linux-kernel - Re: [RFC patch 25/41] mm/kasan: Simplify stacktrace handling

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Message-ID: <alpine.DEB.2.21.1904141858300.4917@nanos.tec.linutronix.de>
Date:   Sun, 14 Apr 2019 19:00:37 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com,
        linux-mm@...ck.org
Subject: Re: [RFC patch 25/41] mm/kasan: Simplify stacktrace handling

On Sun, 14 Apr 2019, Thomas Gleixner wrote:
> On Wed, 10 Apr 2019, Josh Poimboeuf wrote:
> > On Wed, Apr 10, 2019 at 12:28:19PM +0200, Thomas Gleixner wrote:
> > > Replace the indirection through struct stack_trace by using the storage
> > > array based interfaces.
> > > 
> > > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> > > Cc: Andrey Ryabinin <aryabinin@...tuozzo.com>
> > > Cc: Alexander Potapenko <glider@...gle.com>
> > > Cc: Dmitry Vyukov <dvyukov@...gle.com>
> > > Cc: kasan-dev@...glegroups.com
> > > Cc: linux-mm@...ck.org
> > > ---
> > >  mm/kasan/common.c |   30 ++++++++++++------------------
> > >  mm/kasan/report.c |    7 ++++---
> > >  2 files changed, 16 insertions(+), 21 deletions(-)
> > > 
> > > --- a/mm/kasan/common.c
> > > +++ b/mm/kasan/common.c
> > > @@ -48,34 +48,28 @@ static inline int in_irqentry_text(unsig
> > >  		 ptr < (unsigned long)&__softirqentry_text_end);
> > >  }
> > >  
> > > -static inline void filter_irq_stacks(struct stack_trace *trace)
> > > +static inline unsigned int filter_irq_stacks(unsigned long *entries,
> > > +					     unsigned int nr_entries)
> > >  {
> > > -	int i;
> > > +	unsigned int i;
> > >  
> > > -	if (!trace->nr_entries)
> > > -		return;
> > > -	for (i = 0; i < trace->nr_entries; i++)
> > > -		if (in_irqentry_text(trace->entries[i])) {
> > > +	for (i = 0; i < nr_entries; i++) {
> > > +		if (in_irqentry_text(entries[i])) {
> > >  			/* Include the irqentry function into the stack. */
> > > -			trace->nr_entries = i + 1;
> > > -			break;
> > > +			return i + 1;
> > 
> > Isn't this an off-by-one error if "i" points to the last entry of the
> > array?
> 
> Yes, copied one ...

Oh, no. The point is that it returns the number of stack entries to
store. So if i == nr_entries - 1, then it returns nr_entries, i.e. all
entries are stored.

Thanks,

	tglx