MFC r329523 and r329524:

Fix implementation of xchg() function macro in the LinuxKPI.
The exchange operation must be atomic.

Sponsored by:	Mellanox Technologies

1 files changed, 35 insertions, 6 deletions

diff --git a/sys/compat/linuxkpi/common/include/asm/atomic.h b/sys/compat/linuxkpi/common/include/asm/atomic.h
index 3323e7d..4b2610c 100644
--- a/sys/compat/linuxkpi/common/include/asm/atomic.h
+++ b/sys/compat/linuxkpi/common/include/asm/atomic.h
@@ -198,12 +198,41 @@ atomic_cmpxchg(atomic_t *v, int old, int new)
 
 #define	cmpxchg_relaxed(...)	cmpxchg(__VA_ARGS__)
 
-#define	xchg(ptr, v) ({						\
-	__typeof(*(ptr)) __ret;					\
-								\
-	__ret = *(ptr);						\
-	*(ptr) = v;						\
-	__ret;							\
+#define	xchg(ptr, new) ({						\
+	union {								\
+		__typeof(*(ptr)) val;					\
+		u8 u8[0];						\
+		u16 u16[0];						\
+		u32 u32[0];						\
+		u64 u64[0];						\
+	} __ret, __new = { .val = (new) };				\
+									\
+	CTASSERT(sizeof(__ret.val) == 1 || sizeof(__ret.val) == 2 ||	\
+	    sizeof(__ret.val) == 4 || sizeof(__ret.val) == 8);		\
+									\
+	switch (sizeof(__ret.val)) {					\
+	case 1:								\
+		__ret.val = READ_ONCE(*ptr);				\
+		while (!atomic_fcmpset_8((volatile u8 *)(ptr),		\
+	            __ret.u8, __new.u8[0]))				\
+			;						\
+		break;							\
+	case 2:								\
+		__ret.val = READ_ONCE(*ptr);				\
+		while (!atomic_fcmpset_16((volatile u16 *)(ptr),	\
+	            __ret.u16, __new.u16[0]))				\
+			;						\
+		break;							\
+	case 4:								\
+		__ret.u32[0] = atomic_swap_32((volatile u32 *)(ptr),	\
+		    __new.u32[0]);					\
+		break;							\
+	case 8:								\
+		__ret.u64[0] = atomic_swap_64((volatile u64 *)(ptr),	\
+		    __new.u64[0]);					\
+		break;							\
+	}								\
+	__ret.val;							\
 })
 
 #define	LINUX_ATOMIC_OP(op, c_op)				\