2018-05-15 22:48:10

by Joel Fernandes

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

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

2018-05-15 23:20:14

by Joel Fernandes

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

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
>