selftests/powerpc: Fix TM resched DSCR test with some compilers

[Michael Ellerman]

On Fri, 2017-05-19 at 01:37:45 UTC, Michael Ellerman wrote:
> The tm-resched-dscr test has started failing sometimes, depending on
> what compiler it's built with, eg:
> 
>   test: tm_resched_dscr
>   Check DSCR TM context switch: tm-resched-dscr: tm-resched-dscr.c:76: test_body: Assertion `rv' failed.
>   !! child died by signal 6
> 
> When it fails we see that the compiler doesn't initialise rv to 1 before
> entering the inline asm block. Although that's counter intuitive, it
> is allowed because we tell the compiler that the inline asm will write
> to rv (using "=r"), meaning the original value is irrelevant.
> 
> Marking it as a read/write parameter would presumably work, but it seems
> simpler to fix it by setting the initial value of rv in the inline asm.
> 
> Fixes: 96d016108640 ("powerpc: Correct DSCR during TM context switch")
> Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
> Acked-by: Michael Neuling <mikey at neuling.org>

Applied to powerpc fixes.

https://git.kernel.org/powerpc/c/fe06fe860250a4f01d0eaf70a2563b

cheers