[alsa-devel] [PATCH] ASoC: topology: Fix not to keep a reference to tplg fw

[Takashi Iwai]

On Fri, 27 Nov 2015 10:15:19 +0100,
Subhransu S. Prusty wrote:
> 
> On Thu, Nov 26, 2015 at 06:39:02PM +0100, Takashi Iwai wrote:
> > On Thu, 26 Nov 2015 17:13:43 +0100,
> > Vinod Koul wrote:
> > > 
> > > On Thu, Nov 26, 2015 at 12:46:24PM +0100, Takashi Iwai wrote:
> > > 
> > > > > Sorry it a oops, paging request failure and not a panic
> > > > > 
> > > > > > > Your second point is applicable here as card instantiation is delayed often
> > > > > > > for us as all components may not be present and delayed probe finally
> > > > > > > creates the card.
> > > > > > > 
> > > > > > > > > Issue is caught with id#87b5ed8ecb9fe05a696e1c0b53c7a49ea66432c1
> > > > > > > > 
> > > > > > > > You should put the commit subject, too.
> > > > > > > 
> > > > > > > Yes we will add that
> > > > > > > 
> > > > > > > > > So create a copy of the memory and assign to names instead.
> > > > > > > > 
> > > > > > > > And who releases these duplicated memory?  It looks like another
> > > > > > > > memory leak to me.
> > > > > > > 
> > > > > > > That is a good point and I think we should do devm_kstrdup() here so that
> > > > > > > this is freed when we cleanup the device, or do you have any better
> > > > > > > suggestion ?
> > > > > > 
> > > > > > devm_kstrdup() is bad in this case.  You can reload the topology
> > > > > > unlimitedly, and the memory won't be freed until the device unbind,
> > > > > > thus it keeps hogging.
> > > > > > 
> > > > > > You really need to identify which path hits the issue exactly how.  In
> > > > > > general, the string passed to template is only for creating the kctl.
> > > > > > Once when kctl is created, the whole snd_kcontrol_new template and the
> > > > > > allocated string is no use, so they can be freed.
> > > > > 
> > > > > but then question of where should these be freed. For current drivers they
> > > > > declare controls statically, so memory is always there.. How do free up in
> > > > > the cases where we allocate dynamically?
> > > > 
> > > > Well, for judging this, we have to follow the code more closely.  And
> > > > it's why I asked which path does it happen exactly.
> > > > 
> > > > There are two different paths where the snd_kcontrol_new is used: the
> > > > standard controls and dapm.  The former is immediately instantiated
> > > > via snd_soc_cnew(), so it's fine as is, no need to change.  But the
> > > > latter is different.
> > > > 
> > > > The latter, dapm case, always allocates the snd_kcontrol_new array in
> > > > kcontrol_news field.  So, we need to change in each function
> > > > allocating this to do kstrdump() for each kcontrol_new element, and
> > > > each place calling kfree() of kcontrol_news should free the string of
> > > > each item in return.
> > > 
> > > It is the latter dapm case with added complexity of topology core creating
> > > these kcontrols. I will reproduce this and send the oops tomorrow
> > 
> > Not too complex in this case because there are only a few users.
> > A totally untested patch is below.
> > 
> > 
> > Takashi
> > 
> > ---
> > diff --git a/sound/soc/soc-topology.c b/sound/soc/soc-topology.c
> > index 8d7ec80af51b..1f684975b541 100644
> > --- a/sound/soc/soc-topology.c
> > +++ b/sound/soc/soc-topology.c
> > @@ -427,6 +427,16 @@ static void remove_enum(struct snd_soc_component *comp,
> >  	kfree(se);
> >  }
> >  
> > +static void free_kcontrol_news(const struct snd_kcontrol_new *_wc, int nums)
> > +{
> > +	struct snd_kcontrol_new *wc = (struct snd_kcontrol_new *)_wc;
> > +	int i;
> > +
> > +	for (i = 0; i < nums && wc[i].name; i++)
> > +		kfree(wc[i].name);
> > +	kfree(wc);
> > +}
> > +
> >  /* remove a byte kcontrol */
> >  static void remove_bytes(struct snd_soc_component *comp,
> >  	struct snd_soc_dobj *dobj, int pass)
> > @@ -477,7 +487,7 @@ static void remove_widget(struct snd_soc_component *comp,
> >  			kfree(se->dobj.control.dtexts[i]);
> >  
> >  		kfree(se);
> > -		kfree(w->kcontrol_news);
> > +		free_kcontrol_news(w->kcontrol_news, 1);
> >  	} else {
> >  		/* non enumerated widget mixer */
> >  		for (i = 0; i < w->num_kcontrols; i++) {
> > @@ -490,7 +500,7 @@ static void remove_widget(struct snd_soc_component *comp,
> >  			snd_ctl_remove(card, w->kcontrols[i]);
> >  			kfree(sm);
> >  		}
> > -		kfree(w->kcontrol_news);
> > +		free_kcontrol_news(w->kcontrol_news, w->num_kcontrols);
> Hi Takashi,
> 
> I have not tested this patch yet. But it should fix the oops. Just looking
> the code I find remove_widget is either called from snd_soc_tplg_widget_remove
> or from snd_soc_tplg_component_remove. The xxx_component_remove is called
> during unregister of the component and there is no caller to
> snd_soc_tplg_widget_remove.
> 
> I guess the intention here is to free the kcontrol_news immediately after the
> card is registered. Please correct me if I am wrong.

It is already freed in the original code.  The only addition is to
free the newly allocated strings in kcontrol_news.  So kfree() is
replaced with free_kcontrol_news().

> Otherwise shouldn't the devm version of kstrdup work good as it just frees
> the memory when the device is removed?

No, as already mentioned, devm won't release the data until unbind and
the topology data might be reloaded repeatedly, thus user can hog the
kernel memory unlimitedly.


Takashi

> 
> Regards,
> Subhransu
> >  	}
> >  	/* widget w is freed by soc-dapm.c */
> >  }
> > @@ -1149,7 +1159,9 @@ static struct snd_kcontrol_new *soc_tplg_dapm_widget_dmixer_create(
> >  		dev_dbg(tplg->dev, " adding DAPM widget mixer control %s at %d\n",
> >  			mc->hdr.name, i);
> >  
> > -		kc[i].name = mc->hdr.name;
> > +		kc[i].name = kstrdup(mc->hdr.name, GFP_KERNEL);
> > +		if (!kc[i].name)
> > +			goto err_str;
> >  		kc[i].private_value = (long)sm;
> >  		kc[i].iface = SNDRV_CTL_ELEM_IFACE_MIXER;
> >  		kc[i].access = mc->hdr.access;
> > @@ -1196,7 +1208,7 @@ err_str:
> >  err:
> >  	for (--i; i >= 0; i--)
> >  		kfree((void *)kc[i].private_value);
> > -	kfree(kc);
> > +	free_kcontrol_news(kc, num_kcontrols);
> >  	return NULL;
> >  }
> >  
> > @@ -1228,7 +1240,9 @@ static struct snd_kcontrol_new *soc_tplg_dapm_widget_denum_create(
> >  	dev_dbg(tplg->dev, " adding DAPM widget enum control %s\n",
> >  		ec->hdr.name);
> >  
> > -	kc->name = ec->hdr.name;
> > +	kc->name = kstrdup(ec->hdr.name, GFP_KERNEL);
> > +	if (!kc->name)
> > +		goto err;
> >  	kc->private_value = (long)se;
> >  	kc->iface = SNDRV_CTL_ELEM_IFACE_MIXER;
> >  	kc->access = ec->hdr.access;
> > @@ -1294,7 +1308,7 @@ err_se:
> >  
> >  	kfree(se);
> >  err:
> > -	kfree(kc);
> > +	free_kcontrol_news(kc, 1);
> >  
> >  	return NULL;
> >  }
> > @@ -1330,7 +1344,9 @@ static struct snd_kcontrol_new *soc_tplg_dapm_widget_dbytes_create(
> >  			"ASoC: adding bytes kcontrol %s with access 0x%x\n",
> >  			be->hdr.name, be->hdr.access);
> >  
> > -		kc[i].name = be->hdr.name;
> > +		kc[i].name = kstrdup(be->hdr.name, GFP_KERNEL);
> > +		if (!kc[i].name)
> > +			goto err;
> >  		kc[i].private_value = (long)sbe;
> >  		kc[i].iface = SNDRV_CTL_ELEM_IFACE_MIXER;
> >  		kc[i].access = be->hdr.access;
> > @@ -1363,7 +1379,7 @@ err:
> >  	for (--i; i >= 0; i--)
> >  		kfree((void *)kc[i].private_value);
> >  
> > -	kfree(kc);
> > +	free_kcontrol_news(kc, count);
> >  	return NULL;
> >  }
> >  
> 
> -- 
>