linux-kernel - Re: lockdep warning: threadirqs and preemptoff tracer

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Message-ID: <55646C50.7070106@bmw-carit.de>
Date:	Tue, 26 May 2015 14:51:28 +0200
From:	Daniel Wagner <daniel.wagner@...-carit.de>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: lockdep warning: threadirqs and preemptoff tracer

On 05/26/2015 02:32 PM, Steven Rostedt wrote:
> Daniel Wagner <daniel.wagner@...-carit.de> wrote:
>> On 05/20/2015 10:46 AM, Daniel Wagner wrote:
>> I starred for a while at the code and saw the comment in
>> __local_bh_disable_ip():
>>
>> 	/*
>> 	 * The preempt tracer hooks into preempt_count_add and will break
>> 	 * lockdep because it calls back into lockdep after SOFTIRQ_OFFSET
>> 	 * is set and before current->softirq_enabled is cleared.
>> 	 * We must manually increment preempt_count here and manually
>> 	 * call the trace_preempt_off later.
>> 	 */
>>
>> >From this I figured this might be the same problem just in the
>> enable path. The below patch made the lockdep warning disappear.
>> Though I am not sure what I breaking with this.
> 
> Don't you want to modify __local_bh_enable_ip()?

__do_softirq() calls __local_bh_disable_ip() and __local_bh_enable() and
not __local_bh_enable_ip(). I have no clue why this is done this way.
Need to look into the history.
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