Subject: Re: [PATCH] powerpc/fsl_pci: Fix pci stack build bug with FRAME_WARN

From: Scott Wood <[email-masked]>
Date: Wed, 21 Jan 2015 21:02:27 -0600

On Wed, 2015-01-21 at 20:48 -0600, Kim Phillips wrote:
> On Tue, 20 Jan 2015 18:31:32 -0600
> Scott Wood <[email-masked]> wrote:
> 
> > On Tue, 2015-01-20 at 14:03 -0600, Kim Phillips wrote:
> > > Fix this:
> > > 
> > >   CC      arch/powerpc/sysdev/fsl_pci.o
> > > arch/powerpc/sysdev/fsl_pci.c: In function 'fsl_pcie_check_link':
> > > arch/powerpc/sysdev/fsl_pci.c:91:1: error: the frame size of 1360 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]
> > > 
> > > when configuring FRAME_WARN, by converting the allocation from the
> > > stack to the heap.  We use GFP_ATOMIC since this function can be
> > > called with interrupts disabled.
> > > 
> > > Signed-off-by: Kim Phillips <[email-masked]>
> > > ---
> > >  arch/powerpc/sysdev/fsl_pci.c | 12 +++++++-----
> > >  1 file changed, 7 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/arch/powerpc/sysdev/fsl_pci.c b/arch/powerpc/sysdev/fsl_pci.c
> > > index 6455c1e..635d743 100644
> > > --- a/arch/powerpc/sysdev/fsl_pci.c
> > > +++ b/arch/powerpc/sysdev/fsl_pci.c
> > > @@ -69,11 +69,13 @@ static int fsl_pcie_check_link(struct pci_controller *hose)
> > >  
> > >  	if (hose->indirect_type & PPC_INDIRECT_TYPE_FSL_CFG_REG_LINK) {
> > >  		if (hose->ops->read == fsl_indirect_read_config) {
> > > -			struct pci_bus bus;
> > > -			bus.number = hose->first_busno;
> > > -			bus.sysdata = hose;
> > > -			bus.ops = hose->ops;
> > > -			indirect_read_config(&bus, 0, PCIE_LTSSM, 4, &val);
> > > +			struct pci_bus *bus;
> > > +			bus = kmalloc(sizeof(*bus), GFP_ATOMIC);
> > > +			bus->number = hose->first_busno;
> > 
> > Missing check for allocation failure.
> 
> thanks.
> 
> > Do we not have a real struct pci_bus we can use here?  Or refactor
> > indirect_read_config() to take hose and bus number instead?
> 
> indirect_read_config() can't be refactored because it is also used
> in the generic struct pci_ops.  Unless you mean making an
> __indirect_read_config that the original would call, 

Yes, that's what I mean.

> but that doesn't look that trivial given it calls pci_exclude_device with a
> struct pci_controller hose.

Check for excluded devices in indirect_read_config(), not
__indirect_read_config().

> > If putting a pci_bus struct on the stack is no longer OK, then
> > fake_pci_bus() should be fixed as well.  I wonder if GCC is allocating
> > separate pci_bus structs on the stack for this one and the one that
> > early_read_config_dword() uses...
> 
> fake_pci_bus()' version is static, so it's not on the stack.
> 
> given that, maybe fsl_pcie_check_link()'s should be static too?

Oh.  How would you ensure that it's only called once at a time?  It
doesn't look like this is only called during early boot.
fsl_pcie_check_link() is called every time we do any config read through
the normal interface.  This is also a concern for the call to
early_read_config_dword().

-Scott