linux-kernel - Re: [PATCH 1/5] ARM: add EXPORT_SYMBOL of hook_fault

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Date:	Mon, 8 Feb 2016 17:34:04 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Paul Gortmaker <paul.gortmaker@...driver.com>
Cc:	linux-kernel@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Ley Foon Tan <lftan@...era.com>,
	Arnd Bergmann <arnd@...db.de>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/5] ARM: add EXPORT_SYMBOL of hook_fault_code for PCI
 host modularization

On Sun, Feb 07, 2016 at 07:00:40PM -0500, Paul Gortmaker wrote:
> In a discussion of a previous patch set[1], it was suggested that
> modularizing some of the PCI host support would be good to keep
> multi platform bzImage sizes smaller.
> 
> Two of the files that are candidates for conversion to tristate
> from bool are:
> 
> drivers/pci/host/pci-imx6.c
> drivers/pci/host/pci-keystone.c
> 
> However, doing the conversion reveals that they are going to fail
> at modpost time since hook_fault_code isn't currently exported.
> 
> Since we are now going to export it we also need to remove the
> __init tag, as the fcn needs to be present at insmod time.
> 
> [1] https://lkml.kernel.org/r/20160108203102.GH5354@localhost
> 
> Cc: Russell King <linux@....linux.org.uk>
> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
> Cc: Thierry Reding <thierry.reding@...il.com>
> Cc: Ley Foon Tan <lftan@...era.com>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: linux-arm-kernel@...ts.infradead.org
> Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
> ---
>  arch/arm/mm/fault.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
> index daafcf121ce0..e0696a5ecc9b 100644
> --- a/arch/arm/mm/fault.c
> +++ b/arch/arm/mm/fault.c
> @@ -525,7 +525,7 @@ struct fsr_info {
>  #include "fsr-2level.c"
>  #endif
>  
> -void __init
> +void
>  hook_fault_code(int nr, int (*fn)(unsigned long, unsigned int, struct pt_regs *),
>  		int sig, int code, const char *name)
>  {
> @@ -537,6 +537,7 @@ hook_fault_code(int nr, int (*fn)(unsigned long, unsigned int, struct pt_regs *)
>  	fsr_info[nr].code = code;
>  	fsr_info[nr].name = name;
>  }
> +EXPORT_SYMBOL(hook_fault_code);

I'm really not a fan of this change - the hooks are supposed to remain
mostly static once the system is up and running, and should not change
at runtime (since there is no locking on these - see my previous reply.)
There's no protection (or support) for more than one function - iow, if
we have two modules trying to hook into the same fault code, the last
taker gets it (although the previous owner may get called given the
right timing.)

While it may be limited to two drivers at the moment, I'd like it to
remain that way.

If we really must have this, then please use EXPORT_SYMBOL_GPL() - I
don't want this interface to be used by code which isn't GPL compliant.

-- 
RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/
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