linux-kernel - Re: [PATCH] wlcore: spi: Fix a memory leaking bug in wl1271

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Message-ID: <20190528121452.GA23464@zhanggen-UX430UQ>
Date:   Tue, 28 May 2019 20:14:52 +0800
From:   Gen Zhang <blackgod016574@...il.com>
To:     Kalle Valo <kvalo@...eaurora.org>
Cc:     davem@...emloft.net, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] wlcore: spi: Fix a memory leaking bug in wl1271_probe()

On Tue, May 28, 2019 at 11:39:22AM +0000, Kalle Valo wrote:
> Gen Zhang <blackgod016574@...il.com> wrote:
> 
> > In wl1271_probe(), 'glue->core' is allocated by platform_device_alloc(),
> > when this allocation fails, ENOMEM is returned. However, 'pdev_data'
> > and 'glue' are allocated by devm_kzalloc() before 'glue->core'. When
> > platform_device_alloc() returns NULL, we should also free 'pdev_data'
> > and 'glue' before wl1271_probe() ends to prevent leaking memory.
> > 
> > Similarly, we shoulf free 'pdev_data' when 'glue' is NULL. And we should
> > free 'pdev_data' and 'glue' when 'glue->reg' is error and when 'ret' is
> > error.
> > 
> > Further, we should free 'glue->core', 'pdev_data' and 'glue' when this 
> > function normally ends to prevent leaking memory.
> > 
> > Signed-off-by: Gen Zhang <blackgod016574@...il.com>
> 
> Same questions as with similar SDIO patch:
> 
> https://patchwork.kernel.org/patch/10959049/
> 
> Patch set to Changes Requested.
> 
> -- 
> https://patchwork.kernel.org/patch/10959053/
> 
> https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches
> 
Thanks for your reply, Kalle. I had debate with Jon about this patch. 
You could kindly refer to lkml: https://lkml.org/lkml/2019/5/23/1547. 
And I don't think a practical conclusion is made there.

Further, I e-mailed Greg K-H about when should we use devm_kmalloc().

On Tue, May 28, 2019 at 08:32:57AM +0800, Gen Zhang wrote:
> devm_kmalloc() is used to allocate memory for a driver dev. Comments
> above the definition and doc 
> (https://www.kernel.org/doc/Documentation/driver-model/devres.txt) all
> imply that allocated the memory is automatically freed on driver attach,
> no matter allocation fail or not. However, I examined the code, and
> there are many sites that devm_kfree() is used to free devm_kmalloc().
> e.g. hisi_sas_debugfs_init() in drivers/scsi/hisi_sas/hisi_sas_main.c.
> So I am totally confused about this issue. Can anybody give me some
> guidance? When should we use devm_kfree()?
He replied: If you "know" you need to free the memory now, 
call devm_kfree(). If you want to wait for it to be cleaned up latter, 
like normal, then do not call it.

So could please look in to this issue?

Thanks
Gen