linux-kernel - Re: [tip:core/rcu] lockdep: Make RCU suspicious-access splats use pr

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Date:   Tue, 31 Jan 2017 09:51:05 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     "H. Peter Anvin" <hpa@...or.com>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-tip-commits@...r.kernel.org
Subject: Re: [tip:core/rcu] lockdep: Make RCU suspicious-access splats use
 pr_err


* Dmitry Vyukov <dvyukov@...gle.com> wrote:

> On Tue, Jan 31, 2017 at 8:54 AM, tip-bot for Paul E. McKenney
> <tipbot@...or.com> wrote:
> > Commit-ID:  4d4f88fa235f7f9ef8213564dc1804144332238b
> > Gitweb:     http://git.kernel.org/tip/4d4f88fa235f7f9ef8213564dc1804144332238b
> > Author:     Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > AuthorDate: Sat, 5 Nov 2016 04:17:15 -0700
> > Committer:  Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > CommitDate: Mon, 23 Jan 2017 11:31:54 -0800
> >
> > lockdep: Make RCU suspicious-access splats use pr_err
> >
> > This commit switches RCU suspicious-access splats use pr_err()
> > instead of the current INFO printk()s.  This change makes it easier
> > to automatically classify splats.
> >
> > Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > ---
> >  kernel/locking/lockdep.c | 12 ++++++------
> >  1 file changed, 6 insertions(+), 6 deletions(-)
> >
> > diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> > index 7c38f8f..d9a698e 100644
> > --- a/kernel/locking/lockdep.c
> > +++ b/kernel/locking/lockdep.c
> > @@ -4412,13 +4412,13 @@ void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
> >  #endif /* #ifdef CONFIG_PROVE_RCU_REPEATEDLY */
> >         /* Note: the following can be executed concurrently, so be careful. */
> >         printk("\n");
> > -       printk("===============================\n");
> > -       printk("[ INFO: suspicious RCU usage. ]\n");
> > +       pr_err("===============================\n");
> > +       pr_err("[ ERR: suspicious RCU usage.  ]\n");
> 
> 
> Can we please make rcu reports look like all other kernel reports, e.g.:
> 
> WARNING: suspicious RCU usage

It was a prettification/typographical concept, as this:

  ===============================
  [ INFO: suspicious RCU usage. ]
  ===============================

looks better than this:

  ===========================
  INFO: suspicious RCU usage.
  ===========================

> I.e. prefix with a standard prefix (BUG/WARNING) and remove the [ ]
> that are used only in rcu/lockdep reports (is there any particular
> idea behind using [ ] in these reports and nowhere else?).

So lockdep was the first subsystem who started using the INFO/WARNING style of 
coherent warning messages, and it spread elsewhere from there I think, minus 
typographical details.

Arguably this would look even nicer:

  ==============================
  | INFO: suspicious RCU usage |
  ==============================

But I don't have very strong feelings about this and could live with this as well:

  ==========================
  INFO: suspicious RCU usage
  ==========================

(note the lack of the full stop.)

Thanks,

	Ingo