linux-kernel - Re: [PATCH v7 5/7] mm, kasan: Stackdepot implementation. Enable stackdepot for SLAB

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Message-ID: <CAG_fn=W_zM0u_NjSzJNi9KiNRY=rtQSYWTVfOQ2nGedApWMBdg@mail.gmail.com>
Date:	Mon, 11 Apr 2016 16:39:08 +0200
From:	Alexander Potapenko <glider@...gle.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	Andrey Konovalov <adech.fo@...il.com>,
	Christoph Lameter <cl@...ux.com>,
	Dmitriy Vyukov <dvyukov@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Kostya Serebryany <kcc@...gle.com>,
	kasan-dev <kasan-dev@...glegroups.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: [PATCH v7 5/7] mm, kasan: Stackdepot implementation. Enable
 stackdepot for SLAB

On Mon, Apr 11, 2016 at 9:44 AM, Joonsoo Kim <iamjoonsoo.kim@....com> wrote:
> On Mon, Mar 14, 2016 at 11:43:43AM +0100, Alexander Potapenko wrote:
>> +depot_stack_handle_t depot_save_stack(struct stack_trace *trace,
>> +                                 gfp_t alloc_flags)
>> +{
>> +     u32 hash;
>> +     depot_stack_handle_t retval = 0;
>> +     struct stack_record *found = NULL, **bucket;
>> +     unsigned long flags;
>> +     struct page *page = NULL;
>> +     void *prealloc = NULL;
>> +     bool *rec;
>> +
>> +     if (unlikely(trace->nr_entries == 0))
>> +             goto fast_exit;
>> +
>> +     rec = this_cpu_ptr(&depot_recursion);
>> +     /* Don't store the stack if we've been called recursively. */
>> +     if (unlikely(*rec))
>> +             goto fast_exit;
>> +     *rec = true;
>> +
>> +     hash = hash_stack(trace->entries, trace->nr_entries);
>> +     /* Bad luck, we won't store this stack. */
>> +     if (hash == 0)
>> +             goto exit;
>
> Hello,
>
> why is hash == 0 skipped?
>
> Thanks.
We have to keep a special value to distinguish allocations for which
we don't have the stack trace for some reason.
Making 0 such a value seems natural.


-- 
Alexander Potapenko
Software Engineer

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