[PATCH] lockdep: warn about lockdep disabling after kernel taint,fix

[Ingo Molnar]

* Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> wrote:

> Hi all,
> 
> Today's linux-next build (sparc defconfig) failed like this:
> 
> In file included from kernel/panic.c:12:
> include/linux/debug_locks.h: In function '__debug_locks_off':
> include/linux/debug_locks.h:15: error: implicit declaration of function 'xchg'
> 
> Caused by commit 9eeba6138cefc0435695463ddadb0d95e0a6bcd2 ("lockdep: warn
> about lockdep disabling after kernel taint").  xchg is defined in
> asm/system.h on sparc. It looks like asm/atomic.h on 64bit sparc includes
> asm/system.h, but not on 32bit.
> 
> Dave, arch/sparc/include/asm/atomic_32.h should really include
> asm/system.h since xchg is used in there.
> 
> I have applied the following patch for today.

I dont think Sparc is at fault here - system.h is where we 
historically provided xchg() from. Then as atomic.h was introduced 
and extended, some architectures (x86 amongst them) gradually 
migrated their definition of xchg() into atomic.h and related helper 
headers. (while still making it available for system.h)

This opened up the path for someone eventually only including 
asm/atomic.h from generic code and breaking the architectures that 
only provide it via system.h. So i've queued up the fix below - this 
should address the problem on Sparc and s390.

So moving it to atomic.h does make sense - but that's no excuse for 
breaking the build. Sorry about this!

	Ingo

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