linux-kernel - Re: [PATCH v0] softirq: Call trace_preempt_on manually to prevent lockdep splatter

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Date:	Tue, 2 Jun 2015 21:37:58 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Daniel Wagner <daniel.wagner@...-carit.de>
cc:	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v0] softirq: Call trace_preempt_on manually to prevent
 lockdep splatter

On Thu, 28 May 2015, Daniel Wagner wrote:

> __do_softirq() uses __local_bh_disable_ip(SOFTIRQ_OFFSET) to disable
> SOFTIRQs and signaling that softirqs are served.
> 
> When done, __do_softirq() calls __local_bh_enable(SOFTIRQ_OFFSET)
> to enable them again. The reason it does not call
> __local_bh_enable_ip(SOFTIRQ_OFFSET) is because __local_bh_enable_ip()
> would process still-pending softirqs.
> 
> Now, we face the same problem as in __local_bh_disable_ip()
> with the preempt tracer hooking into preempt_count_sub(). This
> will case lockdep warning, when for example the kernel is configured
> to run all IRQs as threads and preemptoff tracer is activated:

.... 

> Signed-off-by: Daniel Wagner <daniel.wagner@...-carit.de>

Acked-by: Thomas Gleixner <tglx@...utronix.de>
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