linux-kernel - Re: [PATCH 1/2] lockdep: Introduce CROSSRELEASE_STACK

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Date:   Wed, 18 Oct 2017 15:30:19 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Byungchul Park <byungchul.park@....com>, peterz@...radead.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        kernel-team@....com
Subject: Re: [PATCH 1/2] lockdep: Introduce CROSSRELEASE_STACK_TRACE and make
 it not unwind as default


* Thomas Gleixner <tglx@...utronix.de> wrote:

> On Wed, 18 Oct 2017, Byungchul Park wrote:
> >  #ifdef CONFIG_LOCKDEP_CROSSRELEASE
> > +#ifdef CONFIG_CROSSRELEASE_STACK_TRACE
> >  #define MAX_XHLOCK_TRACE_ENTRIES 5
> > +#else
> > +#define MAX_XHLOCK_TRACE_ENTRIES 1
> > +#endif
> >  
> >  /*
> >   * This is for keeping locks waiting for commit so that true dependencies
> > diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> > index e36e652..5c2ddf2 100644
> > --- a/kernel/locking/lockdep.c
> > +++ b/kernel/locking/lockdep.c
> > @@ -4863,8 +4863,13 @@ static void add_xhlock(struct held_lock *hlock)
> >  	xhlock->trace.nr_entries = 0;
> >  	xhlock->trace.max_entries = MAX_XHLOCK_TRACE_ENTRIES;
> >  	xhlock->trace.entries = xhlock->trace_entries;
> > +#ifdef CONFIG_CROSSRELEASE_STACK_TRACE
> >  	xhlock->trace.skip = 3;
> >  	save_stack_trace(&xhlock->trace);
> > +#else
> > +	xhlock->trace.nr_entries = 1;
> > +	xhlock->trace.entries[0] = hlock->acquire_ip;
> > +#endif
> 
> Hmm. Would it be possible to have this switchable at boot time via a
> command line parameter? So in case of a splat with no stack trace, one
> could just reboot and set something like 'lockdep_fullstack' on the kernel
> command line to get the full data without having to recompile the kernel.

Yeah, and I'd suggest keeping the Kconfig option to default-enable that boot 
option as well - i.e. let's have both.

Thanks,

	Ingo