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

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Message-ID: <20190410113115.GB4610@linux-x5ow.site>
Date:   Wed, 10 Apr 2019 13:31:15 +0200
From:   Johannes Thumshirn <jthumshirn@...e.de>
To:     Thomas Gleixner <tglx@...utronix.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, 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? 

Thanks,
	Johannes
-- 
Johannes Thumshirn                            SUSE Labs Filesystems
jthumshirn@...e.de                                +49 911 74053 689
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