linux-kernel - [PATCH] riscv, atomic: Add #define's for the atomic_{cmp,}xchg

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Date:   Sat,  1 Dec 2018 01:01:56 +0100
From:   Andrea Parri <andrea.parri@...rulasolutions.com>
To:     linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Cc:     Andrea Parri <andrea.parri@...rulasolutions.com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Will Deacon <will.deacon@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Boqun Feng <boqun.feng@...il.com>
Subject: [PATCH] riscv, atomic: Add #define's for the atomic_{cmp,}xchg_*() variants

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@...rulasolutions.com>
Cc: Palmer Dabbelt <palmer@...ive.com>
Cc: Albert Ou <aou@...s.berkeley.edu>
Cc: Will Deacon <will.deacon@....com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Boqun Feng <boqun.feng@...il.com>
---
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(),

[before]

     51a:	100726af          	lr.w	a3,(a4)
     51e:	00069763          	bnez	a3,52c <.L1.7>
     522:	1af7262f          	sc.w.rl	a2,a5,(a4)
     526:	fa75                	bnez	a2,51a <.L.1>
     528:	0330000f          	fence	rw,rw

[after]

     51a:	100726af          	lr.w	a3,(a4)
     51e:	00069763          	bnez	a3,52c <.L1.7>
     522:	18f7262f          	sc.w	a2,a5,(a4)
     526:	fa75                	bnez	a2,51a <.L.1>
     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)	\
 
 ATOMIC_OPS()
 
+#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_OPS
 #undef ATOMIC_OP
 
-- 
2.17.1