On 24/05/2019 16:00, Gen Zhang wrote: > 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? There could well be cases where you need to explicitly call devm_kfree(), but having a quick glance at the example above, I don't see why you would call devm_kfree() here and yes looks like that code could be simplified significantly. Notice that hisi_sas_debugfs_exit() does not free any memory as it is not necessary to explicitly do so. Cheers Jon -- nvpublic
