linux-kernel - Re: [PATCH] x86: fix improper .init-type section references

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Date:	Tue, 12 Jun 2007 17:39:10 +0530
From:	"Satyam Sharma" <satyam.sharma@...il.com>
To:	"Jan Beulich" <jbeulich@...ell.com>
Cc:	"Andi Kleen" <ak@...e.de>, linux-kernel@...r.kernel.org,
	patches@...-64.org, "Sam Ravnborg" <sam@...nborg.org>,
	"Venkatesh Pallipadi" <venkatesh.pallipadi@...el.com>
Subject: Re: [PATCH] x86: fix improper .init-type section references

Hi Jan,

On 6/12/07, Satyam Sharma <satyam.sharma@...il.com> wrote:
> On 6/12/07, Jan Beulich <jbeulich@...ell.com> wrote:
> > [...]
> > @@ -448,7 +448,7 @@ static void __cpuinit cache_shared_cpu_m
> > -static void __cpuinit cache_remove_shared_cpu_map(unsigned int cpu, int index)
> > +static void __cpuexit cache_remove_shared_cpu_map(unsigned int cpu, int index)
>
> You might've done this because the caller of
> cache_remove_shared_cpu_map() is cache_remove_dev()
> which is __cpuexit. However, cache_remove_dev() itself is called
> from cacheinfo_cpu_callback() which is ... __cpuinit, because it's
> caller cache_sysfs_init() is *definitely* __cpuinit. What a mess ...
>
> device_initcall(cache_sysfs_init):
>
> __cpuinit cache_sysfs_init
>   -> __cpuinit cacheinfo_cpu_callback  <======== PROBLEM
>     -> __cpuexit cache_remove_dev  <======== PROBLEM
>       -> __cpuinit cache_remove_shared_cpu_map
>
> Where cacheinfo_cpu_callback() itself is the callback for the
> cacheinfo_cpu_notifier notifier, which is itself marked __cpuinitdata.
>
> I suspect the __cpuexit-marking of cache_remove_dev() here is totally
> bogus. When !CONFIG_HOTPLUG_CPU, __cpuexit == __exit, and
> __exit simply means that the function can be discarded and ignored
> from being linked in for non-modular (built-in) build of that particular
> module. I'm not sure how the code in question here can ever be built
> as a module, so cache_remove_dev shouldn't be a __cpuexit in the
> first place. But not marking it anything would take us back to the
> modpost warnings. So ... something needs to be done about the
> logic in this whole place ...
>
> I did some more code inspection and found:
>
> The cacheinfo_cpu_notifier itself is called out from _cpu_down() which
> is ... yep, *not* __cpuinit (and obviously *cannot* be so). _cpu_down()
> is called from cpu_down() which is (thankfully!) protected inside
> #ifdef CONFIG_HOTPLUG_CPU, so we've /just about/ escaped trouble
> so far, but another of it's callers is disable_nonboot_cpus() which does
> *not* depend on HOTPLUG_CPU, but is #ifdef'ed inside SUSPEND_SMP
> (gargh!) instead, and ... is _not_ __cpuinit either (obviously, again).

Wait, SUSPEND_SMP again depends on HOTPLUG_CPU, so there
are no issues here in marking cache_remove_dev() __cpuexit
(which effectively simply becomes #ifdef HOTPLUG_CPU) as all
callsites that call out the notifier with CPU_DEAD/FROZEN are also
going to be disabled. [ Ok, looks like using __cpuexit as this kind of
pseudo-#ifdef HOTPLUG_CPU is a standard practice? ]

But modpost will still complain (bogus warning) about calling __exit
from __init (when HOTPLUG_CPU=n) for cacheinfo_cpu_callback()
calling cache_remove_dev(), no?

So I'd guess all the various notifier callback functions in your patch
need to be whitelisted by modpost, as those are __init functions
who can legally reference __exit (when HOTPLUG_CPU=n).
__init_refok can't be used here, so some special whitelisting might
be required, I presume.

Satyam
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