linux-kernel - Re: [PATCH] tegra_wm9712: Fix a memory leaking bug in tegra_wm9712_driver

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Message-ID: <20190524150053.GA9235@zhanggen-UX430UQ>
Date:   Fri, 24 May 2019 23:00:53 +0800
From:   Gen Zhang <blackgod016574@...il.com>
To:     Jon Hunter <jonathanh@...dia.com>
Cc:     lgirdwood@...il.com, perex@...ex.cz, alsa-devel@...a-project.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tegra_wm9712: Fix a memory leaking bug in
 tegra_wm9712_driver_probe()

On Fri, May 24, 2019 at 03:47:34PM +0100, Jon Hunter wrote:
> 
> On 24/05/2019 15:33, Gen Zhang wrote:
> > On Fri, May 24, 2019 at 09:33:13AM +0100, Jon Hunter wrote:
> >>
> >> On 24/05/2019 01:50, Gen Zhang wrote:
> >>> In tegra_wm9712_driver_probe(), 'machine->codec' is allocated by
> >>> platform_device_alloc(). When it is NULL, function returns ENOMEM.
> >>> However, 'machine' is allocated by devm_kzalloc() before this site.
> >>> Thus we should free 'machine' before function ends to prevent memory
> >>> leaking.
> >>
> >> Memory allocated by devm_xxx() is automatically freed on failure so this
> >> is not correct.
> > Thanks for your comments, Jon. But after I examined the code, I am still
> > confused about the usage of devm_kmalloc(). You can kindly refer to 
> > hisi_sas_debugfs_init() in drivers/scsi/hisi_sas/hisi_sas_main.c. And
> > devm_kfree() is used to free a memory allocated by devm_kmalloc(). And
> > I found other situations similar to this in other files.
> > 
> > So, I hope you can give me some guidance on this. Thanks!
> 
> Please refer to the devres documentation [0].
> 
> Cheers,
> Jon
> 
> [0] https://www.kernel.org/doc/Documentation/driver-model/devres.txt
> 
> -- 
> nvpublic
Thanks for your reply. I figured out that devm_kmalloc will free the 
memory no matter fail or not. But I still want to ask why other codes
as I above mentioned use devm_kfree() to free memory allocated by 
devm_kmalloc(). If the memory is automatically freed, is this 
devm_kfee() redundant codes that should be removed? Am I 
misunderstanding this again or it is something else?

Thanks
Gen