Make snd_card_free() a no-op again for NULL ptr argument

Make snd_card_free() a no-op again for NULL ptr argument

[Delio Brignoli]

Hello Takashi,

Commit “ALSA: Use standard device refcount for card accounting” <https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/sound/core/init.c?h=v4.12-rc6&id=f24640648186b59bd39f8cd640d631bdb61a3197> changed the behaviour of snd_card_free() in case of a NULL ptr argument. Before f24640648186b59bd39f8cd640d631bdb61a3197 snd_card_free() was a no-op in case of a NULL ptr argument as I would expect for a *_free() function. Currently passing a NULL ptr results in a NULL ptr dereference.

I believe the previous behaviour is worth restoring. If you agree I’ll follow up with a patch.

Thank you.
—
Delio



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Re: Make snd_card_free() a no-op again for NULL ptr argument

[Takashi Iwai]

On Thu, 29 Jun 2017 12:46:33 +0200,
Delio Brignoli wrote:
> 
> Hello Takashi,
> 
> Commit “ALSA: Use standard device refcount for card accounting” <https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/sound/core/init.c?h=v4.12-rc6&id=f24640648186b59bd39f8cd640d631bdb61a3197> changed the behaviour of snd_card_free() in case of a NULL ptr argument. Before f24640648186b59bd39f8cd640d631bdb61a3197 snd_card_free() was a no-op in case of a NULL ptr argument as I would expect for a *_free() function. Currently passing a NULL ptr results in a NULL ptr dereference.
> 
> I believe the previous behaviour is worth restoring. If you agree I’ll follow up with a patch.

In which situation do you need to pass NULL to snd_card_free()?


thanks,

Takashi
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Re: Make snd_card_free() a no-op again for NULL ptr argument

[Delio Brignoli]

> On 29 Jun 2017, at 12:49, Takashi Iwai <tiwai@suse.de> wrote:
> 
> On Thu, 29 Jun 2017 12:46:33 +0200,
> Delio Brignoli wrote:
>> 
>> Hello Takashi,
>> 
>> Commit “ALSA: Use standard device refcount for card accounting” <https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/sound/core/init.c?h=v4.12-rc6&id=f24640648186b59bd39f8cd640d631bdb61a3197> changed the behaviour of snd_card_free() in case of a NULL ptr argument. Before f24640648186b59bd39f8cd640d631bdb61a3197 snd_card_free() was a no-op in case of a NULL ptr argument as I would expect for a *_free() function. Currently passing a NULL ptr results in a NULL ptr dereference.
>> 
>> I believe the previous behaviour is worth restoring. If you agree I’ll follow up with a patch.
> 
> In which situation do you need to pass NULL to snd_card_free()?

Unconditional calls to snd_card_free(), similarly to unconditional calls to free().

struct snd_card *card = NULL;
…
/* setup code */
if (something_goes_wrong)
  goto cleanup;
…
retval = snd_card_new(…, &card);
…
cleanup:
  snd_card_free(card);
...

Sure, code can be re-organized to avoid it but *_free() function being a no-op in case of NULL ptr argument is the norm AFAIK. If so then why snd_card_free() should be different especially if it was doing the "right" thing before.

Thank you
--
Delio



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