provide atomic64_try_cmpxchg() for 32bit

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

2 files changed, 16 insertions, 0 deletions

diff --git a/include/linux/atomic.h b/include/linux/atomic.h
index dcc6e644..c594ff8b 100644
--- a/include/linux/atomic.h
+++ b/include/linux/atomic.h
@@ -344,6 +344,7 @@ void atomic64_sub(s64, atomic64_t *);
 
 s64 atomic64_xchg(atomic64_t *, s64);
 s64 atomic64_cmpxchg(atomic64_t *, s64, s64);
+bool atomic64_try_cmpxchg(atomic64_t *, s64 *, s64);
 
 #define atomic64_add_negative(a, v)	(atomic64_add_return((a), (v)) < 0)
 #define atomic64_inc(v)			atomic64_add(1LL, (v))
diff --git a/linux/atomic64.c b/linux/atomic64.c
index 4654d092..2dbbc995 100644
--- a/linux/atomic64.c
+++ b/linux/atomic64.c
@@ -157,6 +157,21 @@ long long atomic64_cmpxchg(atomic64_t *v, long long o, long long n)
 	return val;
 }
 
+bool atomic64_try_cmpxchg(atomic64_t *v, s64 *o, s64 n)
+{
+	unsigned long flags;
+	raw_spinlock_t *lock = lock_addr(v);
+
+	raw_spin_lock_irqsave(lock, flags);
+	bool ret = v->counter == *o;
+	if (ret)
+		v->counter = n;
+	else
+		*o = v->counter;
+	raw_spin_unlock_irqrestore(lock, flags);
+	return ret;
+}
+
 long long atomic64_xchg(atomic64_t *v, long long new)
 {
 	unsigned long flags;