Messages in this thread | | | Date | Tue, 28 May 2019 15:14:00 +0800 | From | Gen Zhang <> | Subject | Re: [Question: devm_kfree] When should devm_kfree() be used? |
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On Tue, May 28, 2019 at 08:49:49AM +0200, Greg KH wrote: > 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 Yes, that is my question! I do have several patches about devm_kfree() and debate with maintainers. e.g. you can kindly refer to this lkml: https://lkml.org/lkml/2019/5/23/1547.
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.
And as mentioned above, e.g. hisi_sas_debugfs_init() in drivers/scsi/hisi_sas/hisi_sas_main.c, devm_kfree() is used to free devm_kmalloc().
So, thanks for looking into this, Greg.
Thanks Gen
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