linux-kernel - Re: [PATCH v4 2/4] mm,page_owner: Fix refcount imbalance

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Message-ID: <Zjj6KN0GhXbv3VYY@localhost.localdomain>
Date: Mon, 6 May 2024 17:41:28 +0200
From: Oscar Salvador <osalvador@...e.de>
To: Kees Cook <keescook@...omium.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Michal Hocko <mhocko@...e.com>,
	Vlastimil Babka <vbabka@...e.cz>, Marco Elver <elver@...gle.com>,
	Andrey Konovalov <andreyknvl@...il.com>,
	Alexander Potapenko <glider@...gle.com>,
	Alexandre Ghiti <alexghiti@...osinc.com>,
	syzbot+41bbfdb8d41003d12c0f@...kaller.appspotmail.com
Subject: Re: [PATCH v4 2/4] mm,page_owner: Fix refcount imbalance

On Mon, May 06, 2024 at 07:59:11AM -0700, Kees Cook wrote:
> Does this also fix this?
> https://lore.kernel.org/all/202405061514.23fedba1-oliver.sang@intel.com/

Hi Kess,

yes, it does.

> 
> This is a report of the backtrace changing, but the warning was
> pre-existing.
> 
> > [...]
> > -static void dec_stack_record_count(depot_stack_handle_t handle)
> > +static void dec_stack_record_count(depot_stack_handle_t handle,
> > +				   int nr_base_pages)
> >  {
> >  	struct stack_record *stack_record = __stack_depot_get_stack_record(handle);
> >  
> > -	if (stack_record)
> > -		refcount_dec(&stack_record->count);
> > +	if (!stack_record)
> > +		return;
> > +
> > +	if (refcount_sub_and_test(nr_base_pages, &stack_record->count))
> > +		pr_warn("%s: refcount went to 0 for %u handle\n", __func__,
> > +			handle);
> 
> This pr_warn() isn't needed: refcount will very loudly say the same
> thing. :)

Yes, but I wanted to get the handle so I can match it with the
backtrace.

Thanks


-- 
Oscar Salvador
SUSE Labs