm: syz.4.1108 Tainted: G L syzkaller #0 PREEMPT Tainted: [L]=SOFTLOCKUP Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/23/2026 Call trace: show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C) __dump_stack+0x30/0x40 lib/dump_stack.c:94 dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120 dump_stack+0x1c/0x28 lib/dump_stack.c:129 print_circular_bug+0x328/0x330 kernel/locking/lockdep.c:2087 check_noncircular+0x158/0x174 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+0x1660/0x2b08 kernel/locking/lockdep.c:5288 lock_acquire+0x13c/0x320 kernel/locking/lockdep.c:5942 __fs_reclaim_acquire mm/page_alloc.c:4375 [inline] fs_reclaim_acquire+0x90/0x110 mm/page_alloc.c:4389 might_alloc include/linux/sched/mm.h:316 [inline] slab_pre_alloc_hook mm/slub.c:4636 [inline] slab_alloc_node mm/slub.c:4974 [inline] kmem_cache_alloc_noprof+0x60/0x5d4 mm/slub.c:5010 __radix_tree_preload+0x2f4/0x844 lib/radix-tree.c:338 radix_tree_preload+0x38/0x54 lib/radix-tree.c:369 blkg_conf_prep+0x540/0x934 block/blk-cgroup.c:885 tg_set_conf+0x1e4/0x46c block/blk-throttle.c:1373 tg_set_conf_u64+0x38/0x4c block/blk-throttle.c:1405 cgroup_file_write+0x23c/0x6e4 kernel/cgroup/cgroup.c:4412 kernfs_fop_write_iter+0x260/0x3b8 fs/kernfs/file.c:345 new_sync_write fs/read_write.c:595 [inline] vfs_write+0x51c/0xa0c fs/read_write.c:687 ksys_write+0x12c/0x228 fs/read_write.c:739 __do_sys_write fs/read_write.c:750 [inline] __se_sys_write fs/read_write.c:747 [inline] __arm64_sys_write+0x84/0x98 fs/read_write.c:747 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline] invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49 el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140 el0_svc+0x60/0x1d8 arch/arm64/kernel/entry-common.c:796 el0t_64_sync_handler+0x44/0x104 arch/arm64/kernel/entry-common.c:815 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:606