svn commit: r329523 - head/sys/compat/linuxkpi/common/include/asm

[Hans Petter Selasky]

Author: hselasky
Date: Sun Feb 18 17:37:23 2018
New Revision: 329523
URL: https://svnweb.freebsd.org/changeset/base/329523

Log:
  Fix implementation of xchg() function macro in the LinuxKPI.
  The exchange operation must be atomic.
  
  MFC after:	1 week
  Sponsored by:	Mellanox Technologies

Modified:
  head/sys/compat/linuxkpi/common/include/asm/atomic.h

Modified: head/sys/compat/linuxkpi/common/include/asm/atomic.h
==============================================================================
--- head/sys/compat/linuxkpi/common/include/asm/atomic.h	Sun Feb 18 16:41:34 2018	(r329522)
+++ head/sys/compat/linuxkpi/common/include/asm/atomic.h	Sun Feb 18 17:37:23 2018	(r329523)
@@ -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 = { .val = READ_ONCE(*ptr) }, __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:								\
+		while (!atomic_fcmpset_8((volatile u8 *)(ptr),		\
+	            __ret.u8, __new.u8[0]))				\
+			;						\
+		break;							\
+	case 2:								\
+		while (!atomic_fcmpset_16((volatile u16 *)(ptr),	\
+	            __ret.u16, __new.u16[0]))				\
+			;						\
+		break;							\
+	case 4:								\
+		while (!atomic_fcmpset_32((volatile u32 *)(ptr),	\
+	            __ret.u32, __new.u32[0]))				\
+			;						\
+		break;							\
+	case 8:								\
+		while (!atomic_fcmpset_64((volatile u64 *)(ptr),	\
+	            __ret.u64, __new.u64[0]))				\
+			;						\
+		break;							\
+	}								\
+	__ret.val;							\
 })
 
 #define	LINUX_ATOMIC_OP(op, c_op)				\