rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: 0-...!: (1 GPs behind) idle=562/1/0x4000000000000000 softirq=67304/67305 fqs=216 (detected by 1, t=10502 jiffies, g=119437, q=1287) ============================================ WARNING: possible recursive locking detected 5.9.0-rc8-next-20201007-syzkaller #0 Not tainted -------------------------------------------- kworker/u4:17/13789 is trying to acquire lock: ffffffff8a55d3d8 (rcu_node_0){-.-.}-{2:2}, at: rcu_dump_cpu_stacks+0x9c/0x21e kernel/rcu/tree_stall.h:334 but task is already holding lock: ffffffff8a55d3d8 (rcu_node_0){-.-.}-{2:2}, at: print_other_cpu_stall kernel/rcu/tree_stall.h:493 [inline] ffffffff8a55d3d8 (rcu_node_0){-.-.}-{2:2}, at: check_cpu_stall kernel/rcu/tree_stall.h:652 [inline] ffffffff8a55d3d8 (rcu_node_0){-.-.}-{2:2}, at: rcu_pending kernel/rcu/tree.c:3705 [inline] ffffffff8a55d3d8 (rcu_node_0){-.-.}-{2:2}, at: rcu_sched_clock_irq.cold+0xbc/0xec3 kernel/rcu/tree.c:2575 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/u4:17/13789: #0: ffff888011902938 ((wq_completion)writeback){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline] #0: ffff888011902938 ((wq_completion)writeback){+.+.}-{0:0}, at: atomic64_set include/asm-generic/atomic-instrumented.h:856 [inline] #0: ffff888011902938 ((wq_completion)writeback){+.+.}-{0:0}, at: atomic_long_set include/asm-generic/atomic-long.h:41 [inline] #0: ffff888011902938 ((wq_completion)writeback){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:616 [inline] #0: ffff888011902938 ((wq_completion)writeback){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline] #0: ffff888011902938 ((wq_completion)writeback){+.+.}-{0:0}, at: process_one_work+0x821/0x15a0 kernel/workqueue.c:2240 #1: ffffc90004db7da8 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: process_one_work+0x854/0x15a0 kernel/workqueue.c:2244 #2: ffff8880209d00e0 (&type->s_umount_key#37){++++}-{3:3}, at: trylock_super+0x1d/0x100 fs/super.c:418 #3: ffff8880209d2a40 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: do_writepages+0xec/0x290 mm/page-writeback.c:2352 #4: ffff8880307a6b48 (&mapping->i_mmap_rwsem){++++}-{3:3}, at: i_mmap_lock_read include/linux/fs.h:508 [inline] #4: ffff8880307a6b48 (&mapping->i_mmap_rwsem){++++}-{3:3}, at: rmap_walk_file+0x6cc/0xbf0 mm/rmap.c:1923 #5: ffff8880255b0d38 (ptlock_ptr(page)#2){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:354 [inline] #5: ffff8880255b0d38 (ptlock_ptr(page)#2){+.+.}-{2:2}, at: map_pte mm/page_vma_mapped.c:51 [inline] #5: ffff8880255b0d38 (ptlock_ptr(page)#2){+.+.}-{2:2}, at: page_vma_mapped_walk+0x1618/0x2370 mm/page_vma_mapped.c:216 #6: ffffffff8a55d3d8 (rcu_node_0){-.-.}-{2:2}, at: print_other_cpu_stall kernel/rcu/tree_stall.h:493 [inline] #6: ffffffff8a55d3d8 (rcu_node_0){-.-.}-{2:2}, at: check_cpu_stall kernel/rcu/tree_stall.h:652 [inline] #6: ffffffff8a55d3d8 (rcu_node_0){-.-.}-{2:2}, at: rcu_pending kernel/rcu/tree.c:3705 [inline] #6: ffffffff8a55d3d8 (rcu_node_0){-.-.}-{2:2}, at: rcu_sched_clock_irq.cold+0xbc/0xec3 kernel/rcu/tree.c:2575 stack backtrace: CPU: 1 PID: 13789 Comm: kworker/u4:17 Not tainted 5.9.0-rc8-next-20201007-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:77 [inline] dump_stack+0x198/0x1fb lib/dump_stack.c:118 print_deadlock_bug kernel/locking/lockdep.c:2735 [inline] check_deadlock kernel/locking/lockdep.c:2776 [inline] validate_chain kernel/locking/lockdep.c:3567 [inline] __lock_acquire.cold+0x12e/0x3ad kernel/locking/lockdep.c:4817 lock_acquire+0x1f2/0xaa0 kernel/locking/lockdep.c:5419 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline] _raw_spin_lock_irqsave+0x94/0xd0 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:3705 [inline] rcu_sched_clock_irq.cold+0x6db/0xec3 kernel/rcu/tree.c:2575 update_process_times+0x25/0xa0 kernel/time/timer.c:1712 tick_sched_handle+0x9b/0x180 kernel/time/tick-sched.c:176 tick_sched_timer+0x1d1/0x2a0 kernel/time/tick-sched.c:1328 __run_hrtimer kernel/time/hrtimer.c:1524 [inline] __hrtimer_run_queues+0x1ce/0xea0 kernel/time/hrtimer.c:1588 hrtimer_interrupt+0x334/0x940 kernel/time/hrtimer.c:1650 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1080 [inline] __sysvec_apic_timer_interrupt+0x146/0x540 arch/x86/kernel/apic/apic.c:1097 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+0xb2/0xf0 arch/x86/kernel/apic/apic.c:1091 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:631 RIP: 0010:csd_lock_wait kernel/smp.c:227 [inline] RIP: 0010:smp_call_function_single+0x197/0x500 kernel/smp.c:512 Code: 48 8d 74 24 40 48 89 44 24 50 48 8b 44 24 08 48 89 44 24 58 e8 2a fa ff ff 41 89 c5 eb 07 e8 70 38 0b 00 f3 90 44 8b 64 24 48 <31> ff 41 83 e4 01 44 89 e6 e8 bb 34 0b 00 45 85 e4 75 e1 e8 51 38 RSP: 0018:ffffc90004db6c40 EFLAGS: 00000293 RAX: 0000000000000000 RBX: 1ffff920009b6d8c RCX: ffffffff816a2035 RDX: ffff888011ffe380 RSI: ffffffff816a2020 RDI: 0000000000000005 RBP: ffffc90004db6d08 R08: 0000000000000001 R09: ffff8880ae437047 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000011 R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000040 smp_call_function_many_cond+0x1a4/0xa10 kernel/smp.c:648 on_each_cpu_cond_mask+0x50/0x240 kernel/smp.c:899 __flush_tlb_others arch/x86/include/asm/paravirt.h:74 [inline] flush_tlb_others arch/x86/mm/tlb.c:899 [inline] flush_tlb_mm_range+0x2ad/0x530 arch/x86/mm/tlb.c:986 flush_tlb_page arch/x86/include/asm/tlbflush.h:235 [inline] ptep_clear_flush+0x12b/0x160 mm/pgtable-generic.c:97 page_mkclean_one+0x381/0x690 mm/rmap.c:930 rmap_walk_file+0x562/0xbf0 mm/rmap.c:1933 rmap_walk+0x105/0x190 mm/rmap.c:1951 page_mkclean+0x21c/0x2b0 mm/rmap.c:998 clear_page_dirty_for_io+0x31c/0x920 mm/page-writeback.c:2698 mpage_submit_page+0x80/0x2c0 fs/ext4/inode.c:2061 mpage_process_page_bufs+0x656/0x780 fs/ext4/inode.c:2195 mpage_prepare_extent_to_map+0x904/0xe00 fs/ext4/inode.c:2607 ext4_writepages+0x909/0x37f0 fs/ext4/inode.c:2735 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+0x933/0x15a0 kernel/workqueue.c:2269 worker_thread+0x64c/0x1120 kernel/workqueue.c:2415 kthread+0x3af/0x4a0 kernel/kthread.c:292 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296