linux-kernel - Re: [Question: devm_kfree] When should devm

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Message-ID: <20190528064949.GC2428@kroah.com>
Date:   Tue, 28 May 2019 08:49:49 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Gen Zhang <blackgod016574@...il.com>
Cc:     rafael@...nel.org, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [Question: devm_kfree] When should devm_kfree() be used?

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()?

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.

Do you have a driver that you think uses it incorrectly?

thanks,

greg k-h