Re: [PATCH] futex: Set USER_DS for the futex_detect_cmpxchg() test

[Andy Lutomirski]

> On Sep 28, 2018, at 1:26 PM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> 
>> On Fri, 28 Sep 2018, Max Filippov wrote:
>> 
>>> On Fri, Sep 28, 2018 at 11:02 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>>> There may be a much nicer solution.  Unless I missed something, only
>>> mips and xtensa even have the possibility of cmpxchg being missing.
>>> We could just make those arches supply a futex-detecting helper.
>> 
>> In case of xtensa availability of cmpxchg is known at build time.
> 
> That makes it even simpler. Could you provide a patch which selects
> CONFIG_HAVE_FUTEX_CMPXCHG for the right set of CPUs please?
> 
> 

I think thatâs the wrong approach, since it wonât cover mips. How about adding this to mips and xtensa only:

static inline void arch_have_futex_cmpxchg(void) {...};
#define arch_have_futex_cmpxchg arch_have_futex_cmpxchg

And getting rid of the config option.