Re: [PATCH v7 1/6] softirq: reorder trace_softirqs_on to prevent lockdep splat

[Joel Fernandes]

This patch submission got completely screwed up, sorry, please ignore. I'll
repost soon. There's something messed up with my SMTP server too.

On Tue, May 15, 2018 at 03:45:54PM -0700, Joel Fernandes (Google) wrote:
> I'm able to reproduce a lockdep splat with config options:
> CONFIG_PROVE_LOCKING=y,
> CONFIG_DEBUG_LOCK_ALLOC=y and
> CONFIG_PREEMPTIRQ_EVENTS=y
> 
> $ echo 1 > /d/tracing/events/preemptirq/preempt_enable/enable
> ---
>  kernel/softirq.c | 6 +-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/softirq.c b/kernel/softirq.c
> index 177de3640c78..8a040bcaa033 100644
> --- a/kernel/softirq.c
> +++ b/kernel/softirq.c
> @@ -139,9 +139,13 @@ static void __local_bh_enable(unsigned int cnt)
>  {
>   lockdep_assert_irqs_disabled();
>  
> + if (preempt_count() == cnt)
> + trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
> +
>   if (softirq_count() == (cnt & SOFTIRQ_MASK))
>   trace_softirqs_on(_RET_IP_);
> - preempt_count_sub(cnt);
> +
> + __preempt_count_sub(cnt);
>  }
>  
>  /*
> -- 
> 2.17.0.441.gb46fe60e1d-goog
> 

Re: [PATCH v7 1/6] softirq: reorder trace_softirqs_on to prevent lockdep splat

[Joel Fernandes]

This patch submission got completely screwed up, sorry, please ignore. I'll
repost soon. There's something messed up with my SMTP server too.

On Tue, May 15, 2018 at 03:45:54PM -0700, Joel Fernandes (Google) wrote:
> I'm able to reproduce a lockdep splat with config options:
> CONFIG_PROVE_LOCKING=y,
> CONFIG_DEBUG_LOCK_ALLOC=y and
> CONFIG_PREEMPTIRQ_EVENTS=y
> 
> $ echo 1 > /d/tracing/events/preemptirq/preempt_enable/enable
> ---
>  kernel/softirq.c | 6 +-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/softirq.c b/kernel/softirq.c
> index 177de3640c78..8a040bcaa033 100644
> --- a/kernel/softirq.c
> +++ b/kernel/softirq.c
> @@ -139,9 +139,13 @@ static void __local_bh_enable(unsigned int cnt)
>  {
>   lockdep_assert_irqs_disabled();
>  
> + if (preempt_count() == cnt)
> + trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
> +
>   if (softirq_count() == (cnt & SOFTIRQ_MASK))
>   trace_softirqs_on(_RET_IP_);
> - preempt_count_sub(cnt);
> +
> + __preempt_count_sub(cnt);
>  }
>  
>  /*
> -- 
> 2.17.0.441.gb46fe60e1d-goog
> 

[PATCH v7 1/6] softirq: reorder trace_softirqs_on to prevent lockdep splat

[Joel Fernandes (Google)]

I'm able to reproduce a lockdep splat with config options:
CONFIG_PROVE_LOCKING=y,
CONFIG_DEBUG_LOCK_ALLOC=y and
CONFIG_PREEMPTIRQ_EVENTS=y

$ echo 1 > /d/tracing/events/preemptirq/preempt_enable/enable
---
 kernel/softirq.c | 6 +-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/softirq.c b/kernel/softirq.c
index 177de3640c78..8a040bcaa033 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -139,9 +139,13 @@ static void __local_bh_enable(unsigned int cnt)
 {
lockdep_assert_irqs_disabled();
 
+   if (preempt_count() == cnt)
+   trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
+
if (softirq_count() == (cnt & SOFTIRQ_MASK))
trace_softirqs_on(_RET_IP_);
-   preempt_count_sub(cnt);
+
+   __preempt_count_sub(cnt);
 }
 
 /*
-- 
2.17.0.441.gb46fe60e1d-goog

[PATCH v7 1/6] softirq: reorder trace_softirqs_on to prevent lockdep splat

[Joel Fernandes (Google)]

I'm able to reproduce a lockdep splat with config options:
CONFIG_PROVE_LOCKING=y,
CONFIG_DEBUG_LOCK_ALLOC=y and
CONFIG_PREEMPTIRQ_EVENTS=y

$ echo 1 > /d/tracing/events/preemptirq/preempt_enable/enable
---
 kernel/softirq.c | 6 +-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/softirq.c b/kernel/softirq.c
index 177de3640c78..8a040bcaa033 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -139,9 +139,13 @@ static void __local_bh_enable(unsigned int cnt)
 {
lockdep_assert_irqs_disabled();
 
+   if (preempt_count() == cnt)
+   trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
+
if (softirq_count() == (cnt & SOFTIRQ_MASK))
trace_softirqs_on(_RET_IP_);
-   preempt_count_sub(cnt);
+
+   __preempt_count_sub(cnt);
 }
 
 /*
-- 
2.17.0.441.gb46fe60e1d-goog