rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: 0-...!: (0 ticks this GP) idle=876/1/0x4000000000000000 softirq=48539/48539 fqs=1173 (detected by 1, t=10502 jiffies, g=72013, q=4092) ============================================ WARNING: possible recursive locking detected 5.10.0-rc4-syzkaller #0 Not tainted -------------------------------------------- kworker/u4:2/47 is trying to acquire lock: ffffffff8baea698 (rcu_node_0){-.-.}-{2:2}, at: rcu_dump_cpu_stacks+0x96/0x2b0 kernel/rcu/tree_stall.h:328 but task is already holding lock: ffffffff8baea698 (rcu_node_0){-.-.}-{2:2}, at: print_other_cpu_stall kernel/rcu/tree_stall.h:487 [inline] ffffffff8baea698 (rcu_node_0){-.-.}-{2:2}, at: check_cpu_stall kernel/rcu/tree_stall.h:646 [inline] ffffffff8baea698 (rcu_node_0){-.-.}-{2:2}, at: rcu_pending kernel/rcu/tree.c:3694 [inline] ffffffff8baea698 (rcu_node_0){-.-.}-{2:2}, at: rcu_sched_clock_irq+0xd31/0x2280 kernel/rcu/tree.c:2567 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/u4:2/47: #0: ffff8880147a1938 ((wq_completion)writeback){+.+.}-{0:0}, at: process_one_work+0x6f4/0xfc0 kernel/workqueue.c:2245 #1: ffffc90000ecfd80 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: process_one_work+0x733/0xfc0 kernel/workqueue.c:2247 #2: ffff8880223040e0 (&type->s_umount_key#39){++++}-{3:3}, at: trylock_super+0x1b/0xf0 fs/super.c:418 #3: ffff888022306a40 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: do_writepages+0xda/0x1f0 mm/page-writeback.c:2352 #4: ffff88802f973848 (&mapping->i_mmap_rwsem){++++}-{3:3}, at: i_mmap_lock_read include/linux/fs.h:508 [inline] #4: ffff88802f973848 (&mapping->i_mmap_rwsem){++++}-{3:3}, at: rmap_walk_file+0x2b3/0x740 mm/rmap.c:1920 #5: ffff88801a7d1498 (ptlock_ptr(page)#2){+.+.}-{2:2}, at: page_vma_mapped_walk+0xbbd/0x1850 mm/page_vma_mapped.c:50 #6: ffffffff8baea698 (rcu_node_0){-.-.}-{2:2}, at: print_other_cpu_stall kernel/rcu/tree_stall.h:487 [inline] #6: ffffffff8baea698 (rcu_node_0){-.-.}-{2:2}, at: check_cpu_stall kernel/rcu/tree_stall.h:646 [inline] #6: ffffffff8baea698 (rcu_node_0){-.-.}-{2:2}, at: rcu_pending kernel/rcu/tree.c:3694 [inline] #6: ffffffff8baea698 (rcu_node_0){-.-.}-{2:2}, at: rcu_sched_clock_irq+0xd31/0x2280 kernel/rcu/tree.c:2567 stack backtrace: CPU: 1 PID: 47 Comm: kworker/u4:2 Not tainted 5.10.0-rc4-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+0x137/0x1be lib/dump_stack.c:118 __lock_acquire+0x2466/0x6210 kernel/locking/lockdep.c:4668 lock_acquire+0x114/0x5e0 kernel/locking/lockdep.c:5435 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline] _raw_spin_lock_irqsave+0x73/0xa0 kernel/locking/spinlock.c:159 rcu_dump_cpu_stacks+0x96/0x2b0 kernel/rcu/tree_stall.h:328 print_other_cpu_stall kernel/rcu/tree_stall.h:504 [inline] check_cpu_stall kernel/rcu/tree_stall.h:646 [inline] rcu_pending kernel/rcu/tree.c:3694 [inline] rcu_sched_clock_irq+0x19c1/0x2280 kernel/rcu/tree.c:2567 update_process_times+0x197/0x200 kernel/time/timer.c:1709 tick_sched_handle kernel/time/tick-sched.c:176 [inline] tick_sched_timer+0x25e/0x410 kernel/time/tick-sched.c:1328 __run_hrtimer kernel/time/hrtimer.c:1519 [inline] __hrtimer_run_queues+0x43d/0x960 kernel/time/hrtimer.c:1583 hrtimer_interrupt+0x3b3/0xe00 kernel/time/hrtimer.c:1645 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1080 [inline] __sysvec_apic_timer_interrupt+0xf9/0x270 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+0x9f/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+0x222/0x4d0 kernel/smp.c:512 Code: 44 8b 6c 24 28 44 89 ee 83 e6 01 31 ff e8 86 36 0b 00 41 83 e5 01 75 10 e8 6b 32 0b 00 e9 0d 01 00 00 66 0f 1f 44 00 00 f3 90 <42> 0f b6 04 23 84 c0 75 15 f7 44 24 28 01 00 00 00 0f 84 e9 00 00 RSP: 0018:ffffc90000ecee20 EFLAGS: 00000293 RAX: ffffffff8169ee7e RBX: 1ffff920001d9dc9 RCX: ffff888011429a40 RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000 RBP: ffffc90000eceed8 R08: ffffffff8169ee4a R09: fffffbfff1d93263 R10: fffffbfff1d93263 R11: 0000000000000000 R12: dffffc0000000000 R13: 0000000000000001 R14: ffffc90000ecee48 R15: 0000000000000000 smp_call_function_many_cond+0x922/0xa40 kernel/smp.c:648 on_each_cpu_cond_mask+0x65/0x1a0 kernel/smp.c:899 __flush_tlb_others arch/x86/include/asm/paravirt.h:74 [inline] flush_tlb_others arch/x86/mm/tlb.c:823 [inline] flush_tlb_mm_range+0x29f/0x390 arch/x86/mm/tlb.c:910 flush_tlb_page arch/x86/include/asm/tlbflush.h:235 [inline] ptep_clear_flush+0x111/0x150 mm/pgtable-generic.c:97 page_mkclean_one+0x3ec/0x710 mm/rmap.c:930 rmap_walk_file+0x40d/0x740 mm/rmap.c:1930 rmap_walk mm/rmap.c:1948 [inline] page_mkclean+0x2b9/0x3d0 mm/rmap.c:998 clear_page_dirty_for_io+0x2fb/0xb70 mm/page-writeback.c:2698 mpage_submit_page+0x89/0x230 fs/ext4/inode.c:2072 mpage_process_page_bufs+0x6c2/0x810 fs/ext4/inode.c:2206 mpage_prepare_extent_to_map+0x982/0xd40 fs/ext4/inode.c:2618 ext4_writepages+0xc4d/0x3b50 fs/ext4/inode.c:2746 do_writepages+0xda/0x1f0 mm/page-writeback.c:2352 __writeback_single_inode+0xcc/0x640 fs/fs-writeback.c:1461 writeback_sb_inodes+0x8ee/0x1810 fs/fs-writeback.c:1721 __writeback_inodes_wb fs/fs-writeback.c:1790 [inline] wb_writeback+0x483/0x900 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+0x96d/0x1200 fs/fs-writeback.c:2080 process_one_work+0x789/0xfc0 kernel/workqueue.c:2272 worker_thread+0xaa4/0x1460 kernel/workqueue.c:2418 kthread+0x36b/0x390 kernel/kthread.c:292 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296