[PATCH v2 06/11] powerpc: powernv: Fix KCSAN datarace warnings on idle_state contention

[Nicholas Piggin]

On Wed May 10, 2023 at 1:31 PM AEST, Rohan McLure wrote:
> The idle_state entry in the PACA on PowerNV features a bit which is
> atomically tested and set through ldarx/stdcx. to be used as a spinlock.
> This lock then guards access to other bit fields of idle_state. KCSAN
> cannot differentiate between any of these bitfield accesses as they all
> are implemented by 8-byte store/load instructions, thus cores contending
> on the bit-lock appear to data race with modifications to idle_state.
>
> Separate the bit-lock entry from the data guarded by the lock to avoid
> the possibility of data races being detected by KCSAN.
>
> Suggested-by: Nicholas Piggin <npiggin at gmail.com>
> Signed-off-by: Rohan McLure <rmclure at linux.ibm.com>

Reviewed-by: Nicholas Piggin <npiggin at gmail.com>