Re: [PATCH v2 2/2] riscv/atomic: Strengthen implementations with fences

From: Palmer Dabbelt
Date: Fri Mar 09 2018 - 12:56:32 EST

On Fri, 09 Mar 2018 04:13:40 PST (-0800), parri.andrea@xxxxxxxxx wrote:
Atomics present the same issue with locking: release and acquire
variants need to be strengthened to meet the constraints defined
by the Linux-kernel memory consistency model [1].

Atomics present a further issue: implementations of atomics such
as atomic_cmpxchg() and atomic_add_unless() rely on LR/SC pairs,
which do not give full-ordering with .aqrl; for example, current
implementations allow the "lr-sc-aqrl-pair-vs-full-barrier" test
below to end up with the state indicated in the "exists" clause.

In order to "synchronize" LKMM and RISC-V's implementation, this
commit strengthens the implementations of the atomics operations
by replacing .rl and .aq with the use of ("lightweigth") fences,
and by replacing .aqrl LR/SC pairs in sequences such as:

0: lr.w.aqrl %0, %addr
bne %0, %old, 1f
...
sc.w.aqrl %1, %new, %addr
bnez %1, 0b
1:

with sequences of the form:

0: lr.w %0, %addr
bne %0, %old, 1f
...
sc.w.rl %1, %new, %addr /* SC-release */
bnez %1, 0b
fence rw, rw /* "full" fence */
1:

following Daniel's suggestion.

These modifications were validated with simulation of the RISC-V
memory consistency model.

C lr-sc-aqrl-pair-vs-full-barrier

{}

P0(int *x, int *y, atomic_t *u)
{
int r0;
int r1;

WRITE_ONCE(*x, 1);
r0 = atomic_cmpxchg(u, 0, 1);
r1 = READ_ONCE(*y);
}

P1(int *x, int *y, atomic_t *v)
{
int r0;
int r1;

WRITE_ONCE(*y, 1);
r0 = atomic_cmpxchg(v, 0, 1);
r1 = READ_ONCE(*x);
}

exists (u=1 /\ v=1 /\ 0:r1=0 /\ 1:r1=0)

[1] https://marc.info/?l=linux-kernel&m=151930201102853&w=2
https://groups.google.com/a/groups.riscv.org/forum/#!topic/isa-dev/hKywNHBkAXM
https://marc.info/?l=linux-kernel&m=151633436614259&w=2

Suggested-by: Daniel Lustig <dlustig@xxxxxxxxxx>
Signed-off-by: Andrea Parri <parri.andrea@xxxxxxxxx>
Cc: Palmer Dabbelt <palmer@xxxxxxxxxx>
Cc: Albert Ou <albert@xxxxxxxxxx>
Cc: Daniel Lustig <dlustig@xxxxxxxxxx>
Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: Jade Alglave <j.alglave@xxxxxxxxx>
Cc: Luc Maranget <luc.maranget@xxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Akira Yokosawa <akiyks@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: linux-riscv@xxxxxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
arch/riscv/include/asm/atomic.h | 417 +++++++++++++++++++++++++--------------
arch/riscv/include/asm/cmpxchg.h | 391 +++++++++++++++++++++++++++++-------
2 files changed, 588 insertions(+), 220 deletions(-)

diff --git a/arch/riscv/include/asm/atomic.h b/arch/riscv/include/asm/atomic.h
index e65d1cd89e28b..855115ace98c8 100644
--- a/arch/riscv/include/asm/atomic.h
+++ b/arch/riscv/include/asm/atomic.h
@@ -24,6 +24,20 @@
#include <asm/barrier.h>

#define ATOMIC_INIT(i) { (i) }
+
+#define __atomic_op_acquire(op, args...) \
+({ \
+ typeof(op##_relaxed(args)) __ret = op##_relaxed(args); \
+ __asm__ __volatile__(RISCV_ACQUIRE_BARRIER "" ::: "memory"); \
+ __ret; \
+})
+
+#define __atomic_op_release(op, args...) \
+({ \
+ __asm__ __volatile__(RISCV_RELEASE_BARRIER "" ::: "memory"); \
+ op##_relaxed(args); \
+})
+
static __always_inline int atomic_read(const atomic_t *v)
{
return READ_ONCE(v->counter);
@@ -50,22 +64,23 @@ static __always_inline void atomic64_set(atomic64_t *v, long i)
* have the AQ or RL bits set. These don't return anything, so there's only
* one version to worry about.
*/
-#define ATOMIC_OP(op, asm_op, I, asm_type, c_type, prefix) \
-static __always_inline void atomic##prefix##_##op(c_type i, atomic##prefix##_t *v) \
-{ \
- __asm__ __volatile__ ( \
- "amo" #asm_op "." #asm_type " zero, %1, %0" \
- : "+A" (v->counter) \
- : "r" (I) \
- : "memory"); \
-}
+#define ATOMIC_OP(op, asm_op, I, asm_type, c_type, prefix) \
+static __always_inline \
+void atomic##prefix##_##op(c_type i, atomic##prefix##_t *v) \
+{ \
+ __asm__ __volatile__ ( \
+ " amo" #asm_op "." #asm_type " zero, %1, %0" \
+ : "+A" (v->counter) \
+ : "r" (I) \
+ : "memory"); \
+} \

Just to be sure: this is just a whitespace change, right?

#ifdef CONFIG_GENERIC_ATOMIC64
-#define ATOMIC_OPS(op, asm_op, I) \
+#define ATOMIC_OPS(op, asm_op, I) \
ATOMIC_OP (op, asm_op, I, w, int, )
#else
-#define ATOMIC_OPS(op, asm_op, I) \
- ATOMIC_OP (op, asm_op, I, w, int, ) \
+#define ATOMIC_OPS(op, asm_op, I) \
+ ATOMIC_OP (op, asm_op, I, w, int, ) \
ATOMIC_OP (op, asm_op, I, d, long, 64)
#endif

@@ -79,75 +94,115 @@ ATOMIC_OPS(xor, xor, i)
#undef ATOMIC_OPS

/*
- * Atomic ops that have ordered, relaxed, acquire, and relese variants.
+ * Atomic ops that have ordered, relaxed, acquire, and release variants.
* There's two flavors of these: the arithmatic ops have both fetch and return
* versions, while the logical ops only have fetch versions.
*/
-#define ATOMIC_FETCH_OP(op, asm_op, I, asm_or, c_or, asm_type, c_type, prefix) \
-static __always_inline c_type atomic##prefix##_fetch_##op##c_or(c_type i, atomic##prefix##_t *v) \
-{ \
- register c_type ret; \
- __asm__ __volatile__ ( \
- "amo" #asm_op "." #asm_type #asm_or " %1, %2, %0" \
- : "+A" (v->counter), "=r" (ret) \
- : "r" (I) \
- : "memory"); \
- return ret; \
+#define ATOMIC_FETCH_OP(op, asm_op, I, asm_type, c_type, prefix) \
+static __always_inline \
+c_type atomic##prefix##_fetch_##op##_relaxed(c_type i, \
+ atomic##prefix##_t *v) \
+{ \
+ register c_type ret; \
+ __asm__ __volatile__ ( \
+ " amo" #asm_op "." #asm_type " %1, %2, %0" \
+ : "+A" (v->counter), "=r" (ret) \
+ : "r" (I) \
+ : "memory"); \
+ return ret; \
+} \
+static __always_inline \
+c_type atomic##prefix##_fetch_##op(c_type i, atomic##prefix##_t *v) \
+{ \
+ register c_type ret; \
+ __asm__ __volatile__ ( \
+ " amo" #asm_op "." #asm_type ".aqrl %1, %2, %0" \
+ : "+A" (v->counter), "=r" (ret) \
+ : "r" (I) \
+ : "memory"); \
+ return ret; \
}

-#define ATOMIC_OP_RETURN(op, asm_op, c_op, I, asm_or, c_or, asm_type, c_type, prefix) \
-static __always_inline c_type atomic##prefix##_##op##_return##c_or(c_type i, atomic##prefix##_t *v) \
-{ \
- return atomic##prefix##_fetch_##op##c_or(i, v) c_op I; \
+#define ATOMIC_OP_RETURN(op, asm_op, c_op, I, asm_type, c_type, prefix) \
+static __always_inline \
+c_type atomic##prefix##_##op##_return_relaxed(c_type i, \
+ atomic##prefix##_t *v) \
+{ \
+ return atomic##prefix##_fetch_##op##_relaxed(i, v) c_op I; \
+} \
+static __always_inline \
+c_type atomic##prefix##_##op##_return(c_type i, atomic##prefix##_t *v) \
+{ \
+ return atomic##prefix##_fetch_##op(i, v) c_op I; \
}

#ifdef CONFIG_GENERIC_ATOMIC64
-#define ATOMIC_OPS(op, asm_op, c_op, I, asm_or, c_or) \
- ATOMIC_FETCH_OP (op, asm_op, I, asm_or, c_or, w, int, ) \
- ATOMIC_OP_RETURN(op, asm_op, c_op, I, asm_or, c_or, w, int, )
+#define ATOMIC_OPS(op, asm_op, c_op, I) \
+ ATOMIC_FETCH_OP( op, asm_op, I, w, int, ) \
+ ATOMIC_OP_RETURN(op, asm_op, c_op, I, w, int, )
#else
-#define ATOMIC_OPS(op, asm_op, c_op, I, asm_or, c_or) \
- ATOMIC_FETCH_OP (op, asm_op, I, asm_or, c_or, w, int, ) \
- ATOMIC_OP_RETURN(op, asm_op, c_op, I, asm_or, c_or, w, int, ) \
- ATOMIC_FETCH_OP (op, asm_op, I, asm_or, c_or, d, long, 64) \
- ATOMIC_OP_RETURN(op, asm_op, c_op, I, asm_or, c_or, d, long, 64)
+#define ATOMIC_OPS(op, asm_op, c_op, I) \
+ ATOMIC_FETCH_OP( op, asm_op, I, w, int, ) \
+ ATOMIC_OP_RETURN(op, asm_op, c_op, I, w, int, ) \
+ ATOMIC_FETCH_OP( op, asm_op, I, d, long, 64) \
+ ATOMIC_OP_RETURN(op, asm_op, c_op, I, d, long, 64)
#endif

-ATOMIC_OPS(add, add, +, i, , _relaxed)
-ATOMIC_OPS(add, add, +, i, .aq , _acquire)
-ATOMIC_OPS(add, add, +, i, .rl , _release)
-ATOMIC_OPS(add, add, +, i, .aqrl, )
+ATOMIC_OPS(add, add, +, i)
+ATOMIC_OPS(sub, add, +, -i)

Sorry, I must be missing something, but how do the acquire and release atomics
get generated with this new code?

+
+#define atomic_add_return_relaxed atomic_add_return_relaxed
+#define atomic_sub_return_relaxed atomic_sub_return_relaxed
+#define atomic_add_return atomic_add_return
+#define atomic_sub_return atomic_sub_return

-ATOMIC_OPS(sub, add, +, -i, , _relaxed)
-ATOMIC_OPS(sub, add, +, -i, .aq , _acquire)
-ATOMIC_OPS(sub, add, +, -i, .rl , _release)
-ATOMIC_OPS(sub, add, +, -i, .aqrl, )
+#define atomic_fetch_add_relaxed atomic_fetch_add_relaxed
+#define atomic_fetch_sub_relaxed atomic_fetch_sub_relaxed
+#define atomic_fetch_add atomic_fetch_add
+#define atomic_fetch_sub atomic_fetch_sub
+
+#ifndef CONFIG_GENERIC_ATOMIC64
+#define atomic64_add_return_relaxed atomic64_add_return_relaxed
+#define atomic64_sub_return_relaxed atomic64_sub_return_relaxed
+#define atomic64_add_return atomic64_add_return
+#define atomic64_sub_return atomic64_sub_return
+
+#define atomic64_fetch_add_relaxed atomic64_fetch_add_relaxed
+#define atomic64_fetch_sub_relaxed atomic64_fetch_sub_relaxed
+#define atomic64_fetch_add atomic64_fetch_add
+#define atomic64_fetch_sub atomic64_fetch_sub
+#endif

#undef ATOMIC_OPS

#ifdef CONFIG_GENERIC_ATOMIC64
-#define ATOMIC_OPS(op, asm_op, I, asm_or, c_or) \
- ATOMIC_FETCH_OP(op, asm_op, I, asm_or, c_or, w, int, )
+#define ATOMIC_OPS(op, asm_op, I) \
+ ATOMIC_FETCH_OP(op, asm_op, I, w, int, )
#else
-#define ATOMIC_OPS(op, asm_op, I, asm_or, c_or) \
- ATOMIC_FETCH_OP(op, asm_op, I, asm_or, c_or, w, int, ) \
- ATOMIC_FETCH_OP(op, asm_op, I, asm_or, c_or, d, long, 64)
+#define ATOMIC_OPS(op, asm_op, I) \
+ ATOMIC_FETCH_OP(op, asm_op, I, w, int, ) \
+ ATOMIC_FETCH_OP(op, asm_op, I, d, long, 64)
#endif

-ATOMIC_OPS(and, and, i, , _relaxed)
-ATOMIC_OPS(and, and, i, .aq , _acquire)
-ATOMIC_OPS(and, and, i, .rl , _release)
-ATOMIC_OPS(and, and, i, .aqrl, )
+ATOMIC_OPS(and, and, i)
+ATOMIC_OPS( or, or, i)
+ATOMIC_OPS(xor, xor, i)

-ATOMIC_OPS( or, or, i, , _relaxed)
-ATOMIC_OPS( or, or, i, .aq , _acquire)
-ATOMIC_OPS( or, or, i, .rl , _release)
-ATOMIC_OPS( or, or, i, .aqrl, )
+#define atomic_fetch_and_relaxed atomic_fetch_and_relaxed
+#define atomic_fetch_or_relaxed atomic_fetch_or_relaxed
+#define atomic_fetch_xor_relaxed atomic_fetch_xor_relaxed
+#define atomic_fetch_and atomic_fetch_and
+#define atomic_fetch_or atomic_fetch_or
+#define atomic_fetch_xor atomic_fetch_xor

-ATOMIC_OPS(xor, xor, i, , _relaxed)
-ATOMIC_OPS(xor, xor, i, .aq , _acquire)
-ATOMIC_OPS(xor, xor, i, .rl , _release)
-ATOMIC_OPS(xor, xor, i, .aqrl, )
+#ifndef CONFIG_GENERIC_ATOMIC64
+#define atomic64_fetch_and_relaxed atomic64_fetch_and_relaxed
+#define atomic64_fetch_or_relaxed atomic64_fetch_or_relaxed
+#define atomic64_fetch_xor_relaxed atomic64_fetch_xor_relaxed
+#define atomic64_fetch_and atomic64_fetch_and
+#define atomic64_fetch_or atomic64_fetch_or
+#define atomic64_fetch_xor atomic64_fetch_xor
+#endif

#undef ATOMIC_OPS

@@ -157,22 +212,24 @@ ATOMIC_OPS(xor, xor, i, .aqrl, )
/*
* The extra atomic operations that are constructed from one of the core
* AMO-based operations above (aside from sub, which is easier to fit above).
- * These are required to perform a barrier, but they're OK this way because
- * atomic_*_return is also required to perform a barrier.
+ * These are required to perform a full barrier, but they're OK this way
+ * because atomic_*_return is also required to perform a full barrier.
+ *
*/
-#define ATOMIC_OP(op, func_op, comp_op, I, c_type, prefix) \
-static __always_inline bool atomic##prefix##_##op(c_type i, atomic##prefix##_t *v) \
-{ \
- return atomic##prefix##_##func_op##_return(i, v) comp_op I; \
+#define ATOMIC_OP(op, func_op, comp_op, I, c_type, prefix) \
+static __always_inline \
+bool atomic##prefix##_##op(c_type i, atomic##prefix##_t *v) \
+{ \
+ return atomic##prefix##_##func_op##_return(i, v) comp_op I; \
}

#ifdef CONFIG_GENERIC_ATOMIC64
-#define ATOMIC_OPS(op, func_op, comp_op, I) \
- ATOMIC_OP (op, func_op, comp_op, I, int, )
+#define ATOMIC_OPS(op, func_op, comp_op, I) \
+ ATOMIC_OP(op, func_op, comp_op, I, int, )
#else
-#define ATOMIC_OPS(op, func_op, comp_op, I) \
- ATOMIC_OP (op, func_op, comp_op, I, int, ) \
- ATOMIC_OP (op, func_op, comp_op, I, long, 64)
+#define ATOMIC_OPS(op, func_op, comp_op, I) \
+ ATOMIC_OP(op, func_op, comp_op, I, int, ) \
+ ATOMIC_OP(op, func_op, comp_op, I, long, 64)
#endif

ATOMIC_OPS(add_and_test, add, ==, 0)
@@ -182,51 +239,87 @@ ATOMIC_OPS(add_negative, add, <, 0)
#undef ATOMIC_OP
#undef ATOMIC_OPS

-#define ATOMIC_OP(op, func_op, I, c_type, prefix) \
-static __always_inline void atomic##prefix##_##op(atomic##prefix##_t *v) \
-{ \
- atomic##prefix##_##func_op(I, v); \
+#define ATOMIC_OP(op, func_op, I, c_type, prefix) \
+static __always_inline \
+void atomic##prefix##_##op(atomic##prefix##_t *v) \
+{ \
+ atomic##prefix##_##func_op(I, v); \
}

-#define ATOMIC_FETCH_OP(op, func_op, I, c_type, prefix) \
-static __always_inline c_type atomic##prefix##_fetch_##op(atomic##prefix##_t *v) \
-{ \
- return atomic##prefix##_fetch_##func_op(I, v); \
+#define ATOMIC_FETCH_OP(op, func_op, I, c_type, prefix) \
+static __always_inline \
+c_type atomic##prefix##_fetch_##op##_relaxed(atomic##prefix##_t *v) \
+{ \
+ return atomic##prefix##_fetch_##func_op##_relaxed(I, v); \
+} \
+static __always_inline \
+c_type atomic##prefix##_fetch_##op(atomic##prefix##_t *v) \
+{ \
+ return atomic##prefix##_fetch_##func_op(I, v); \
}

-#define ATOMIC_OP_RETURN(op, asm_op, c_op, I, c_type, prefix) \
-static __always_inline c_type atomic##prefix##_##op##_return(atomic##prefix##_t *v) \
-{ \
- return atomic##prefix##_fetch_##op(v) c_op I; \
+#define ATOMIC_OP_RETURN(op, asm_op, c_op, I, c_type, prefix) \
+static __always_inline \
+c_type atomic##prefix##_##op##_return_relaxed(atomic##prefix##_t *v) \
+{ \
+ return atomic##prefix##_fetch_##op##_relaxed(v) c_op I; \
+} \
+static __always_inline \
+c_type atomic##prefix##_##op##_return(atomic##prefix##_t *v) \
+{ \
+ return atomic##prefix##_fetch_##op(v) c_op I; \
}

#ifdef CONFIG_GENERIC_ATOMIC64
-#define ATOMIC_OPS(op, asm_op, c_op, I) \
- ATOMIC_OP (op, asm_op, I, int, ) \
- ATOMIC_FETCH_OP (op, asm_op, I, int, ) \
+#define ATOMIC_OPS(op, asm_op, c_op, I) \
+ ATOMIC_OP( op, asm_op, I, int, ) \
+ ATOMIC_FETCH_OP( op, asm_op, I, int, ) \
ATOMIC_OP_RETURN(op, asm_op, c_op, I, int, )
#else
-#define ATOMIC_OPS(op, asm_op, c_op, I) \
- ATOMIC_OP (op, asm_op, I, int, ) \
- ATOMIC_FETCH_OP (op, asm_op, I, int, ) \
- ATOMIC_OP_RETURN(op, asm_op, c_op, I, int, ) \
- ATOMIC_OP (op, asm_op, I, long, 64) \
- ATOMIC_FETCH_OP (op, asm_op, I, long, 64) \
+#define ATOMIC_OPS(op, asm_op, c_op, I) \
+ ATOMIC_OP( op, asm_op, I, int, ) \
+ ATOMIC_FETCH_OP( op, asm_op, I, int, ) \
+ ATOMIC_OP_RETURN(op, asm_op, c_op, I, int, ) \
+ ATOMIC_OP( op, asm_op, I, long, 64) \
+ ATOMIC_FETCH_OP( op, asm_op, I, long, 64) \
ATOMIC_OP_RETURN(op, asm_op, c_op, I, long, 64)
#endif

ATOMIC_OPS(inc, add, +, 1)
ATOMIC_OPS(dec, add, +, -1)

+#define atomic_inc_return_relaxed atomic_inc_return_relaxed
+#define atomic_dec_return_relaxed atomic_dec_return_relaxed
+#define atomic_inc_return atomic_inc_return
+#define atomic_dec_return atomic_dec_return
+
+#define atomic_fetch_inc_relaxed atomic_fetch_inc_relaxed
+#define atomic_fetch_dec_relaxed atomic_fetch_dec_relaxed
+#define atomic_fetch_inc atomic_fetch_inc
+#define atomic_fetch_dec atomic_fetch_dec
+
+#ifndef CONFIG_GENERIC_ATOMIC64
+#define atomic64_inc_return_relaxed atomic64_inc_return_relaxed
+#define atomic64_dec_return_relaxed atomic64_dec_return_relaxed
+#define atomic64_inc_return atomic64_inc_return
+#define atomic64_dec_return atomic64_dec_return
+
+#define atomic64_fetch_inc_relaxed atomic64_fetch_inc_relaxed
+#define atomic64_fetch_dec_relaxed atomic64_fetch_dec_relaxed
+#define atomic64_fetch_inc atomic64_fetch_inc
+#define atomic64_fetch_dec atomic64_fetch_dec
+#endif
+
#undef ATOMIC_OPS
#undef ATOMIC_OP
#undef ATOMIC_FETCH_OP
#undef ATOMIC_OP_RETURN

-#define ATOMIC_OP(op, func_op, comp_op, I, prefix) \
-static __always_inline bool atomic##prefix##_##op(atomic##prefix##_t *v) \
-{ \
- return atomic##prefix##_##func_op##_return(v) comp_op I; \
+#define ATOMIC_OP(op, func_op, comp_op, I, prefix) \
+static __always_inline \
+bool atomic##prefix##_##op(atomic##prefix##_t *v) \
+{ \
+ return atomic##prefix##_##func_op##_return(v) comp_op I; \
}

ATOMIC_OP(inc_and_test, inc, ==, 0, )
@@ -238,19 +331,19 @@ ATOMIC_OP(dec_and_test, dec, ==, 0, 64)

#undef ATOMIC_OP

-/* This is required to provide a barrier on success. */
+/* This is required to provide a full barrier on success. */
static __always_inline int __atomic_add_unless(atomic_t *v, int a, int u)
{
int prev, rc;

__asm__ __volatile__ (
- "0:\n\t"
- "lr.w.aqrl %[p], %[c]\n\t"
- "beq %[p], %[u], 1f\n\t"
- "add %[rc], %[p], %[a]\n\t"
- "sc.w.aqrl %[rc], %[rc], %[c]\n\t"
- "bnez %[rc], 0b\n\t"
- "1:"
+ "0: lr.w %[p], %[c]\n"
+ " beq %[p], %[u], 1f\n"
+ " add %[rc], %[p], %[a]\n"
+ " sc.w.rl %[rc], %[rc], %[c]\n"
+ " bnez %[rc], 0b\n"
+ " fence rw, rw\n"
+ "1:\n"
: [p]"=&r" (prev), [rc]"=&r" (rc), [c]"+A" (v->counter)
: [a]"r" (a), [u]"r" (u)
: "memory");
@@ -263,13 +356,13 @@ static __always_inline long __atomic64_add_unless(atomic64_t *v, long a, long u)
long prev, rc;

__asm__ __volatile__ (
- "0:\n\t"
- "lr.d.aqrl %[p], %[c]\n\t"
- "beq %[p], %[u], 1f\n\t"
- "add %[rc], %[p], %[a]\n\t"
- "sc.d.aqrl %[rc], %[rc], %[c]\n\t"
- "bnez %[rc], 0b\n\t"
- "1:"
+ "0: lr.d %[p], %[c]\n"
+ " beq %[p], %[u], 1f\n"
+ " add %[rc], %[p], %[a]\n"
+ " sc.d.rl %[rc], %[rc], %[c]\n"
+ " bnez %[rc], 0b\n"
+ " fence rw, rw\n"
+ "1:\n"
: [p]"=&r" (prev), [rc]"=&r" (rc), [c]"+A" (v->counter)
: [a]"r" (a), [u]"r" (u)
: "memory");
@@ -300,37 +393,63 @@ static __always_inline long atomic64_inc_not_zero(atomic64_t *v)

/*
* atomic_{cmp,}xchg is required to have exactly the same ordering semantics as
- * {cmp,}xchg and the operations that return, so they need a barrier.
- */
-/*
- * FIXME: atomic_cmpxchg_{acquire,release,relaxed} are all implemented by
- * assigning the same barrier to both the LR and SC operations, but that might
- * not make any sense. We're waiting on a memory model specification to
- * determine exactly what the right thing to do is here.
+ * {cmp,}xchg and the operations that return, so they need a full barrier.
*/
-#define ATOMIC_OP(c_t, prefix, c_or, size, asm_or) \
-static __always_inline c_t atomic##prefix##_cmpxchg##c_or(atomic##prefix##_t *v, c_t o, c_t n) \
-{ \
- return __cmpxchg(&(v->counter), o, n, size, asm_or, asm_or); \
-} \
-static __always_inline c_t atomic##prefix##_xchg##c_or(atomic##prefix##_t *v, c_t n) \
-{ \
- return __xchg(n, &(v->counter), size, asm_or); \
+#define ATOMIC_OP(c_t, prefix, size) \
+static __always_inline \
+c_t atomic##prefix##_xchg_relaxed(atomic##prefix##_t *v, c_t n) \
+{ \
+ return __xchg_relaxed(&(v->counter), n, size); \
+} \
+static __always_inline \
+c_t atomic##prefix##_xchg_acquire(atomic##prefix##_t *v, c_t n) \
+{ \
+ return __xchg_acquire(&(v->counter), n, size); \
+} \
+static __always_inline \
+c_t atomic##prefix##_xchg_release(atomic##prefix##_t *v, c_t n) \
+{ \
+ return __xchg_release(&(v->counter), n, size); \
+} \
+static __always_inline \
+c_t atomic##prefix##_xchg(atomic##prefix##_t *v, c_t n) \
+{ \
+ return __xchg(&(v->counter), n, size); \
+} \
+static __always_inline \
+c_t atomic##prefix##_cmpxchg_relaxed(atomic##prefix##_t *v, \
+ c_t o, c_t n) \
+{ \
+ return __cmpxchg_relaxed(&(v->counter), o, n, size); \
+} \
+static __always_inline \
+c_t atomic##prefix##_cmpxchg_acquire(atomic##prefix##_t *v, \
+ c_t o, c_t n) \
+{ \
+ return __cmpxchg_acquire(&(v->counter), o, n, size); \
+} \
+static __always_inline \
+c_t atomic##prefix##_cmpxchg_release(atomic##prefix##_t *v, \
+ c_t o, c_t n) \
+{ \
+ return __cmpxchg_release(&(v->counter), o, n, size); \
+} \
+static __always_inline \
+c_t atomic##prefix##_cmpxchg(atomic##prefix##_t *v, c_t o, c_t n) \
+{ \
+ return __cmpxchg(&(v->counter), o, n, size); \
}

#ifdef CONFIG_GENERIC_ATOMIC64
-#define ATOMIC_OPS(c_or, asm_or) \
- ATOMIC_OP( int, , c_or, 4, asm_or)
+#define ATOMIC_OPS() \
+ ATOMIC_OP( int, , 4)
#else
-#define ATOMIC_OPS(c_or, asm_or) \
- ATOMIC_OP( int, , c_or, 4, asm_or) \
- ATOMIC_OP(long, 64, c_or, 8, asm_or)
+#define ATOMIC_OPS() \
+ ATOMIC_OP( int, , 4) \
+ ATOMIC_OP(long, 64, 8)
#endif

-ATOMIC_OPS( , .aqrl)
-ATOMIC_OPS(_acquire, .aq)
-ATOMIC_OPS(_release, .rl)
-ATOMIC_OPS(_relaxed, )
+ATOMIC_OPS()

#undef ATOMIC_OPS
#undef ATOMIC_OP
@@ -340,13 +459,13 @@ static __always_inline int atomic_sub_if_positive(atomic_t *v, int offset)
int prev, rc;

__asm__ __volatile__ (
- "0:\n\t"
- "lr.w.aqrl %[p], %[c]\n\t"
- "sub %[rc], %[p], %[o]\n\t"
- "bltz %[rc], 1f\n\t"
- "sc.w.aqrl %[rc], %[rc], %[c]\n\t"
- "bnez %[rc], 0b\n\t"
- "1:"
+ "0: lr.w %[p], %[c]\n"
+ " sub %[rc], %[p], %[o]\n"
+ " bltz %[rc], 1f\n"
+ " sc.w.rl %[rc], %[rc], %[c]\n"
+ " bnez %[rc], 0b\n"
+ " fence rw, rw\n"
+ "1:\n"
: [p]"=&r" (prev), [rc]"=&r" (rc), [c]"+A" (v->counter)
: [o]"r" (offset)
: "memory");
@@ -361,13 +480,13 @@ static __always_inline long atomic64_sub_if_positive(atomic64_t *v, int offset)
long prev, rc;

__asm__ __volatile__ (
- "0:\n\t"
- "lr.d.aqrl %[p], %[c]\n\t"
- "sub %[rc], %[p], %[o]\n\t"
- "bltz %[rc], 1f\n\t"
- "sc.d.aqrl %[rc], %[rc], %[c]\n\t"
- "bnez %[rc], 0b\n\t"
- "1:"
+ "0: lr.d %[p], %[c]\n"
+ " sub %[rc], %[p], %[o]\n"
+ " bltz %[rc], 1f\n"
+ " sc.d.rl %[rc], %[rc], %[c]\n"
+ " bnez %[rc], 0b\n"
+ " fence rw, rw\n"
+ "1:\n"
: [p]"=&r" (prev), [rc]"=&r" (rc), [c]"+A" (v->counter)
: [o]"r" (offset)
: "memory");
diff --git a/arch/riscv/include/asm/cmpxchg.h b/arch/riscv/include/asm/cmpxchg.h
index db249dbc7b976..c12833f7b6bd1 100644
--- a/arch/riscv/include/asm/cmpxchg.h
+++ b/arch/riscv/include/asm/cmpxchg.h
@@ -17,45 +17,153 @@
#include <linux/bug.h>

#include <asm/barrier.h>
+#include <asm/fence.h>

-#define __xchg(new, ptr, size, asm_or) \
-({ \
- __typeof__(ptr) __ptr = (ptr); \
- __typeof__(new) __new = (new); \
- __typeof__(*(ptr)) __ret; \
- switch (size) { \
- case 4: \
- __asm__ __volatile__ ( \
- "amoswap.w" #asm_or " %0, %2, %1" \
- : "=r" (__ret), "+A" (*__ptr) \
- : "r" (__new) \
- : "memory"); \
- break; \
- case 8: \
- __asm__ __volatile__ ( \
- "amoswap.d" #asm_or " %0, %2, %1" \
- : "=r" (__ret), "+A" (*__ptr) \
- : "r" (__new) \
- : "memory"); \
- break; \
- default: \
- BUILD_BUG(); \
- } \
- __ret; \
-})
-
-#define xchg(ptr, x) (__xchg((x), (ptr), sizeof(*(ptr)), .aqrl))
-
-#define xchg32(ptr, x) \
-({ \
- BUILD_BUG_ON(sizeof(*(ptr)) != 4); \
- xchg((ptr), (x)); \
-})
-
-#define xchg64(ptr, x) \
-({ \
- BUILD_BUG_ON(sizeof(*(ptr)) != 8); \
- xchg((ptr), (x)); \
+#define __xchg_relaxed(ptr, new, size) \
+({ \
+ __typeof__(ptr) __ptr = (ptr); \
+ __typeof__(new) __new = (new); \
+ __typeof__(*(ptr)) __ret; \
+ switch (size) { \
+ case 4: \
+ __asm__ __volatile__ ( \
+ " amoswap.w %0, %2, %1\n" \
+ : "=r" (__ret), "+A" (*__ptr) \
+ : "r" (__new) \
+ : "memory"); \
+ break; \
+ case 8: \
+ __asm__ __volatile__ ( \
+ " amoswap.d %0, %2, %1\n" \
+ : "=r" (__ret), "+A" (*__ptr) \
+ : "r" (__new) \
+ : "memory"); \
+ break; \
+ default: \
+ BUILD_BUG(); \
+ } \
+ __ret; \
+})
+
+#define xchg_relaxed(ptr, x) \
+({ \
+ __typeof__(*(ptr)) _x_ = (x); \
+ (__typeof__(*(ptr))) __xchg_relaxed((ptr), \
+ _x_, sizeof(*(ptr))); \
+})
+
+#define __xchg_acquire(ptr, new, size) \
+({ \
+ __typeof__(ptr) __ptr = (ptr); \
+ __typeof__(new) __new = (new); \
+ __typeof__(*(ptr)) __ret; \
+ switch (size) { \
+ case 4: \
+ __asm__ __volatile__ ( \
+ " amoswap.w %0, %2, %1\n" \
+ RISCV_ACQUIRE_BARRIER \
+ : "=r" (__ret), "+A" (*__ptr) \
+ : "r" (__new) \
+ : "memory"); \
+ break; \
+ case 8: \
+ __asm__ __volatile__ ( \
+ " amoswap.d %0, %2, %1\n" \
+ RISCV_ACQUIRE_BARRIER \
+ : "=r" (__ret), "+A" (*__ptr) \
+ : "r" (__new) \
+ : "memory"); \
+ break; \
+ default: \
+ BUILD_BUG(); \
+ } \
+ __ret; \
+})
+
+#define xchg_acquire(ptr, x) \
+({ \
+ __typeof__(*(ptr)) _x_ = (x); \
+ (__typeof__(*(ptr))) __xchg_acquire((ptr), \
+ _x_, sizeof(*(ptr))); \
+})
+
+#define __xchg_release(ptr, new, size) \
+({ \
+ __typeof__(ptr) __ptr = (ptr); \
+ __typeof__(new) __new = (new); \
+ __typeof__(*(ptr)) __ret; \
+ switch (size) { \
+ case 4: \
+ __asm__ __volatile__ ( \
+ RISCV_RELEASE_BARRIER \
+ " amoswap.w %0, %2, %1\n" \
+ : "=r" (__ret), "+A" (*__ptr) \
+ : "r" (__new) \
+ : "memory"); \
+ break; \
+ case 8: \
+ __asm__ __volatile__ ( \
+ RISCV_RELEASE_BARRIER \
+ " amoswap.d %0, %2, %1\n" \
+ : "=r" (__ret), "+A" (*__ptr) \
+ : "r" (__new) \
+ : "memory"); \
+ break; \
+ default: \
+ BUILD_BUG(); \
+ } \
+ __ret; \
+})
+
+#define xchg_release(ptr, x) \
+({ \
+ __typeof__(*(ptr)) _x_ = (x); \
+ (__typeof__(*(ptr))) __xchg_release((ptr), \
+ _x_, sizeof(*(ptr))); \
+})
+
+#define __xchg(ptr, new, size) \
+({ \
+ __typeof__(ptr) __ptr = (ptr); \
+ __typeof__(new) __new = (new); \
+ __typeof__(*(ptr)) __ret; \
+ switch (size) { \
+ case 4: \
+ __asm__ __volatile__ ( \
+ " amoswap.w.aqrl %0, %2, %1\n" \
+ : "=r" (__ret), "+A" (*__ptr) \
+ : "r" (__new) \
+ : "memory"); \
+ break; \
+ case 8: \
+ __asm__ __volatile__ ( \
+ " amoswap.d.aqrl %0, %2, %1\n" \
+ : "=r" (__ret), "+A" (*__ptr) \
+ : "r" (__new) \
+ : "memory"); \
+ break; \
+ default: \
+ BUILD_BUG(); \
+ } \
+ __ret; \
+})
+
+#define xchg(ptr, x) \
+({ \
+ __typeof__(*(ptr)) _x_ = (x); \
+ (__typeof__(*(ptr))) __xchg((ptr), _x_, sizeof(*(ptr))); \
+})
+
+#define xchg32(ptr, x) \
+({ \
+ BUILD_BUG_ON(sizeof(*(ptr)) != 4); \
+ xchg((ptr), (x)); \
+})
+
+#define xchg64(ptr, x) \
+({ \
+ BUILD_BUG_ON(sizeof(*(ptr)) != 8); \
+ xchg((ptr), (x)); \
})

/*
@@ -63,7 +171,51 @@
* store NEW in MEM. Return the initial value in MEM. Success is
* indicated by comparing RETURN with OLD.
*/
-#define __cmpxchg(ptr, old, new, size, lrb, scb) \
+#define __cmpxchg_relaxed(ptr, old, new, size) \
+({ \
+ __typeof__(ptr) __ptr = (ptr); \
+ __typeof__(*(ptr)) __old = (old); \
+ __typeof__(*(ptr)) __new = (new); \
+ __typeof__(*(ptr)) __ret; \
+ register unsigned int __rc; \
+ switch (size) { \
+ case 4: \
+ __asm__ __volatile__ ( \
+ "0: lr.w %0, %2\n" \
+ " bne %0, %z3, 1f\n" \
+ " sc.w %1, %z4, %2\n" \
+ " bnez %1, 0b\n" \
+ "1:\n" \
+ : "=&r" (__ret), "=&r" (__rc), "+A" (*__ptr) \
+ : "rJ" (__old), "rJ" (__new) \
+ : "memory"); \
+ break; \
+ case 8: \
+ __asm__ __volatile__ ( \
+ "0: lr.d %0, %2\n" \
+ " bne %0, %z3, 1f\n" \
+ " sc.d %1, %z4, %2\n" \
+ " bnez %1, 0b\n" \
+ "1:\n" \
+ : "=&r" (__ret), "=&r" (__rc), "+A" (*__ptr) \
+ : "rJ" (__old), "rJ" (__new) \
+ : "memory"); \
+ break; \
+ default: \
+ BUILD_BUG(); \
+ } \
+ __ret; \
+})
+
+#define cmpxchg_relaxed(ptr, o, n) \
+({ \
+ __typeof__(*(ptr)) _o_ = (o); \
+ __typeof__(*(ptr)) _n_ = (n); \
+ (__typeof__(*(ptr))) __cmpxchg_relaxed((ptr), \
+ _o_, _n_, sizeof(*(ptr))); \
+})
+
+#define __cmpxchg_acquire(ptr, old, new, size) \
({ \
__typeof__(ptr) __ptr = (ptr); \
__typeof__(*(ptr)) __old = (old); \
@@ -73,24 +225,24 @@
switch (size) { \
case 4: \
__asm__ __volatile__ ( \
- "0:" \
- "lr.w" #scb " %0, %2\n" \
- "bne %0, %z3, 1f\n" \
- "sc.w" #lrb " %1, %z4, %2\n" \
- "bnez %1, 0b\n" \
- "1:" \
+ "0: lr.w %0, %2\n" \
+ " bne %0, %z3, 1f\n" \
+ " sc.w %1, %z4, %2\n" \
+ " bnez %1, 0b\n" \
+ RISCV_ACQUIRE_BARRIER \
+ "1:\n" \
: "=&r" (__ret), "=&r" (__rc), "+A" (*__ptr) \
: "rJ" (__old), "rJ" (__new) \
: "memory"); \
break; \
case 8: \
__asm__ __volatile__ ( \
- "0:" \
- "lr.d" #scb " %0, %2\n" \
- "bne %0, %z3, 1f\n" \
- "sc.d" #lrb " %1, %z4, %2\n" \
- "bnez %1, 0b\n" \
- "1:" \
+ "0: lr.d %0, %2\n" \
+ " bne %0, %z3, 1f\n" \
+ " sc.d %1, %z4, %2\n" \
+ " bnez %1, 0b\n" \
+ RISCV_ACQUIRE_BARRIER \
+ "1:\n" \
: "=&r" (__ret), "=&r" (__rc), "+A" (*__ptr) \
: "rJ" (__old), "rJ" (__new) \
: "memory"); \
@@ -101,34 +253,131 @@
__ret; \
})

-#define cmpxchg(ptr, o, n) \
- (__cmpxchg((ptr), (o), (n), sizeof(*(ptr)), .aqrl, .aqrl))
+#define cmpxchg_acquire(ptr, o, n) \
+({ \
+ __typeof__(*(ptr)) _o_ = (o); \
+ __typeof__(*(ptr)) _n_ = (n); \
+ (__typeof__(*(ptr))) __cmpxchg_acquire((ptr), \
+ _o_, _n_, sizeof(*(ptr))); \
+})

-#define cmpxchg_local(ptr, o, n) \
- (__cmpxchg((ptr), (o), (n), sizeof(*(ptr)), , ))
+#define __cmpxchg_release(ptr, old, new, size) \
+({ \
+ __typeof__(ptr) __ptr = (ptr); \
+ __typeof__(*(ptr)) __old = (old); \
+ __typeof__(*(ptr)) __new = (new); \
+ __typeof__(*(ptr)) __ret; \
+ register unsigned int __rc; \
+ switch (size) { \
+ case 4: \
+ __asm__ __volatile__ ( \
+ RISCV_RELEASE_BARRIER \
+ "0: lr.w %0, %2\n" \
+ " bne %0, %z3, 1f\n" \
+ " sc.w %1, %z4, %2\n" \
+ " bnez %1, 0b\n" \
+ "1:\n" \
+ : "=&r" (__ret), "=&r" (__rc), "+A" (*__ptr) \
+ : "rJ" (__old), "rJ" (__new) \
+ : "memory"); \
+ break; \
+ case 8: \
+ __asm__ __volatile__ ( \
+ RISCV_RELEASE_BARRIER \
+ "0: lr.d %0, %2\n" \
+ " bne %0, %z3, 1f\n" \
+ " sc.d %1, %z4, %2\n" \
+ " bnez %1, 0b\n" \
+ "1:\n" \
+ : "=&r" (__ret), "=&r" (__rc), "+A" (*__ptr) \
+ : "rJ" (__old), "rJ" (__new) \
+ : "memory"); \
+ break; \
+ default: \
+ BUILD_BUG(); \
+ } \
+ __ret; \
+})
+
+#define cmpxchg_release(ptr, o, n) \
+({ \
+ __typeof__(*(ptr)) _o_ = (o); \
+ __typeof__(*(ptr)) _n_ = (n); \
+ (__typeof__(*(ptr))) __cmpxchg_release((ptr), \
+ _o_, _n_, sizeof(*(ptr))); \
+})
+
+#define __cmpxchg(ptr, old, new, size) \
+({ \
+ __typeof__(ptr) __ptr = (ptr); \
+ __typeof__(*(ptr)) __old = (old); \
+ __typeof__(*(ptr)) __new = (new); \
+ __typeof__(*(ptr)) __ret; \
+ register unsigned int __rc; \
+ switch (size) { \
+ case 4: \
+ __asm__ __volatile__ ( \
+ "0: lr.w %0, %2\n" \
+ " bne %0, %z3, 1f\n" \
+ " sc.w.rl %1, %z4, %2\n" \
+ " bnez %1, 0b\n" \
+ " fence rw, rw\n" \
+ "1:\n" \
+ : "=&r" (__ret), "=&r" (__rc), "+A" (*__ptr) \
+ : "rJ" (__old), "rJ" (__new) \
+ : "memory"); \
+ break; \
+ case 8: \
+ __asm__ __volatile__ ( \
+ "0: lr.d %0, %2\n" \
+ " bne %0, %z3, 1f\n" \
+ " sc.d.rl %1, %z4, %2\n" \
+ " bnez %1, 0b\n" \
+ " fence rw, rw\n" \
+ "1:\n" \
+ : "=&r" (__ret), "=&r" (__rc), "+A" (*__ptr) \
+ : "rJ" (__old), "rJ" (__new) \
+ : "memory"); \
+ break; \
+ default: \
+ BUILD_BUG(); \
+ } \
+ __ret; \
+})

-#define cmpxchg32(ptr, o, n) \
-({ \
- BUILD_BUG_ON(sizeof(*(ptr)) != 4); \
- cmpxchg((ptr), (o), (n)); \
+#define cmpxchg(ptr, o, n) \
+({ \
+ __typeof__(*(ptr)) _o_ = (o); \
+ __typeof__(*(ptr)) _n_ = (n); \
+ (__typeof__(*(ptr))) __cmpxchg((ptr), \
+ _o_, _n_, sizeof(*(ptr))); \
})

-#define cmpxchg32_local(ptr, o, n) \
-({ \
- BUILD_BUG_ON(sizeof(*(ptr)) != 4); \
- cmpxchg_local((ptr), (o), (n)); \
+#define cmpxchg_local(ptr, o, n) \
+ (__cmpxchg_relaxed((ptr), (o), (n), sizeof(*(ptr))))
+
+#define cmpxchg32(ptr, o, n) \
+({ \
+ BUILD_BUG_ON(sizeof(*(ptr)) != 4); \
+ cmpxchg((ptr), (o), (n)); \
})

-#define cmpxchg64(ptr, o, n) \
-({ \
- BUILD_BUG_ON(sizeof(*(ptr)) != 8); \
- cmpxchg((ptr), (o), (n)); \
+#define cmpxchg32_local(ptr, o, n) \
+({ \
+ BUILD_BUG_ON(sizeof(*(ptr)) != 4); \
+ cmpxchg_relaxed((ptr), (o), (n)) \
})

-#define cmpxchg64_local(ptr, o, n) \
-({ \
- BUILD_BUG_ON(sizeof(*(ptr)) != 8); \
- cmpxchg_local((ptr), (o), (n)); \
+#define cmpxchg64(ptr, o, n) \
+({ \
+ BUILD_BUG_ON(sizeof(*(ptr)) != 8); \
+ cmpxchg((ptr), (o), (n)); \
+})
+
+#define cmpxchg64_local(ptr, o, n) \
+({ \
+ BUILD_BUG_ON(sizeof(*(ptr)) != 8); \
+ cmpxchg_relaxed((ptr), (o), (n)); \
})

#endif /* _ASM_RISCV_CMPXCHG_H */