linux-kernel - RE: RE: [PATCH v2 2/4] extcon: Added extcon_alloc_cables to simplify extcon register function

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Date:   Thu, 2 Mar 2023 17:33:12 +0900
From:   "Bumwoo Lee" <bw365.lee@...sung.com>
To:     <myungjoo.ham@...sung.com>,
        "'Chanwoo Choi'" <cw00.choi@...sung.com>,
        <linux-kernel@...r.kernel.org>
Subject: RE: RE: [PATCH v2 2/4] extcon: Added extcon_alloc_cables to
 simplify extcon register function


> -----Original Message-----
> From: Bumwoo Lee <bw365.lee@...sung.com>
> Sent: Thursday, March 2, 2023 4:12 PM
> To: 'myungjoo.ham@...sung.com' <myungjoo.ham@...sung.com>; 'Chanwoo Choi'
> <cw00.choi@...sung.com>; 'linux-kernel@...r.kernel.org' <linux-
> kernel@...r.kernel.org>
> Subject: RE: RE: [PATCH v2 2/4] extcon: Added extcon_alloc_cables to
> simplify extcon register function
> 
> 
> > -----Original Message-----
> > From: MyungJoo Ham <myungjoo.ham@...sung.com>
> > Sent: Thursday, March 2, 2023 3:33 PM
> > To: Bumwoo Lee <bw365.lee@...sung.com>; Chanwoo Choi
> > <cw00.choi@...sung.com>; linux-kernel@...r.kernel.org
> > Subject: RE: RE: [PATCH v2 2/4] extcon: Added extcon_alloc_cables to
> > simplify extcon register function
> >
> > >
> > >
> > >--------- Original Message ---------
> > >Sender : 이범우 <bw365.lee@...sung.com>Product S/W Lab(VD)/삼성전자 Date :
> > >2023-03-02 10:38 (GMT+9) Title : RE: [PATCH v2 2/4] extcon: Added
> > >extcon_alloc_cables to simplify extcon register function
> > >
> > >Hello.
> > >
> > >As you can see, edev->cables are freed if extcon_alloc_cables()
> > >function return error handling in extcon_dev_register() Other added
> > functions are also same.
> > >
> > >Because it's functionalized, apart from this, do you want to mention
> > >that
> > it should be freed within the function?
> > >Please let me know your opinion.
> > >
> > >extcon_dev_register(struct extcon_dev *edev){ ...
> > >
> > >        ret = extcon_alloc_cables(edev);
> > >        if (ret)
> > >                goto err_alloc_cables;
> > >
> > >...
> > >
> > >err_alloc_cables:
> > >         if (edev->max_supported)
> > >                 kfree(edev->cables);
> > >
> > >
> > >Regards,
> > >Bumwoo
> >
> > In such a case, you are doing kfree(NULL); with the following:
> 
> Yes, you are right.
> But Kfree() is checking NULL internally. So it does not a problem I think.
> Anyway I added kfree(edev->cables) before exit extcon_alloc_cables() like
> below on v3 patches.
> 
> static int extcon_alloc_cables(struct extcon_dev *edev) { ...
>                          for (index--; index >= 0; index--) {
>                                  cable = &edev->cables[index];
>                                  kfree(cable->attr_g.name);
>                          }
> 
> +                        kfree(edev->cables);
>                          return -ENOMEM;
>                  }
> 

In order to avoid unnecessary kfree(NULL), the position will be moved like below on v4 patch.

err_alloc_muex:
	for (index = 0; index < edev->max_supported; index++)
        	kfree(edev->cables[index].attr_g.name);
+	if (edev->max_supported)
+		kfree(edev->cables);
err_alloc_cables:
-	if (edev->max_supported)
-		kfree(edev->cables); 
        return ret;


> Regards,
> Bumwoo