Subject: Re: [tip: locking/core] lockdep: Fix lockdep recursion

From: Qian Cai <[email-masked]>
Date: Wed, 28 Oct 2020 10:39:47 -0400

On Tue, 2020-10-27 at 20:01 -0700, Paul E. McKenney wrote:
> If I have the right email thread associated with the right fixes, these
> commits in -rcu should be what you are looking for:
> 
> 73b658b6b7d5 ("rcu: Prevent lockdep-RCU splats on lock acquisition/release")
> 626b79aa935a ("x86/smpboot:  Move rcu_cpu_starting() earlier")
> 
> And maybe this one as well:
> 
> 3a6f638cb95b ("rcu,ftrace: Fix ftrace recursion")
> 
> Please let me know if these commits do not fix things.
While those patches silence the warnings for x86. Other arches are still
suffering. It is only after applying the patch from Boqun below fixed
everything.

Is it a good idea for Boqun to write a formal patch or we should fix all arches
individually like "x86/smpboot: Move rcu_cpu_starting() earlier"?

> > > diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
> > > index 39334d2d2b37..35d9bab65b75 100644
> > > --- a/kernel/rcu/update.c
> > > +++ b/kernel/rcu/update.c
> > > @@ -275,8 +275,8 @@ EXPORT_SYMBOL_GPL(rcu_callback_map);
> > >  
> > >  noinstr int notrace debug_lockdep_rcu_enabled(void)
> > >  {
> > > -	return rcu_scheduler_active != RCU_SCHEDULER_INACTIVE && debug_locks &&
> > > -	       current->lockdep_recursion == 0;
> > > +	return rcu_scheduler_active != RCU_SCHEDULER_INACTIVE &&
> > > +	       __lockdep_enabled;
> > >  }
> > >  EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);

The warnings for each arch are:

== powerpc ==
[    0.176044][    T1] smp: Bringing up secondary CPUs ...
[    0.179731][    T0] 
[    0.179734][    T0] =============================
[    0.179736][    T0] WARNING: suspicious RCU usage
[    0.179739][    T0] 5.10.0-rc1-next-20201028+ #2 Not tainted
[    0.179741][    T0] -----------------------------
[    0.179744][    T0] kernel/locking/lockdep.c:3497 RCU-list traversed in non-reader section!!
[    0.179745][    T0] 
[    0.179745][    T0] other info that might help us debug this:
[    0.179745][    T0] 
[    0.179748][    T0] 
[    0.179748][    T0] RCU used illegally from offline CPU!
[    0.179748][    T0] rcu_scheduler_active = 1, debug_locks = 1
[    0.179750][    T0] no locks held by swapper/1/0.
[    0.179752][    T0] 
[    0.179752][    T0] stack backtrace:
[    0.179757][    T0] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.10.0-rc1-next-20201028+ #2
[    0.179759][    T0] Call Trace:
[    0.179767][    T0] [c000000015b27ab0] [c000000000657188] dump_stack+0xec/0x144 (unreliable)
[    0.179776][    T0] [c000000015b27af0] [c00000000014d0d4] lockdep_rcu_suspicious+0x128/0x14c
[    0.179782][    T0] [c000000015b27b70] [c000000000148920] __lock_acquire+0x1060/0x1c60
[    0.179788][    T0] [c000000015b27ca0] [c00000000014a1d0] lock_acquire+0x140/0x5f0
[    0.179794][    T0] [c000000015b27d90] [c0000000008f22f4] _raw_spin_lock_irqsave+0x64/0xb0
[    0.179801][    T0] [c000000015b27dd0] [c0000000001a1094] clockevents_register_device+0x74/0x270
[    0.179808][    T0] [c000000015b27e80] [c00000000001f194] register_decrementer_clockevent+0x94/0x110
[    0.179814][    T0] [c000000015b27ef0] [c00000000003fd84] start_secondary+0x134/0x800
[    0.179819][    T0] [c000000015b27f90] [c00000000000c454] start_secondary_prolog+0x10/0x14
[    0.179855][    T0] 
[    0.179857][    T0] =============================
[    0.179858][    T0] WARNING: suspicious RCU usage
[    0.179860][    T0] 5.10.0-rc1-next-20201028+ #2 Not tainted
[    0.179862][    T0] -----------------------------
[    0.179864][    T0] kernel/locking/lockdep.c:886 RCU-list traversed in non-reader section!!
[    0.179866][    T0] 
[    0.179866][    T0] other info that might help us debug this:
[    0.179866][    T0] 
[    0.179868][    T0] 
[    0.179868][    T0] RCU used illegally from offline CPU!
[    0.179868][    T0] rcu_scheduler_active = 1, debug_locks = 1
[    0.179870][    T0] no locks held by swapper/1/0.
[    0.179871][    T0] 
[    0.179871][    T0] stack backtrace:
[    0.179875][    T0] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.10.0-rc1-next-20201028+ #2
[    0.179876][    T0] Call Trace:
[    0.179880][    T0] [c000000015b27980] [c000000000657188] dump_stack+0xec/0x144 (unreliable)
[    0.179886][    T0] [c000000015b279c0] [c00000000014d0d4] lockdep_rcu_suspicious+0x128/0x14c
[    0.179892][    T0] [c000000015b27a40] [c00000000014b010] register_lock_class+0x680/0xc70
[    0.179896][    T0] [c000000015b27b50] [c00000000014795c] __lock_acquire+0x9c/0x1c60
[    0.179901][    T0] [c000000015b27c80] [c00000000014a1d0] lock_acquire+0x140/0x5f0
[    0.179906][    T0] [c000000015b27d70] [c0000000008f22f4] _raw_spin_lock_irqsave+0x64/0xb0
[    0.179912][    T0] [c000000015b27db0] [c0000000003a2fb4] __delete_object+0x44/0x80
[    0.179917][    T0] [c000000015b27de0] [c00000000035a964] slab_free_freelist_hook+0x174/0x300
[    0.179921][    T0] [c000000015b27e50] [c00000000035f848] kfree+0xf8/0x500
[    0.179926][    T0] [c000000015b27ed0] [c000000000656878] free_cpumask_var+0x18/0x30
[    0.179931][    T0] [c000000015b27ef0] [c00000000003fff0] start_secondary+0x3a0/0x800
add_cpu_to_masks at arch/powerpc/kernel/smp.c:1390
(inlined by) start_secondary at arch/powerpc/kernel/smp.c:1420
[    0.179936][    T0] [c000000015b27f90] [c00000000000c454] start_secondary_prolog+0x10/0x14
[    0.955418][    T1] smp: Brought up 2 nodes, 128 CPUs

== arm64 ==
[    0.473124][    T0] CPU1: Booted secondary processor 0x0000000100 [0x431f0af1]
[    0.473180][    C1] 
[    0.473183][    C1] =============================
[    0.473186][    C1] WARNING: suspicious RCU usage
[    0.473188][    C1] 5.10.0-rc1-next-20201028+ #3 Not tainted
[    0.473190][    C1] -----------------------------
[    0.473193][    C1] kernel/locking/lockdep.c:3497 RCU-list traversed in non-reader section!!
[    0.473194][    C1] 
[    0.473197][    C1] other info that might help us debug this:
[    0.473198][    C1] 
[    0.473200][    C1] 
[    0.473202][    C1] RCU used illegally from offline CPU!
[    0.473204][    C1] rcu_scheduler_active = 1, debug_locks = 1
[    0.473206][    C1] no locks held by swapper/1/0.
[    0.473208][    C1] 
[    0.473210][    C1] stack backtrace:
[    0.473212][    C1] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.10.0-rc1-next-20201028+ #3
[    0.473215][    C1] Call trace:
[    0.473217][    C1]  dump_backtrace+0x0/0x3c8
[    0.473219][    C1]  show_stack+0x14/0x60
[    0.473221][    C1]  dump_stack+0x14c/0x1c4
[    0.473223][    C1]  lockdep_rcu_suspicious+0x134/0x14c
[    0.473225][    C1]  __lock_acquire+0x1c30/0x2600
[    0.473227][    C1]  lock_acquire+0x274/0xc48
[    0.473229][    C1]  _raw_spin_lock+0xc8/0x140
[    0.473231][    C1]  vprintk_emit+0x90/0x3d0
[    0.473233][    C1]  vprintk_default+0x34/0x40
[    0.473235][    C1]  vprintk_func+0x378/0x590
[    0.473236][    C1]  printk+0xa8/0xd4
[    0.473239][    C1]  __cpuinfo_store_cpu+0x71c/0x868
[    0.473241][    C1]  cpuinfo_store_cpu+0x2c/0xc8
[    0.473243][    C1]  secondary_start_kernel+0x244/0x318
[    0.547541][    T0] Detected PIPT I-cache on CPU2
[    0.547562][    T0] GICv3: CPU2: found redistributor 200 region 0:0x0000000401100000

== s390 ==
00: [    0.603404] WARNING: suspicious RCU usage                                
00: [    0.603408] 5.10.0-rc1-next-20201027 #1 Not tainted                      
00: [    0.603409] -----------------------------                                
00: [    0.603459] kernel/locking/lockdep.c:3497 RCU-list traversed in non-reade
00: r section!!                                                                 
00: [    0.603460]                                                              
00: [    0.603460] other info that might help us debug this:                    
00: [    0.603460]                                                              
00: [    0.603462]                                                              
00: [    0.603462] RCU used illegally from offline CPU!                         
00: [    0.603462] rcu_scheduler_active = 1, debug_locks = 1                    
00: [    0.603463] no locks held by swapper/1/0.                                
00: [    0.603464]                                                              
00: [    0.603464] stack backtrace:                                             
00: [    0.603467] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.10.0-rc1-next-202
00: 01027 #1                                                                    
00: [    0.603469] Hardware name: IBM 2964 N96 400 (z/VM 6.4.0)                 
00: [    0.603471] Call Trace:                                                  
00: [    0.603484]  [<00000000d262a778>] show_stack+0x158/0x1f0                 
00: [    0.603487]  [<00000000d2635872>] dump_stack+0x1f2/0x238                 
00: [    0.603491]  [<00000000d167a550>] __lock_acquire+0x2640/0x4dd0           
00: [    0.603493]  [<00000000d167eda8>] lock_acquire+0x3a8/0xd08               
00: [    0.603498]  [<00000000d265b088>] _raw_spin_lock_irqsave+0xc0/0xf0       
00: [    0.603502]  [<00000000d17103f8>] clockevents_register_device+0xa8/0x528 
00:                                                                             
00: [    0.603516]  [<00000000d14f5246>] init_cpu_timer+0x33e/0x468             
00: [    0.603521]  [<00000000d151f44a>] smp_init_secondary+0x11a/0x328         
00: [    0.603525]  [<00000000d151f32a>] smp_start_secondary+0x82/0x88