Re: 2.6.16-rc regression: m68k CONFIG_RMW_INSNS=n compile broken

[Adrian Bunk <bunk@stusta.de>]

On Fri, Mar 03, 2006 at 03:22:42PM -0800, Linus Torvalds wrote:
> 
> 
> On Sat, 4 Mar 2006, Adrian Bunk wrote:
> > 
> > It seems the problem is that in the CONFIG_RMW_INSNS=n case, there's no 
> > cmpxchg #define in include/asm-m68k/system.h required for the 
> > atomic_add_unless #define in include/asm-m68k/atomic.h.
> 
> Hmm. It seems like it never has been there.. Do you know what brought this 
> on? Was it Nick's RCU changes from "rcuref_dec_and_test()" to 
> "atomic_dec_and_test()" and friends? 

It was Nick's commit 8426e1f6af0fd7f44d040af7263750c5a52f3cc3 that added 
atomic_inc_not_zero(), and Nick's patch that changed fs/file_table.c 
from rcuref_dec_and_test() to atomic_dec_and_test() exposed this 
problem.

> Judging by your error messages, I _think_ it's the "atomic_inc_not_zero()" 
> that gets expanded to a cmpxchg() that simply doesn't exist on m68k and 
> never has.

Exactly, that's what I wanted to say in my report.

> I guess we've never depended on cmpxchg before. Or am I missing something?

It seems this is the case.

And as far as I can see, m68k is the only architecture where cmpxchg 
isn't always available.

> 		Linus

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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