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

[Qian Cai]

On Fri, 2020-10-09 at 07:58 +0000, tip-bot2 for Peter Zijlstra wrote:
> The following commit has been merged into the locking/core branch of tip:
> 
> Commit-ID:     4d004099a668c41522242aa146a38cc4eb59cb1e
> Gitweb:        
> https://git.kernel.org/tip/4d004099a668c41522242aa146a38cc4eb59cb1e
> Author:        Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> AuthorDate:    Fri, 02 Oct 2020 11:04:21 +02:00
> Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
> CommitterDate: Fri, 09 Oct 2020 08:53:30 +02:00
> 
> lockdep: Fix lockdep recursion
> 
> Steve reported that lockdep_assert*irq*(), when nested inside lockdep
> itself, will trigger a false-positive.
> 
> One example is the stack-trace code, as called from inside lockdep,
> triggering tracing, which in turn calls RCU, which then uses
> lockdep_assert_irqs_disabled().
> 
> Fixes: a21ee6055c30 ("lockdep: Change hardirq{s_enabled,_context} to per-cpu
> variables")
> Reported-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>

Reverting this linux-next commit fixed booting RCU-list warnings everywhere.

== x86 ==
[    8.101841][    T1] rcu: Hierarchical SRCU implementation.
[    8.110615][    T5] NMI watchdog: Enabled. Permanently consumes one hw-PMU counter.
[    8.153506][    T1] smp: Bringing up secondary CPUs ...
[    8.163075][    T1] x86: Booting SMP configuration:
[    8.167843][    T1] .... node  #0, CPUs:        #1
[    4.002695][    T0] 
[    4.002695][    T0] =============================
[    4.002695][    T0] WARNING: suspicious RCU usage
[    4.002695][    T0] 5.9.0-rc8-next-20201009 #2 Not tainted
[    4.002695][    T0] -----------------------------
[    4.002695][    T0] kernel/locking/lockdep.c:3497 RCU-list traversed in non-reader section!!
[    4.002695][    T0] 
[    4.002695][    T0] other info that might help us debug this:
[    4.002695][    T0] 
[    4.002695][    T0] 
[    4.002695][    T0] RCU used illegally from offline CPU!
[    4.002695][    T0] rcu_scheduler_active = 1, debug_locks = 1
[    4.002695][    T0] no locks held by swapper/1/0.
[    4.002695][    T0] 
[    4.002695][    T0] stack backtrace:
[    4.002695][    T0] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.9.0-rc8-next-20201009 #2
[    4.002695][    T0] Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019
[    4.002695][    T0] Call Trace:
[    4.002695][    T0]  dump_stack+0x99/0xcb
[    4.002695][    T0]  __lock_acquire.cold.76+0x2ad/0x3e0
lookup_chain_cache at kernel/locking/lockdep.c:3497
(inlined by) lookup_chain_cache_add at kernel/locking/lockdep.c:3517
(inlined by) validate_chain at kernel/locking/lockdep.c:3572
(inlined by) __lock_acquire at kernel/locking/lockdep.c:4837
[    4.002695][    T0]  ? lockdep_hardirqs_on_prepare+0x3d0/0x3d0
[    4.002695][    T0]  lock_acquire+0x1c8/0x820
lockdep_recursion_finish at kernel/locking/lockdep.c:435
(inlined by) lock_acquire at kernel/locking/lockdep.c:5444
(inlined by) lock_acquire at kernel/locking/lockdep.c:5407
[    4.002695][    T0]  ? __debug_object_init+0xb4/0xf50
[    4.002695][    T0]  ? memset+0x1f/0x40
[    4.002695][    T0]  ? rcu_read_unlock+0x40/0x40
[    4.002695][    T0]  ? mce_gather_info+0x170/0x170
[    4.002695][    T0]  ? arch_freq_get_on_cpu+0x270/0x270
[    4.002695][    T0]  ? mce_cpu_restart+0x40/0x40
[    4.002695][    T0]  _raw_spin_lock_irqsave+0x30/0x50
[    4.002695][    T0]  ? __debug_object_init+0xb4/0xf50
[    4.002695][    T0]  __debug_object_init+0xb4/0xf50
[    4.002695][    T0]  ? mce_amd_feature_init+0x80c/0xa70
[    4.002695][    T0]  ? debug_object_fixup+0x30/0x30
[    4.002695][    T0]  ? machine_check_poll+0x2d0/0x2d0
[    4.002695][    T0]  ? mce_cpu_restart+0x40/0x40
[    4.002695][    T0]  init_timer_key+0x29/0x220
[    4.002695][    T0]  identify_cpu+0xfcb/0x1980
[    4.002695][    T0]  identify_secondary_cpu+0x1d/0x190
[    4.002695][    T0]  smp_store_cpu_info+0x167/0x1f0
[    4.002695][    T0]  start_secondary+0x5b/0x290
[    4.002695][    T0]  secondary_startup_64_no_verify+0xb8/0xbb
[    8.379508][    T1]   #2
[    8.389728][    T1]   #3
[    8.399901][    T1] 

== s390 ==
00: [    1.539768] rcu: Hierarchical SRCU implementation.                       
00: [    1.561622] smp: Bringing up secondary CPUs ...                          
00: [    1.568677]                                                              
00: [    1.568681] =============================                                
00: [    1.568682] WARNING: suspicious RCU usage                                
00: [    1.568688] 5.9.0-rc8-next-20201009 #2 Not tainted                       
00: [    1.568688] -----------------------------                                
00: [    1.568691] kernel/locking/lockdep.c:3497 RCU-list traversed in non-reade
00: r section!!                                                                 
00: [    1.568692]                                                              
00: [    1.568692] other info that might help us debug this:                    
00: [    1.568692]                                                              
00: [    1.568694]                                                              
00: [    1.568694] RCU used illegally from offline CPU!                         
00: [    1.568694] rcu_scheduler_active = 1, debug_locks = 1                    
00: [    1.568697] no locks held by swapper/1/0.                                
00: [    1.568697]                                                              
00: [    1.568697] stack backtrace:                                             
00: [    1.568702] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.9.0-rc8-next-2020
00: 1009 #2                                                                     
00: [    1.568704] Hardware name: IBM 2964 N96 400 (z/VM 6.4.0)                 
00: [    1.568706] Call Trace:                                                  
00: [    1.568719]  [<000000011fb85370>] show_stack+0x158/0x1f0                 
00: [    1.568723]  [<000000011fb90402>] dump_stack+0x1f2/0x238                 
00: [    1.568730]  [<000000011ebd89d8>] __lock_acquire+0x2640/0x4dd0   
lookup_chain_cache at kernel/locking/lockdep.c:3497
(inlined by) lookup_chain_cache_add at kernel/locking/lockdep.c:3517
(inlined by) validate_chain at kernel/locking/lockdep.c:3572
(inlined by) __lock_acquire at kernel/locking/lockdep.c:4837
00: [    1.568732]  [<000000011ebdd230>] lock_acquire+0x3a8/0xd08 
lockdep_recursion_finish at kernel/locking/lockdep.c:435
(inlined by) lock_acquire at kernel/locking/lockdep.c:5444
(inlined by) lock_acquire at kernel/locking/lockdep.c:5407
00: [    1.568738]  [<000000011fbb5ca8>] _raw_spin_lock_irqsave+0xc0/0xf0
__raw_spin_lock_irqsave at include/linux/spinlock_api_smp.h:117
(inlined by) _raw_spin_lock_irqsave at kernel/locking/spinlock.c:159
00: [    1.568745]  [<000000011ec6e7e8>] clockevents_register_device+0xa8/0x528 
00:                                                                             
00: [    1.568748]  [<000000011ea55246>] init_cpu_timer+0x33e/0x468             
00: [    1.568754]  [<000000011ea7f4d2>] smp_init_secondary+0x11a/0x328         
00: [    1.568757]  [<000000011ea7f3b2>] smp_start_secondary+0x82/0x88
smp_start_secondary at arch/s390/kernel/smp.c:892
00: [    1.568759] no locks held by swapper/1/0.                                
00: [    1.569956] smp: Brought up 1 node, 2 CPUs

> ---
>  include/linux/lockdep.h  |  13 +++--
>  kernel/locking/lockdep.c |  99 ++++++++++++++++++++++----------------
>  2 files changed, 67 insertions(+), 45 deletions(-)
> 
> diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> index 6a584b3..b1227be 100644
> --- a/include/linux/lockdep.h
> +++ b/include/linux/lockdep.h
> @@ -534,6 +534,7 @@ do {								
> 	\
>  
>  DECLARE_PER_CPU(int, hardirqs_enabled);
>  DECLARE_PER_CPU(int, hardirq_context);
> +DECLARE_PER_CPU(unsigned int, lockdep_recursion);
>  
>  /*
>   * The below lockdep_assert_*() macros use raw_cpu_read() to access the above
> @@ -543,25 +544,27 @@ DECLARE_PER_CPU(int, hardirq_context);
>   * read the value from our previous CPU.
>   */
>  
> +#define __lockdep_enabled	(debug_locks &&
> !raw_cpu_read(lockdep_recursion))
> +
>  #define lockdep_assert_irqs_enabled()					
> \
>  do {									\
> -	WARN_ON_ONCE(debug_locks && !raw_cpu_read(hardirqs_enabled));	\
> +	WARN_ON_ONCE(__lockdep_enabled && !raw_cpu_read(hardirqs_enabled)); \
>  } while (0)
>  
>  #define lockdep_assert_irqs_disabled()					
> \
>  do {									\
> -	WARN_ON_ONCE(debug_locks && raw_cpu_read(hardirqs_enabled));	\
> +	WARN_ON_ONCE(__lockdep_enabled && raw_cpu_read(hardirqs_enabled)); \
>  } while (0)
>  
>  #define lockdep_assert_in_irq()						
> \
>  do {									\
> -	WARN_ON_ONCE(debug_locks && !raw_cpu_read(hardirq_context));	\
> +	WARN_ON_ONCE(__lockdep_enabled && !raw_cpu_read(hardirq_context)); \
>  } while (0)
>  
>  #define lockdep_assert_preemption_enabled()				\
>  do {									\
>  	WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_COUNT)	&&		\
> -		     debug_locks			&&		\
> +		     __lockdep_enabled			&&		\
>  		     (preempt_count() != 0		||		\
>  		      !raw_cpu_read(hardirqs_enabled)));		\
>  } while (0)
> @@ -569,7 +572,7 @@ do {								
> 	\
>  #define lockdep_assert_preemption_disabled()				\
>  do {									\
>  	WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_COUNT)	&&		\
> -		     debug_locks			&&		\
> +		     __lockdep_enabled			&&		\
>  		     (preempt_count() == 0		&&		\
>  		      raw_cpu_read(hardirqs_enabled)));			\
>  } while (0)
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index a430fbb..85d15f0 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -76,6 +76,23 @@ module_param(lock_stat, int, 0644);
>  #define lock_stat 0
>  #endif
>  
> +DEFINE_PER_CPU(unsigned int, lockdep_recursion);
> +EXPORT_PER_CPU_SYMBOL_GPL(lockdep_recursion);
> +
> +static inline bool lockdep_enabled(void)
> +{
> +	if (!debug_locks)
> +		return false;
> +
> +	if (raw_cpu_read(lockdep_recursion))
> +		return false;
> +
> +	if (current->lockdep_recursion)
> +		return false;
> +
> +	return true;
> +}
> +
>  /*
>   * lockdep_lock: protects the lockdep graph, the hashes and the
>   *               class/list/hash allocators.
> @@ -93,7 +110,7 @@ static inline void lockdep_lock(void)
>  
>  	arch_spin_lock(&__lock);
>  	__owner = current;
> -	current->lockdep_recursion++;
> +	__this_cpu_inc(lockdep_recursion);
>  }
>  
>  static inline void lockdep_unlock(void)
> @@ -101,7 +118,7 @@ static inline void lockdep_unlock(void)
>  	if (debug_locks && DEBUG_LOCKS_WARN_ON(__owner != current))
>  		return;
>  
> -	current->lockdep_recursion--;
> +	__this_cpu_dec(lockdep_recursion);
>  	__owner = NULL;
>  	arch_spin_unlock(&__lock);
>  }
> @@ -393,10 +410,15 @@ void lockdep_init_task(struct task_struct *task)
>  	task->lockdep_recursion = 0;
>  }
>  
> +static __always_inline void lockdep_recursion_inc(void)
> +{
> +	__this_cpu_inc(lockdep_recursion);
> +}
> +
>  static __always_inline void lockdep_recursion_finish(void)
>  {
> -	if (WARN_ON_ONCE((--current->lockdep_recursion) &
> LOCKDEP_RECURSION_MASK))
> -		current->lockdep_recursion = 0;
> +	if (WARN_ON_ONCE(__this_cpu_dec_return(lockdep_recursion)))
> +		__this_cpu_write(lockdep_recursion, 0);
>  }
>  
>  void lockdep_set_selftest_task(struct task_struct *task)
> @@ -3659,7 +3681,7 @@ void lockdep_hardirqs_on_prepare(unsigned long ip)
>  	if (unlikely(in_nmi()))
>  		return;
>  
> -	if (unlikely(current->lockdep_recursion & LOCKDEP_RECURSION_MASK))
> +	if (unlikely(__this_cpu_read(lockdep_recursion)))
>  		return;
>  
>  	if (unlikely(lockdep_hardirqs_enabled())) {
> @@ -3695,7 +3717,7 @@ void lockdep_hardirqs_on_prepare(unsigned long ip)
>  
>  	current->hardirq_chain_key = current->curr_chain_key;
>  
> -	current->lockdep_recursion++;
> +	lockdep_recursion_inc();
>  	__trace_hardirqs_on_caller();
>  	lockdep_recursion_finish();
>  }
> @@ -3728,7 +3750,7 @@ void noinstr lockdep_hardirqs_on(unsigned long ip)
>  		goto skip_checks;
>  	}
>  
> -	if (unlikely(current->lockdep_recursion & LOCKDEP_RECURSION_MASK))
> +	if (unlikely(__this_cpu_read(lockdep_recursion)))
>  		return;
>  
>  	if (lockdep_hardirqs_enabled()) {
> @@ -3781,7 +3803,7 @@ void noinstr lockdep_hardirqs_off(unsigned long ip)
>  	if (in_nmi()) {
>  		if (!IS_ENABLED(CONFIG_TRACE_IRQFLAGS_NMI))
>  			return;
> -	} else if (current->lockdep_recursion & LOCKDEP_RECURSION_MASK)
> +	} else if (__this_cpu_read(lockdep_recursion))
>  		return;
>  
>  	/*
> @@ -3814,7 +3836,7 @@ void lockdep_softirqs_on(unsigned long ip)
>  {
>  	struct irqtrace_events *trace = &current->irqtrace;
>  
> -	if (unlikely(!debug_locks || current->lockdep_recursion))
> +	if (unlikely(!lockdep_enabled()))
>  		return;
>  
>  	/*
> @@ -3829,7 +3851,7 @@ void lockdep_softirqs_on(unsigned long ip)
>  		return;
>  	}
>  
> -	current->lockdep_recursion++;
> +	lockdep_recursion_inc();
>  	/*
>  	 * We'll do an OFF -> ON transition:
>  	 */
> @@ -3852,7 +3874,7 @@ void lockdep_softirqs_on(unsigned long ip)
>   */
>  void lockdep_softirqs_off(unsigned long ip)
>  {
> -	if (unlikely(!debug_locks || current->lockdep_recursion))
> +	if (unlikely(!lockdep_enabled()))
>  		return;
>  
>  	/*
> @@ -4233,11 +4255,11 @@ void lockdep_init_map_waits(struct lockdep_map *lock,
> const char *name,
>  	if (subclass) {
>  		unsigned long flags;
>  
> -		if (DEBUG_LOCKS_WARN_ON(current->lockdep_recursion))
> +		if (DEBUG_LOCKS_WARN_ON(!lockdep_enabled()))
>  			return;
>  
>  		raw_local_irq_save(flags);
> -		current->lockdep_recursion++;
> +		lockdep_recursion_inc();
>  		register_lock_class(lock, subclass, 1);
>  		lockdep_recursion_finish();
>  		raw_local_irq_restore(flags);
> @@ -4920,11 +4942,11 @@ void lock_set_class(struct lockdep_map *lock, const
> char *name,
>  {
>  	unsigned long flags;
>  
> -	if (unlikely(current->lockdep_recursion))
> +	if (unlikely(!lockdep_enabled()))
>  		return;
>  
>  	raw_local_irq_save(flags);
> -	current->lockdep_recursion++;
> +	lockdep_recursion_inc();
>  	check_flags(flags);
>  	if (__lock_set_class(lock, name, key, subclass, ip))
>  		check_chain_key(current);
> @@ -4937,11 +4959,11 @@ void lock_downgrade(struct lockdep_map *lock, unsigned
> long ip)
>  {
>  	unsigned long flags;
>  
> -	if (unlikely(current->lockdep_recursion))
> +	if (unlikely(!lockdep_enabled()))
>  		return;
>  
>  	raw_local_irq_save(flags);
> -	current->lockdep_recursion++;
> +	lockdep_recursion_inc();
>  	check_flags(flags);
>  	if (__lock_downgrade(lock, ip))
>  		check_chain_key(current);
> @@ -4979,7 +5001,7 @@ static void verify_lock_unused(struct lockdep_map *lock,
> struct held_lock *hlock
>  
>  static bool lockdep_nmi(void)
>  {
> -	if (current->lockdep_recursion & LOCKDEP_RECURSION_MASK)
> +	if (raw_cpu_read(lockdep_recursion))
>  		return false;
>  
>  	if (!in_nmi())
> @@ -5000,7 +5022,10 @@ void lock_acquire(struct lockdep_map *lock, unsigned
> int subclass,
>  
>  	trace_lock_acquire(lock, subclass, trylock, read, check, nest_lock, ip);
>  
> -	if (unlikely(current->lockdep_recursion)) {
> +	if (!debug_locks)
> +		return;
> +
> +	if (unlikely(!lockdep_enabled())) {
>  		/* XXX allow trylock from NMI ?!? */
>  		if (lockdep_nmi() && !trylock) {
>  			struct held_lock hlock;
> @@ -5023,7 +5048,7 @@ void lock_acquire(struct lockdep_map *lock, unsigned int
> subclass,
>  	raw_local_irq_save(flags);
>  	check_flags(flags);
>  
> -	current->lockdep_recursion++;
> +	lockdep_recursion_inc();
>  	__lock_acquire(lock, subclass, trylock, read, check,
>  		       irqs_disabled_flags(flags), nest_lock, ip, 0, 0);
>  	lockdep_recursion_finish();
> @@ -5037,13 +5062,13 @@ void lock_release(struct lockdep_map *lock, unsigned
> long ip)
>  
>  	trace_lock_release(lock, ip);
>  
> -	if (unlikely(current->lockdep_recursion))
> +	if (unlikely(!lockdep_enabled()))
>  		return;
>  
>  	raw_local_irq_save(flags);
>  	check_flags(flags);
>  
> -	current->lockdep_recursion++;
> +	lockdep_recursion_inc();
>  	if (__lock_release(lock, ip))
>  		check_chain_key(current);
>  	lockdep_recursion_finish();
> @@ -5056,13 +5081,13 @@ noinstr int lock_is_held_type(const struct lockdep_map
> *lock, int read)
>  	unsigned long flags;
>  	int ret = 0;
>  
> -	if (unlikely(current->lockdep_recursion))
> +	if (unlikely(!lockdep_enabled()))
>  		return 1; /* avoid false negative lockdep_assert_held() */
>  
>  	raw_local_irq_save(flags);
>  	check_flags(flags);
>  
> -	current->lockdep_recursion++;
> +	lockdep_recursion_inc();
>  	ret = __lock_is_held(lock, read);
>  	lockdep_recursion_finish();
>  	raw_local_irq_restore(flags);
> @@ -5077,13 +5102,13 @@ struct pin_cookie lock_pin_lock(struct lockdep_map
> *lock)
>  	struct pin_cookie cookie = NIL_COOKIE;
>  	unsigned long flags;
>  
> -	if (unlikely(current->lockdep_recursion))
> +	if (unlikely(!lockdep_enabled()))
>  		return cookie;
>  
>  	raw_local_irq_save(flags);
>  	check_flags(flags);
>  
> -	current->lockdep_recursion++;
> +	lockdep_recursion_inc();
>  	cookie = __lock_pin_lock(lock);
>  	lockdep_recursion_finish();
>  	raw_local_irq_restore(flags);
> @@ -5096,13 +5121,13 @@ void lock_repin_lock(struct lockdep_map *lock, struct
> pin_cookie cookie)
>  {
>  	unsigned long flags;
>  
> -	if (unlikely(current->lockdep_recursion))
> +	if (unlikely(!lockdep_enabled()))
>  		return;
>  
>  	raw_local_irq_save(flags);
>  	check_flags(flags);
>  
> -	current->lockdep_recursion++;
> +	lockdep_recursion_inc();
>  	__lock_repin_lock(lock, cookie);
>  	lockdep_recursion_finish();
>  	raw_local_irq_restore(flags);
> @@ -5113,13 +5138,13 @@ void lock_unpin_lock(struct lockdep_map *lock, struct
> pin_cookie cookie)
>  {
>  	unsigned long flags;
>  
> -	if (unlikely(current->lockdep_recursion))
> +	if (unlikely(!lockdep_enabled()))
>  		return;
>  
>  	raw_local_irq_save(flags);
>  	check_flags(flags);
>  
> -	current->lockdep_recursion++;
> +	lockdep_recursion_inc();
>  	__lock_unpin_lock(lock, cookie);
>  	lockdep_recursion_finish();
>  	raw_local_irq_restore(flags);
> @@ -5249,15 +5274,12 @@ void lock_contended(struct lockdep_map *lock, unsigned
> long ip)
>  
>  	trace_lock_acquired(lock, ip);
>  
> -	if (unlikely(!lock_stat || !debug_locks))
> -		return;
> -
> -	if (unlikely(current->lockdep_recursion))
> +	if (unlikely(!lock_stat || !lockdep_enabled()))
>  		return;
>  
>  	raw_local_irq_save(flags);
>  	check_flags(flags);
> -	current->lockdep_recursion++;
> +	lockdep_recursion_inc();
>  	__lock_contended(lock, ip);
>  	lockdep_recursion_finish();
>  	raw_local_irq_restore(flags);
> @@ -5270,15 +5292,12 @@ void lock_acquired(struct lockdep_map *lock, unsigned
> long ip)
>  
>  	trace_lock_contended(lock, ip);
>  
> -	if (unlikely(!lock_stat || !debug_locks))
> -		return;
> -
> -	if (unlikely(current->lockdep_recursion))
> +	if (unlikely(!lock_stat || !lockdep_enabled()))
>  		return;
>  
>  	raw_local_irq_save(flags);
>  	check_flags(flags);
> -	current->lockdep_recursion++;
> +	lockdep_recursion_inc();
>  	__lock_acquired(lock, ip);
>  	lockdep_recursion_finish();
>  	raw_local_irq_restore(flags);