Re: devm_spi_register_master

[Jingoo Han <jg1.han-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>]

On Tuesday, November 12, 2013 12:19 PM, Julia Lawall wrote:
> On Tue, 12 Nov 2013, Jingoo Han wrote:
> > On Tuesday, November 12, 2013 2:45 AM, Julia Lawall wrote:
> > >
> > > 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.
> 

Hi Mark,

By the way, now I am testing s3c64xx by repeating modprobe & rmmod.
However, after s3c64xx_spi_remove() by rmmod, devm_spi_unregister()
is not called. So, at the next calling modprobe, it makes kernel panic.
On the other hand, When spi_unregister_master()& spi_master_put()
are added, the kernel panic does not happen.

Best regards,
Jingoo Han

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