Re: [PATCH v8 09/14] lockdep: Apply crossrelease to completions

[Arnd Bergmann]

On Sat, Aug 19, 2017 at 2:51 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote:

>> --- a/include/linux/completion.h
>> +++ b/include/linux/completion.h
>> @@ -74,7 +74,7 @@ static inline void complete_release_commit(struct completion *x) {}
>>  #endif
>>
>>  #define COMPLETION_INITIALIZER_ONSTACK(work) \
>> -       ({ init_completion(&work); work; })
>> +       (*({ init_completion(&work); &work; }))
>>
>>  /**
>>   * DECLARE_COMPLETION - declare and initialize a completion structure
>
> Nice hack. Any idea why that's different to the compiler?
>
> I've applied that one to my test tree now, and reverted my own patch,
> will let you know if anything else shows up. I think we probably want
> to merge both patches to mainline.

There is apparently one user of COMPLETION_INITIALIZER_ONSTACK
that causes a regression with the patch above:

drivers/acpi/nfit/core.c: In function 'acpi_nfit_flush_probe':
include/linux/completion.h:77:3: error: value computed is not used
[-Werror=unused-value]
  (*({ init_completion(&work); &work; }))

It would be trivial to convert to init_completion(), which seems to be
what was intended there.

        Arnd