linux-kernel - Re: Re: [PATCH] staging: greybus: audio: Check null pointer

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Message-Id: <20211228020221.1635885-1-jiasheng@iscas.ac.cn>
Date:   Tue, 28 Dec 2021 10:02:21 +0800
From:   Jiasheng Jiang <jiasheng@...as.ac.cn>
To:     vaibhav.sr@...il.com, mgreer@...malcreek.com, johan@...nel.org,
        elder@...nel.org, gregkh@...uxfoundation.org
Cc:     greybus-dev@...ts.linaro.org, linux-staging@...ts.linux.dev,
        linux-kernel@...r.kernel.org, Jiasheng Jiang <jiasheng@...as.ac.cn>
Subject: Re: Re: [PATCH] staging: greybus: audio: Check null pointer

Sorry the previous email is forgetten to wrap line.
This email is corrected and the content is the same.

On Mon, Dec 27, 2021 at 11:54:10PM +0800, Alex Elder wrote:
> I think this is a good change, but I would like you to improve
> the description, and fix some different bugs introduced by your
> change.
>
> What you are specifically doing is checking for a null return
> from devm_kcalloc() in gb_generate_enum_strings(), and are
> returning the NULL pointer if that occurs.  That means you
> need to update all the callers of gb_generate_enum_strings()
> to also handle a possible null return value.
>
> The fix does a good thing, and your description is correct
> about what you are fixing.  But it should supply more
> complete context for the change.

Thanks for your advice, I will correct my description in next version.
But I still have some question about the devm_kzalloc().

> You can't simply return here.  If you look a bit above this,
> where the call to allocate a control structure is done, you
> see that a NULL return there jumps to the "error" label, so
> any already allocated and initialized control widgets get
> cleaned up before returning.

Actually, I have already thought of whether it needs to free after the
devm_kzalloc().
As we can find in the gbaudio_tplg_create_widget(), the widget_kctls is
allocated by devm_kzalloc(), but isn't released when
gbaudio_tplg_create_wcontrol() fails and goto error.
And I check of the comment of the devm_kmalloc() in `drivers/base/devres.c`,
because devm_kzalloc() returns devm_kmalloc().
And it says that "Memory allocated with this function is automatically
freed on driver detach."
So there is no need to free the memory manually.
Is that right?
And I am sorry again because of the lack of the above explanation in my
commit message.
I will also add to my new commit.

Thanks,
Jiang