linux-kernel - Re: [RFC patch 29/41] btrfs: ref-verify: Simplify stack trace retrieval

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Message-ID: <alpine.DEB.2.21.1904101404280.3479@nanos.tec.linutronix.de>
Date:   Wed, 10 Apr 2019 14:05:17 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Johannes Thumshirn <jthumshirn@...e.de>
cc:     LKML <linux-kernel@...r.kernel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Alexander Potapenko <glider@...gle.com>,
        David Sterba <dsterba@...e.com>, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>, linux-btrfs@...r.kernel.org
Subject: Re: [RFC patch 29/41] btrfs: ref-verify: Simplify stack trace
 retrieval

On Wed, 10 Apr 2019, Johannes Thumshirn wrote:

> On Wed, Apr 10, 2019 at 12:28:23PM +0200, Thomas Gleixner wrote:
> > Replace the indirection through struct stack_trace with an invocation of
> > the storage array based interface.
> > 
> > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> > Cc: David Sterba <dsterba@...e.com>
> > Cc: Chris Mason <clm@...com>
> > Cc: Josef Bacik <josef@...icpanda.com>
> > Cc: linux-btrfs@...r.kernel.org
> > ---
> >  fs/btrfs/ref-verify.c |   15 ++-------------
> >  1 file changed, 2 insertions(+), 13 deletions(-)
> > 
> > --- a/fs/btrfs/ref-verify.c
> > +++ b/fs/btrfs/ref-verify.c
> > @@ -205,28 +205,17 @@ static struct root_entry *lookup_root_en
> >  #ifdef CONFIG_STACKTRACE
> >  static void __save_stack_trace(struct ref_action *ra)
> >  {
> > -	struct stack_trace stack_trace;
> > -
> > -	stack_trace.max_entries = MAX_TRACE;
> > -	stack_trace.nr_entries = 0;
> > -	stack_trace.entries = ra->trace;
> > -	stack_trace.skip = 2;
> > -	save_stack_trace(&stack_trace);
> > -	ra->trace_len = stack_trace.nr_entries;
> > +	ra->trace_len = stack_trace_save(ra->trace, MAX_TRACE, 2);
> 
> 
> Stupid question: why are you passing a '2' for 'skipnr' and in
> stack_trace_save() from your series you set stack_trace::skip as skipnr + 1. 
> 
> Wouldn't this result in a stack_trace::skip = 3? Or is it the number of
> functions to be skipped and you don't want to have stack_trace_save() saved as
> well? 

Correct. The extra call will shift the skipped one up, so I compensate for that.

Thanks,

	tglx