rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: 0-...!: (0 ticks this GP) idle=322/1/0x4000000000000000 softirq=51120/51120 fqs=0 (detected by 1, t=10502 jiffies, g=89325, q=4765) ============================================ WARNING: possible recursive locking detected 5.11.0-rc1-next-20210104-syzkaller #0 Not tainted -------------------------------------------- kworker/u4:0/9 is trying to acquire lock: ffffffff8b36bd58 (rcu_node_0){-.-.}-{2:2}, at: rcu_dump_cpu_stacks+0x9c/0x21e kernel/rcu/tree_stall.h:334 but task is already holding lock: ffffffff8b36bd58 (rcu_node_0){-.-.}-{2:2}, at: print_other_cpu_stall kernel/rcu/tree_stall.h:493 [inline] ffffffff8b36bd58 (rcu_node_0){-.-.}-{2:2}, at: check_cpu_stall kernel/rcu/tree_stall.h:652 [inline] ffffffff8b36bd58 (rcu_node_0){-.-.}-{2:2}, at: rcu_pending kernel/rcu/tree.c:3751 [inline] ffffffff8b36bd58 (rcu_node_0){-.-.}-{2:2}, at: rcu_sched_clock_irq.cold+0xbc/0xec3 kernel/rcu/tree.c:2580 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(rcu_node_0); lock(rcu_node_0); *** DEADLOCK *** May be due to missing lock nesting notation 7 locks held by kworker/u4:0/9: #0: ffff88814155c138 ((wq_completion)writeback){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline] #0: ffff88814155c138 ((wq_completion)writeback){+.+.}-{0:0}, at: atomic64_set include/asm-generic/atomic-instrumented.h:856 [inline] #0: ffff88814155c138 ((wq_completion)writeback){+.+.}-{0:0}, at: atomic_long_set include/asm-generic/atomic-long.h:41 [inline] #0: ffff88814155c138 ((wq_completion)writeback){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:616 [inline] #0: ffff88814155c138 ((wq_completion)writeback){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline] #0: ffff88814155c138 ((wq_completion)writeback){+.+.}-{0:0}, at: process_one_work+0x871/0x15f0 kernel/workqueue.c:2246 #1: ffffc90000ce7da8 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: process_one_work+0x8a5/0x15f0 kernel/workqueue.c:2250 #2: ffff888021af00e0 (&type->s_umount_key#41){++++}-{3:3}, at: trylock_super+0x1d/0x100 fs/super.c:418 #3: ffff888021af2a40 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: do_writepages+0xec/0x290 mm/page-writeback.c:2352 #4: ffff888031943848 (&mapping->i_mmap_rwsem){++++}-{3:3}, at: i_mmap_lock_read include/linux/fs.h:508 [inline] #4: ffff888031943848 (&mapping->i_mmap_rwsem){++++}-{3:3}, at: rmap_walk_file+0x6cc/0xbf0 mm/rmap.c:1925 #5: ffff888026fa5858 (ptlock_ptr(page)#2){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:354 [inline] #5: ffff888026fa5858 (ptlock_ptr(page)#2){+.+.}-{2:2}, at: map_pte mm/page_vma_mapped.c:51 [inline] #5: ffff888026fa5858 (ptlock_ptr(page)#2){+.+.}-{2:2}, at: page_vma_mapped_walk+0x120f/0x1c90 mm/page_vma_mapped.c:217 #6: ffffffff8b36bd58 (rcu_node_0){-.-.}-{2:2}, at: print_other_cpu_stall kernel/rcu/tree_stall.h:493 [inline] #6: ffffffff8b36bd58 (rcu_node_0){-.-.}-{2:2}, at: check_cpu_stall kernel/rcu/tree_stall.h:652 [inline] #6: ffffffff8b36bd58 (rcu_node_0){-.-.}-{2:2}, at: rcu_pending kernel/rcu/tree.c:3751 [inline] #6: ffffffff8b36bd58 (rcu_node_0){-.-.}-{2:2}, at: rcu_sched_clock_irq.cold+0xbc/0xec3 kernel/rcu/tree.c:2580 stack backtrace: CPU: 1 PID: 9 Comm: kworker/u4:0 Not tainted 5.11.0-rc1-next-20210104-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Workqueue: writeback wb_workfn (flush-8:0) Call Trace: __dump_stack lib/dump_stack.c:79 [inline] dump_stack+0x107/0x163 lib/dump_stack.c:120 print_deadlock_bug kernel/locking/lockdep.c:2761 [inline] check_deadlock kernel/locking/lockdep.c:2804 [inline] validate_chain kernel/locking/lockdep.c:3595 [inline] __lock_acquire.cold+0x15e/0x3b0 kernel/locking/lockdep.c:4832 lock_acquire kernel/locking/lockdep.c:5437 [inline] lock_acquire+0x29d/0x740 kernel/locking/lockdep.c:5402 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline] _raw_spin_lock_irqsave+0x39/0x50 kernel/locking/spinlock.c:159 rcu_dump_cpu_stacks+0x9c/0x21e kernel/rcu/tree_stall.h:334 print_other_cpu_stall kernel/rcu/tree_stall.h:510 [inline] check_cpu_stall kernel/rcu/tree_stall.h:652 [inline] rcu_pending kernel/rcu/tree.c:3751 [inline] rcu_sched_clock_irq.cold+0x6db/0xec3 kernel/rcu/tree.c:2580 update_process_times+0x16d/0x200 kernel/time/timer.c:1782 tick_sched_handle+0x9b/0x180 kernel/time/tick-sched.c:226 tick_sched_timer+0x1b0/0x2d0 kernel/time/tick-sched.c:1369 __run_hrtimer kernel/time/hrtimer.c:1519 [inline] __hrtimer_run_queues+0x1ce/0xea0 kernel/time/hrtimer.c:1583 hrtimer_interrupt+0x334/0x940 kernel/time/hrtimer.c:1645 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1085 [inline] __sysvec_apic_timer_interrupt+0x146/0x540 arch/x86/kernel/apic/apic.c:1102 asm_call_irq_on_stack+0xf/0x20 __run_sysvec_on_irqstack arch/x86/include/asm/irq_stack.h:37 [inline] run_sysvec_on_irqstack_cond arch/x86/include/asm/irq_stack.h:89 [inline] sysvec_apic_timer_interrupt+0xbd/0x100 arch/x86/kernel/apic/apic.c:1096 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:628 RIP: 0010:csd_lock_wait kernel/smp.c:227 [inline] RIP: 0010:smp_call_function_single+0x1b0/0x4b0 kernel/smp.c:512 Code: 10 8b 7c 24 1c 48 8d 74 24 40 48 89 44 24 50 48 8b 44 24 08 48 89 44 24 58 e8 0c fb ff ff 41 89 c5 eb 07 e8 82 43 0b 00 f3 90 <44> 8b 64 24 48 31 ff 41 83 e4 01 44 89 e6 e8 ed 4a 0b 00 45 85 e4 RSP: 0018:ffffc90000ce6c40 EFLAGS: 00000293 RAX: 0000000000000000 RBX: 1ffff9200019cd8c RCX: 0000000000000000 RDX: ffff888010d60000 RSI: ffffffff81673d8e RDI: 0000000000000003 RBP: ffffc90000ce6d08 R08: 0000000000000000 R09: 0000000000000000 R10: ffffffff81673da3 R11: 0000000000000000 R12: 0000000000000001 R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000008 smp_call_function_many_cond+0x25f/0x9d0 kernel/smp.c:648 on_each_cpu_cond_mask+0x50/0x160 kernel/smp.c:899 __flush_tlb_others arch/x86/include/asm/paravirt.h:74 [inline] flush_tlb_others arch/x86/mm/tlb.c:829 [inline] flush_tlb_mm_range+0x2ac/0x3d0 arch/x86/mm/tlb.c:916 flush_tlb_page arch/x86/include/asm/tlbflush.h:235 [inline] ptep_clear_flush+0x12b/0x160 mm/pgtable-generic.c:97 page_mkclean_one+0x351/0x610 mm/rmap.c:930 rmap_walk_file+0x562/0xbf0 mm/rmap.c:1935 rmap_walk+0x105/0x190 mm/rmap.c:1953 page_mkclean+0x21c/0x2b0 mm/rmap.c:998 clear_page_dirty_for_io+0x31c/0x9d0 mm/page-writeback.c:2698 mpage_submit_page+0x80/0x2a0 fs/ext4/inode.c:2081 mpage_process_page_bufs+0x656/0x780 fs/ext4/inode.c:2215 mpage_prepare_extent_to_map+0x904/0xe00 fs/ext4/inode.c:2627 ext4_writepages+0x95f/0x38a0 fs/ext4/inode.c:2755 do_writepages+0xec/0x290 mm/page-writeback.c:2352 __writeback_single_inode+0x122/0x1180 fs/fs-writeback.c:1461 writeback_sb_inodes+0x53d/0xef0 fs/fs-writeback.c:1721 __writeback_inodes_wb+0xc6/0x280 fs/fs-writeback.c:1790 wb_writeback+0x814/0xc40 fs/fs-writeback.c:1896 wb_check_old_data_flush fs/fs-writeback.c:1998 [inline] wb_do_writeback fs/fs-writeback.c:2051 [inline] wb_workfn+0x891/0x12d0 fs/fs-writeback.c:2080 process_one_work+0x98d/0x15f0 kernel/workqueue.c:2275 worker_thread+0x64c/0x1120 kernel/workqueue.c:2421 kthread+0x3b1/0x4a0 kernel/kthread.c:292 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296