linux-kernel - Re: [PATCH] lockdep: Show up to three levels for a deadlock scenario

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Date:   Tue, 19 Dec 2017 18:29:37 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Dhaval Giani <dhaval.giani@...cle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] lockdep: Show up to three levels for a deadlock scenario

On Tue, Dec 19, 2017 at 12:11:24PM -0500, Steven Rostedt wrote:
> On Tue, 19 Dec 2017 18:07:16 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Tue, Dec 19, 2017 at 11:52:38AM -0500, Steven Rostedt wrote:
> > > Then I suggest that you can either take my patch to improve the
> > > visual or remove the visual completely, as nobody cares about it.  
> > 
> > Doesn't apply as is; but can you at least make it shut up if the chain
> > is longer than you support?
> 
> I can add that.
> 
> > 
> > It's really annoying if it shows the AB-BA graphics when you're staring
> > at a 5-6 lock scenario.
> 
> I could also make it dynamic, to handle the entire chain. But it will
> make it longer.

Makes it too wide I think, people already have a problem quoting the
thing in emails (wrap mangles like stupid).

Take the below while you're poking at it.. that should hopefully make
the #0 stacktrace go away.

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 5fa1324a4f29..6aa431c4ad99 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1085,7 +1085,8 @@ print_circular_bug_entry(struct lock_list *target, int depth)
 	printk("\n-> #%u", depth);
 	print_lock_name(target->class);
 	printk(KERN_CONT ":\n");
-	print_stack_trace(&target->trace, 6);
+	if (depth)
+		print_stack_trace(&target->trace, 6);
 
 	return 0;
 }