linux-kernel - Re: [PATCH] locking/lockdep: Correct calling tracepoints

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Date:   Wed, 12 May 2021 16:05:33 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Leo Yan <leo.yan@...aro.org>, Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] locking/lockdep: Correct calling tracepoints

On Wed, May 12, 2021 at 09:32:02AM -0400, Steven Rostedt wrote:
> On Wed, 12 May 2021 14:37:12 +0200
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Wed, May 12, 2021 at 08:09:37PM +0800, Leo Yan wrote:
> > > The commit eb1f00237aca ("lockdep,trace: Expose tracepoints") reverses
> > > tracepoints for lock_contended() and lock_acquired(), thus the ftrace
> > > log shows the wrong locking sequence that "acquired" event is prior to
> > > "contended" event:
> > > 
> > >   <idle>-0       [001] d.s3 20803.501685: lock_acquire: 0000000008b91ab4 &sg_policy->update_lock
> > >   <idle>-0       [001] d.s3 20803.501686: lock_acquired: 0000000008b91ab4 &sg_policy->update_lock
> > >   <idle>-0       [001] d.s3 20803.501689: lock_contended: 0000000008b91ab4 &sg_policy->update_lock
> > >   <idle>-0       [001] d.s3 20803.501690: lock_release: 0000000008b91ab4 &sg_policy->update_lock
> > > 
> > > This patch fixes calling tracepoints for lock_contended() and
> > > lock_acquired().
> > > 
> > > Fixes: eb1f00237aca ("lockdep,trace: Expose tracepoints")
> > > Signed-off-by: Leo Yan <leo.yan@...aro.org>  
> > 
> > No idea how that happened, curious. Thanks for fixing though!
> 
>     Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
>     Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
>     Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
>     Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>     Tested-by: Marco Elver <elver@...gle.com>
> 
> That's embarrassing :-p

Thing is, if you look at the list copy:

  https://lore.kernel.org/lkml/20200821085348.782688941@infradead.org/

things were okay. I suspect there was a conflict at some point and
resolution got it backwards because the hunks are so similar and I never
noticed :/