[PATCH] powerpc/smp: Move rcu_cpu_starting() earlier

[PATCH] powerpc/smp: Move rcu_cpu_starting() earlier

[Qian Cai]

The call to rcu_cpu_starting() in start_secondary() is not early enough
in the CPU-hotplug onlining process, which results in lockdep splats as
follows:

 WARNING: suspicious RCU usage
 -----------------------------
 kernel/locking/lockdep.c:3497 RCU-list traversed in non-reader section!!

 other info that might help us debug this:

 RCU used illegally from offline CPU!
 rcu_scheduler_active = 1, debug_locks = 1
 no locks held by swapper/1/0.

 Call Trace:
 dump_stack+0xec/0x144 (unreliable)
 lockdep_rcu_suspicious+0x128/0x14c
 __lock_acquire+0x1060/0x1c60
 lock_acquire+0x140/0x5f0
 _raw_spin_lock_irqsave+0x64/0xb0
 clockevents_register_device+0x74/0x270
 register_decrementer_clockevent+0x94/0x110
 start_secondary+0x134/0x800
 start_secondary_prolog+0x10/0x14

This is avoided by moving the call to rcu_cpu_starting up near the
beginning of the start_secondary() function. Note that the
raw_smp_processor_id() is required in order to avoid calling into
lockdep before RCU has declared the CPU to be watched for readers.

Link: https://lore.kernel.org/lkml/160223032121.7002.1269740091547117869.tip-bot2@tip-bot2/
Signed-off-by: Qian Cai <cai@redhat.com>
---
 arch/powerpc/kernel/smp.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 3c6b9822f978..8c2857cbd960 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -1393,13 +1393,14 @@ static void add_cpu_to_masks(int cpu)
 /* Activate a secondary processor. */
 void start_secondary(void *unused)
 {
-	unsigned int cpu = smp_processor_id();
+	unsigned int cpu = raw_smp_processor_id();
 
 	mmgrab(&init_mm);
 	current->active_mm = &init_mm;
 
 	smp_store_cpu_info(cpu);
 	set_dec(tb_ticks_per_jiffy);
+	rcu_cpu_starting(cpu);
 	preempt_disable();
 	cpu_callin_map[cpu] = 1;
 
-- 
2.28.0

Re: [PATCH] powerpc/smp: Move rcu_cpu_starting() earlier

[Paul E. McKenney]

On Wed, Oct 28, 2020 at 02:23:34PM -0400, Qian Cai wrote:
> The call to rcu_cpu_starting() in start_secondary() is not early enough
> in the CPU-hotplug onlining process, which results in lockdep splats as
> follows:
> 
>  WARNING: suspicious RCU usage
>  -----------------------------
>  kernel/locking/lockdep.c:3497 RCU-list traversed in non-reader section!!
> 
>  other info that might help us debug this:
> 
>  RCU used illegally from offline CPU!
>  rcu_scheduler_active = 1, debug_locks = 1
>  no locks held by swapper/1/0.
> 
>  Call Trace:
>  dump_stack+0xec/0x144 (unreliable)
>  lockdep_rcu_suspicious+0x128/0x14c
>  __lock_acquire+0x1060/0x1c60
>  lock_acquire+0x140/0x5f0
>  _raw_spin_lock_irqsave+0x64/0xb0
>  clockevents_register_device+0x74/0x270
>  register_decrementer_clockevent+0x94/0x110
>  start_secondary+0x134/0x800
>  start_secondary_prolog+0x10/0x14
> 
> This is avoided by moving the call to rcu_cpu_starting up near the
> beginning of the start_secondary() function. Note that the
> raw_smp_processor_id() is required in order to avoid calling into
> lockdep before RCU has declared the CPU to be watched for readers.
> 
> Link: https://lore.kernel.org/lkml/160223032121.7002.1269740091547117869.tip-bot2@tip-bot2/
> Signed-off-by: Qian Cai <cai@redhat.com>

Acked-by: Paul E. McKenney <paulmck@kernel.org>

> ---
>  arch/powerpc/kernel/smp.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
> index 3c6b9822f978..8c2857cbd960 100644
> --- a/arch/powerpc/kernel/smp.c
> +++ b/arch/powerpc/kernel/smp.c
> @@ -1393,13 +1393,14 @@ static void add_cpu_to_masks(int cpu)
>  /* Activate a secondary processor. */
>  void start_secondary(void *unused)
>  {
> -	unsigned int cpu = smp_processor_id();
> +	unsigned int cpu = raw_smp_processor_id();
>  
>  	mmgrab(&init_mm);
>  	current->active_mm = &init_mm;
>  
>  	smp_store_cpu_info(cpu);
>  	set_dec(tb_ticks_per_jiffy);
> +	rcu_cpu_starting(cpu);
>  	preempt_disable();
>  	cpu_callin_map[cpu] = 1;
>  
> -- 
> 2.28.0
> 

Re: [PATCH] powerpc/smp: Move rcu_cpu_starting() earlier

[Michael Ellerman]

Qian Cai <cai@redhat.com> writes:
> The call to rcu_cpu_starting() in start_secondary() is not early enough
> in the CPU-hotplug onlining process, which results in lockdep splats as
> follows:

Since when?
What kernel version?

I haven't seen this running CPU hotplug tests with PROVE_LOCKING=y on
v5.10-rc1. Am I missing a CONFIG?

cheers


>  WARNING: suspicious RCU usage
>  -----------------------------
>  kernel/locking/lockdep.c:3497 RCU-list traversed in non-reader section!!
>
>  other info that might help us debug this:
>
>  RCU used illegally from offline CPU!
>  rcu_scheduler_active = 1, debug_locks = 1
>  no locks held by swapper/1/0.
>
>  Call Trace:
>  dump_stack+0xec/0x144 (unreliable)
>  lockdep_rcu_suspicious+0x128/0x14c
>  __lock_acquire+0x1060/0x1c60
>  lock_acquire+0x140/0x5f0
>  _raw_spin_lock_irqsave+0x64/0xb0
>  clockevents_register_device+0x74/0x270
>  register_decrementer_clockevent+0x94/0x110
>  start_secondary+0x134/0x800
>  start_secondary_prolog+0x10/0x14
>
> This is avoided by moving the call to rcu_cpu_starting up near the
> beginning of the start_secondary() function. Note that the
> raw_smp_processor_id() is required in order to avoid calling into
> lockdep before RCU has declared the CPU to be watched for readers.
>
> Link: https://lore.kernel.org/lkml/160223032121.7002.1269740091547117869.tip-bot2@tip-bot2/
> Signed-off-by: Qian Cai <cai@redhat.com>
> ---
>  arch/powerpc/kernel/smp.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
> index 3c6b9822f978..8c2857cbd960 100644
> --- a/arch/powerpc/kernel/smp.c
> +++ b/arch/powerpc/kernel/smp.c
> @@ -1393,13 +1393,14 @@ static void add_cpu_to_masks(int cpu)
>  /* Activate a secondary processor. */
>  void start_secondary(void *unused)
>  {
> -	unsigned int cpu = smp_processor_id();
> +	unsigned int cpu = raw_smp_processor_id();
>  
>  	mmgrab(&init_mm);
>  	current->active_mm = &init_mm;
>  
>  	smp_store_cpu_info(cpu);
>  	set_dec(tb_ticks_per_jiffy);
> +	rcu_cpu_starting(cpu);
>  	preempt_disable();
>  	cpu_callin_map[cpu] = 1;
>  
> -- 
> 2.28.0

Re: [PATCH] powerpc/smp: Move rcu_cpu_starting() earlier

[Paul E. McKenney]

On Thu, Oct 29, 2020 at 11:09:07AM +1100, Michael Ellerman wrote:
> Qian Cai <cai@redhat.com> writes:
> > The call to rcu_cpu_starting() in start_secondary() is not early enough
> > in the CPU-hotplug onlining process, which results in lockdep splats as
> > follows:
> 
> Since when?
> What kernel version?
> 
> I haven't seen this running CPU hotplug tests with PROVE_LOCKING=y on
> v5.10-rc1. Am I missing a CONFIG?

My guess would be that adding CONFIG_PROVE_RAW_LOCK_NESTING=y will
get you some splats.

							Thanx, Paul

> cheers
> 
> 
> >  WARNING: suspicious RCU usage
> >  -----------------------------
> >  kernel/locking/lockdep.c:3497 RCU-list traversed in non-reader section!!
> >
> >  other info that might help us debug this:
> >
> >  RCU used illegally from offline CPU!
> >  rcu_scheduler_active = 1, debug_locks = 1
> >  no locks held by swapper/1/0.
> >
> >  Call Trace:
> >  dump_stack+0xec/0x144 (unreliable)
> >  lockdep_rcu_suspicious+0x128/0x14c
> >  __lock_acquire+0x1060/0x1c60
> >  lock_acquire+0x140/0x5f0
> >  _raw_spin_lock_irqsave+0x64/0xb0
> >  clockevents_register_device+0x74/0x270
> >  register_decrementer_clockevent+0x94/0x110
> >  start_secondary+0x134/0x800
> >  start_secondary_prolog+0x10/0x14
> >
> > This is avoided by moving the call to rcu_cpu_starting up near the
> > beginning of the start_secondary() function. Note that the
> > raw_smp_processor_id() is required in order to avoid calling into
> > lockdep before RCU has declared the CPU to be watched for readers.
> >
> > Link: https://lore.kernel.org/lkml/160223032121.7002.1269740091547117869.tip-bot2@tip-bot2/
> > Signed-off-by: Qian Cai <cai@redhat.com>
> > ---
> >  arch/powerpc/kernel/smp.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
> > index 3c6b9822f978..8c2857cbd960 100644
> > --- a/arch/powerpc/kernel/smp.c
> > +++ b/arch/powerpc/kernel/smp.c
> > @@ -1393,13 +1393,14 @@ static void add_cpu_to_masks(int cpu)
> >  /* Activate a secondary processor. */
> >  void start_secondary(void *unused)
> >  {
> > -	unsigned int cpu = smp_processor_id();
> > +	unsigned int cpu = raw_smp_processor_id();
> >  
> >  	mmgrab(&init_mm);
> >  	current->active_mm = &init_mm;
> >  
> >  	smp_store_cpu_info(cpu);
> >  	set_dec(tb_ticks_per_jiffy);
> > +	rcu_cpu_starting(cpu);
> >  	preempt_disable();
> >  	cpu_callin_map[cpu] = 1;
> >  
> > -- 
> > 2.28.0

Re: [PATCH] powerpc/smp: Move rcu_cpu_starting() earlier

[Qian Cai]

On Wed, 2020-10-28 at 17:31 -0700, Paul E. McKenney wrote:
> On Thu, Oct 29, 2020 at 11:09:07AM +1100, Michael Ellerman wrote:
> > Qian Cai <cai@redhat.com> writes:
> > > The call to rcu_cpu_starting() in start_secondary() is not early enough
> > > in the CPU-hotplug onlining process, which results in lockdep splats as
> > > follows:
> > 
> > Since when?
> > What kernel version?
> > 
> > I haven't seen this running CPU hotplug tests with PROVE_LOCKING=y on
> > v5.10-rc1. Am I missing a CONFIG?
> 
> My guess would be that adding CONFIG_PROVE_RAW_LOCK_NESTING=y will
> get you some splats.

Well, I don't have that set, so it should be CONFIG_PROVE_RCU_LIST=y. Anyway,
this is .config to reproduce on Power9 NV:

https://cailca.coding.net/public/linux/mm/git/files/master/powerpc.config

Re: [PATCH] powerpc/smp: Move rcu_cpu_starting() earlier

[Qian Cai]

On Thu, 2020-10-29 at 11:09 +1100, Michael Ellerman wrote:
> Qian Cai <cai@redhat.com> writes:
> > The call to rcu_cpu_starting() in start_secondary() is not early enough
> > in the CPU-hotplug onlining process, which results in lockdep splats as
> > follows:
> 
> Since when?

For me, it is since the commit in the link which looks now merged into
v5.10-rc1. Then, it needs CONFIG_PROVE_RCU_LIST=y.

> What kernel version?
> 
> I haven't seen this running CPU hotplug tests with PROVE_LOCKING=y on
> v5.10-rc1. Am I missing a CONFIG?
> 
> cheers
> 
> 
> >  WARNING: suspicious RCU usage
> >  -----------------------------
> >  kernel/locking/lockdep.c:3497 RCU-list traversed in non-reader section!!
> > 
> >  other info that might help us debug this:
> > 
> >  RCU used illegally from offline CPU!
> >  rcu_scheduler_active = 1, debug_locks = 1
> >  no locks held by swapper/1/0.
> > 
> >  Call Trace:
> >  dump_stack+0xec/0x144 (unreliable)
> >  lockdep_rcu_suspicious+0x128/0x14c
> >  __lock_acquire+0x1060/0x1c60
> >  lock_acquire+0x140/0x5f0
> >  _raw_spin_lock_irqsave+0x64/0xb0
> >  clockevents_register_device+0x74/0x270
> >  register_decrementer_clockevent+0x94/0x110
> >  start_secondary+0x134/0x800
> >  start_secondary_prolog+0x10/0x14
> > 
> > This is avoided by moving the call to rcu_cpu_starting up near the
> > beginning of the start_secondary() function. Note that the
> > raw_smp_processor_id() is required in order to avoid calling into
> > lockdep before RCU has declared the CPU to be watched for readers.
> > 
> > Link: 
> > https://lore.kernel.org/lkml/160223032121.7002.1269740091547117869.tip-bot2@tip-bot2/
> > Signed-off-by: Qian Cai <cai@redhat.com>
> > ---
> >  arch/powerpc/kernel/smp.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
> > index 3c6b9822f978..8c2857cbd960 100644
> > --- a/arch/powerpc/kernel/smp.c
> > +++ b/arch/powerpc/kernel/smp.c
> > @@ -1393,13 +1393,14 @@ static void add_cpu_to_masks(int cpu)
> >  /* Activate a secondary processor. */
> >  void start_secondary(void *unused)
> >  {
> > -	unsigned int cpu = smp_processor_id();
> > +	unsigned int cpu = raw_smp_processor_id();
> >  
> >  	mmgrab(&init_mm);
> >  	current->active_mm = &init_mm;
> >  
> >  	smp_store_cpu_info(cpu);
> >  	set_dec(tb_ticks_per_jiffy);
> > +	rcu_cpu_starting(cpu);
> >  	preempt_disable();
> >  	cpu_callin_map[cpu] = 1;
> >  
> > -- 
> > 2.28.0

Re: [PATCH] powerpc/smp: Move rcu_cpu_starting() earlier

[Michael Ellerman]

On Wed, 28 Oct 2020 14:23:34 -0400, Qian Cai wrote:
> The call to rcu_cpu_starting() in start_secondary() is not early enough
> in the CPU-hotplug onlining process, which results in lockdep splats as
> follows:
> 
>  WARNING: suspicious RCU usage
>  -----------------------------
>  kernel/locking/lockdep.c:3497 RCU-list traversed in non-reader section!!
> 
> [...]

Applied to powerpc/fixes.

[1/1] powerpc/smp: Call rcu_cpu_starting() earlier
      https://git.kernel.org/powerpc/c/99f070b62322a4b8c1252952735806d09eb44b68

cheers