On Sun, 27 May 2007 11:56:21 +0200 Andi Kleen <[email protected]> wrote:
>
> >
> > So section mismatch warnings are more about catching sloopy usage of __init than it is to
> > catch potential kernel oopesen. But the latter is a nice side effect that is appreciated.
>
> My point was that I cannot recall a single real oops bug found by the compile
> time checking.
There are quite a few of these fixes where you look at it and wonder "ytf
did the kernel ever work"? I suspect that it's partly a case of the code
reading random junk from where a flag used to be and continuing to work.
CONFIG_DEBUG_PAGEALLOC would have caught it.
Also, simply lack of testing coverage: few people have the correct
hardware, the correct config options and then go and do an rmmod+insmod.
Even fewer do a CPU hotplug. Fewer still do a memory hotplug.
But there are a lot of fixes, and a lot of warnings, and they are real bugs.
> We had a few in the past, but since we poison init data after boot they all tended
> to be found quickly anyways.
Sometimes. But a common pattern is "discover something at boot time and
save it away for later boot-time code". The storage gets marked __fooinit
and then it turns out that some non-boot-time initialisation code is using
it.
> But the warnings just seem to require endless changes and bogus changes
> (randomly moving code which was actually ok because it only called
> in the init case).
That would be a false positive. We do need the various tools to suppress
those so that we can find new bugs as they turn up.
You're right that it's all a complete pain. But the fault doesn't lie with
the checking code, IMO. It's just that the whole initdata thing is hard to
get right. All this fuss for a couple hundred kbytes - any sane
organisation would have killed the whole thing years ago ;)
It'll really get to be fun when some smarty writes us a "non __init symbol
referred to only from __init code" checker.
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