Lockdep warning on io_file_data_ref_zero() with 5.10-rc5

[Nadav Amit <nadav.amit@gmail.com>]

Hello Pavel,

I got the following lockdep splat while rebasing my work on 5.10-rc5 on the
kernel (based on 5.10-rc5+).

I did not actually confirm that the problem is triggered without my changes,
as my iouring workload requires some kernel changes (not iouring changes),
yet IMHO it seems pretty clear that this is a result of your commit
e297822b20e7f ("io_uring: order refnode recycling”), that acquires a lock in
io_file_data_ref_zero() inside a softirq context.

Let me know if my analysis is wrong.

Regards,
Nadav

[  136.349353] ================================
[  136.350212] WARNING: inconsistent lock state
[  136.351093] 5.10.0-rc5+ #1435 Not tainted
[  136.352003] --------------------------------
[  136.352891] inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
[  136.354057] swapper/5/0 [HC0[0]:SC1[1]:HE1:SE0] takes:
[  136.355078] ffff88810417d6a8 (&file_data->lock){+.?.}-{2:2}, at: io_file_data_ref_zero+0x4d/0x220
[  136.356717] {SOFTIRQ-ON-W} state was registered at:
[  136.357539]   lock_acquire+0x172/0x520
[  136.358209]   _raw_spin_lock+0x30/0x40
[  136.358880]   __io_uring_register+0x1c99/0x1fe0
[  136.359656]   __x64_sys_io_uring_register+0xe2/0x270
[  136.360489]   do_syscall_64+0x39/0x90
[  136.361144]   entry_SYSCALL_64_after_hwframe+0x44/0xa9
[  136.361991] irq event stamp: 835836
[  136.362627] hardirqs last  enabled at (835836): [<ffffffff82856721>] _raw_spin_unlock_irqrestore+0x41/0x50
[  136.364112] hardirqs last disabled at (835835): [<ffffffff828564ca>] _raw_spin_lock_irqsave+0x5a/0x60
[  136.365553] softirqs last  enabled at (835824): [<ffffffff810cfa71>] _local_bh_enable+0x21/0x40
[  136.366920] softirqs last disabled at (835825): [<ffffffff82a01022>] asm_call_irq_on_stack+0x12/0x20
[  136.368335] 
[  136.368335] other info that might help us debug this:
[  136.369414]  Possible unsafe locking scenario:
[  136.369414] 
[  136.370414]        CPU0
[  136.370907]        ----
[  136.371403]   lock(&file_data->lock);
[  136.372064]   <Interrupt>
[  136.372585]     lock(&file_data->lock);
[  136.373269] 
[  136.373269]  *** DEADLOCK ***
[  136.373269] 
[  136.374319] 2 locks held by swapper/5/0:
[  136.375005]  #0: ffffffff83c45380 (rcu_callback){....}-{0:0}, at: rcu_core+0x451/0xb70
[  136.376284]  #1: ffffffff83c454a0 (rcu_read_lock){....}-{1:2}, at: percpu_ref_switch_to_atomic_rcu+0x139/0x320
[  136.377849] 
[  136.377849] stack backtrace:
[  136.378650] CPU: 5 PID: 0 Comm: swapper/5 Not tainted 5.10.0-rc5irina+ #1435
[  136.379746] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.11.0-0-g63451fca13-prebuilt.qemu-project.org 04/01/2014
[  136.381550] Call Trace:
[  136.382053]  <IRQ>
[  136.382502]  dump_stack+0xa4/0xd9
[  136.383116]  print_usage_bug.cold+0x217/0x220
[  136.383871]  mark_lock+0xb90/0xe80
[  136.384506]  ? print_usage_bug+0x180/0x180
[  136.385223]  ? __kasan_check_read+0x11/0x20
[  136.385946]  ? mark_lock+0x116/0xe80
[  136.386599]  ? print_usage_bug+0x180/0x180
[  136.387324]  ? __lock_acquire+0x8f5/0x2a80
[  136.388039]  ? __kasan_check_read+0x11/0x20
[  136.388776]  ? __lock_acquire+0x8f5/0x2a80
[  136.389493]  __lock_acquire+0xdc9/0x2a80
[  136.390190]  ? lockdep_hardirqs_on_prepare+0x210/0x210
[  136.391039]  ? rcu_read_lock_sched_held+0xa1/0xd0
[  136.391835]  ? rcu_read_lock_bh_held+0xb0/0xb0
[  136.392603]  lock_acquire+0x172/0x520
[  136.393258]  ? io_file_data_ref_zero+0x4d/0x220
[  136.394025]  ? lock_release+0x410/0x410
[  136.394705]  ? lock_acquire+0x172/0x520
[  136.395386]  ? percpu_ref_switch_to_atomic_rcu+0x139/0x320
[  136.396277]  ? lock_release+0x410/0x410
[  136.396961]  _raw_spin_lock+0x30/0x40
[  136.397620]  ? io_file_data_ref_zero+0x4d/0x220
[  136.398392]  io_file_data_ref_zero+0x4d/0x220
[  136.399138]  percpu_ref_switch_to_atomic_rcu+0x310/0x320
[  136.400007]  ? percpu_ref_init+0x180/0x180
[  136.400730]  rcu_core+0x49c/0xb70
[  136.401344]  ? rcu_core+0x451/0xb70
[  136.401978]  ? strict_work_handler+0x150/0x150
[  136.402740]  ? rcu_read_lock_sched_held+0xa1/0xd0
[  136.403535]  ? rcu_read_lock_bh_held+0xb0/0xb0
[  136.404298]  rcu_core_si+0xe/0x10
[  136.404914]  __do_softirq+0x104/0x59d
[  136.405572]  asm_call_irq_on_stack+0x12/0x20
[  136.406306]  </IRQ>
[  136.406760]  do_softirq_own_stack+0x6f/0x80
[  136.407484]  irq_exit_rcu+0xf3/0x100
[  136.408134]  sysvec_apic_timer_interrupt+0x4b/0xb0
[  136.408946]  asm_sysvec_apic_timer_interrupt+0x12/0x20
[  136.409798] RIP: 0010:default_idle+0x1c/0x20
[  136.410536] Code: eb cd 66 66 2e 0f 1f 84 00 00 00 00 00 90 0f 1f 44 00 00 55 48 89 e5 e8 b2 b1 a6 fe e9 07 00 00 00 0f 00 2d 26 f1 5c 00 fb f4 <5d> c3 cc cc 0f 1f 44 00 00 55 48 89 e5 41 55 4c 8b 2d 8e c2 00 02
[  136.413291] RSP: 0018:ffffc9000011fda8 EFLAGS: 00000206
[  136.414150] RAX: 00000000000cc0ed RBX: 0000000000000005 RCX: dffffc0000000000
[  136.415256] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff8285578e
[  136.416364] RBP: ffffc9000011fda8 R08: 0000000000000001 R09: 0000000000000001
[  136.417474] R10: ffff8881e877546b R11: ffffed103d0eea8d R12: 0000000000000005
[  136.418579] R13: ffffffff84538220 R14: 0000000000000000 R15: ffff888100808000
[  136.419694]  ? default_idle+0xe/0x20
[  136.420340]  ? default_idle+0xe/0x20
[  136.420995]  arch_cpu_idle+0x15/0x20
[  136.421640]  default_idle_call+0x95/0x2c0
[  136.422343]  do_idle+0x3bd/0x480
[  136.422947]  ? arch_cpu_idle_exit+0x40/0x40
[  136.423679]  cpu_startup_entry+0x20/0x30
[  136.424369]  start_secondary+0x1c7/0x220
[  136.425067]  ? set_cpu_sibling_map+0xdc0/0xdc0
[  136.425829]  ? set_bringup_idt_handler.constprop.0+0x84/0x90
[  136.426746]  ? start_cpu0+0xc/0xc
[  136.427357]  secondary_startup_64_no_verify+0xb0/0xbb