Re: devm_spi_register_master

[Julia Lawall <julia.lawall-L2FTfq7BK8M@public.gmane.org>]

On Tue, 12 Nov 2013, Jingoo Han wrote:

> On Tuesday, November 12, 2013 2:45 AM, Julia Lawall wrote:
> >
> > Hello,
> >
> > I was looking into the use of devm_spi_register_master.  This function
> > seems to take care of registering and unregistering, but not allocation
> > and freeing.  I have the impression that that is done with
> > spi_alloc_master and and spi_master_put, which are not managed functions.
> > But then I wonder how this can work?  It seems that the spi_master_put
> > function should remain in the probe or remove function, and then the
> > object could be freed before it is unregistered?
> >
> > The patch 2fe7e4add3e53df7c1b97e32076f8390dd81c6b3 introduces a call to
> > devm_spi_register_master and also removes a call to spi_master_put.  By my
> > reasoning, this would cause a memory leak.
>
> Hi Julia Lawall,
>
> I already checked that the patch 2fe7e4a "spi: txx9: use
> devm_spi_register_master()" is right. The call to spi_master_put()
> was duplicated. So, it should be removed.
>
> When removing the driver, the following functions are called.
> : devm_spi_unregister()
>        -> spi_unregister_master()
>            -> device_unregister()
>                -> put_device()
>
> Also, spi_master_put() calls the following functions.
> : spi_master_put()
>        -> put_device()
>
> So, put_device() is duplicated, when devm_spi_register_master()
> is used. In this case, spi_master_put() can be removed.

spi_register_master calls device_add, which seems to increment the
reference count.  So it may be that both calls to put_device are needed.
On the other hand, in that case it would be safe to invert their order.

julia

> Mark,
> If I am wrong, please let me know kindly. :-)
>
> Best regards,
> Jingoo Han
>
>
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