[PATCH] riscv, atomic: Add #define's for the atomic_{cmp,}xchg_*() variants

From: Andrea Parri
Date: Fri Nov 30 2018 - 19:02:22 EST

If an architecture does not define the atomic_{cmp,}xchg_*() variants,
the generic implementation defaults them to the fully-ordered version.

riscv's had its own variants since "the beginning", but it never told
(#define-d these for) the generic implementation: it is time to do so.

Signed-off-by: Andrea Parri <andrea.parri@xxxxxxxxxxxxxxxxxxxx>
Cc: Palmer Dabbelt <palmer@xxxxxxxxxx>
Cc: Albert Ou <aou@xxxxxxxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
TBH, the delay was not intentional: I've just become aware of it while
working on moving riscv over to queued rwlocks. There's currently one
callsite for the non-fully-ordered variants mentioned above for riscv:
for atomic_cmpxchg_acquire() in kernel/sched/rt.c:rto_start_trylock(),


51a: 100726af lr.w a3,(a4)
51e: 00069763 bnez a3,52c <.L17>
522: 1af7262f sc.w.rl a2,a5,(a4)
526: fa75 bnez a2,51a <.L1>
528: 0330000f fence rw,rw


51a: 100726af lr.w a3,(a4)
51e: 00069763 bnez a3,52c <.L17>
522: 18f7262f sc.w a2,a5,(a4)
526: fa75 bnez a2,51a <.L1>
528: 0230000f fence r,rw

arch/riscv/include/asm/atomic.h | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/arch/riscv/include/asm/atomic.h b/arch/riscv/include/asm/atomic.h
index c452359c9cb8a..93826771b616a 100644
--- a/arch/riscv/include/asm/atomic.h
+++ b/arch/riscv/include/asm/atomic.h
@@ -303,6 +303,15 @@ c_t atomic##prefix##_cmpxchg(atomic##prefix##_t *v, c_t o, c_t n) \


+#define atomic_xchg_relaxed atomic_xchg_relaxed
+#define atomic_xchg_acquire atomic_xchg_acquire
+#define atomic_xchg_release atomic_xchg_release
+#define atomic_xchg atomic_xchg
+#define atomic_cmpxchg_relaxed atomic_cmpxchg_relaxed
+#define atomic_cmpxchg_acquire atomic_cmpxchg_acquire
+#define atomic_cmpxchg_release atomic_cmpxchg_release
+#define atomic_cmpxchg atomic_cmpxchg
#undef ATOMIC_OP