linux-kernel - Re: [PATCH v3 3/6] mm/slub: use stackdepot to save stack trace in objects

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Date:   Wed, 6 Apr 2022 11:03:24 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Pekka Enberg <penberg@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        patches@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Oliver Glitta <glittao@...il.com>,
        Marco Elver <elver@...gle.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Imran Khan <imran.f.khan@...cle.com>
Subject: Re: [PATCH v3 3/6] mm/slub: use stackdepot to save stack trace in
 objects

On 4/5/22 23:40, David Rientjes wrote:
>> -static void set_track(struct kmem_cache *s, void *object,
>> +static void noinline set_track(struct kmem_cache *s, void *object,
>>  			enum track_item alloc, unsigned long addr)
>>  {
>>  	struct track *p = get_track(s, object, alloc);
>>  
>> -#ifdef CONFIG_STACKTRACE
>> +#ifdef CONFIG_STACKDEPOT
>> +	unsigned long entries[TRACK_ADDRS_COUNT];
>>  	unsigned int nr_entries;
>>  
>> -	metadata_access_enable();
>> -	nr_entries = stack_trace_save(kasan_reset_tag(p->addrs),
>> -				      TRACK_ADDRS_COUNT, 3);
>> -	metadata_access_disable();
>> -
>> -	if (nr_entries < TRACK_ADDRS_COUNT)
>> -		p->addrs[nr_entries] = 0;
>> +	nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 3);
>> +	p->handle = stack_depot_save(entries, nr_entries, GFP_NOWAIT);
> 
> I think this should also have __GFP_NOWARN set since this allocation could 
> easily fail and it would unnecessarily spam the kernel log unless we 
> actually care about the stack trace being printed later (and the patch 
> already indicates the allocation failed in print_track() when it matters).

Good point. But turns out __stack_depot_save() adds it for us already.

> Otherwise:
> 
> Acked-by: David Rientjes <rientjes@...gle.com>

Thanks!