Date: Sun, 11 Jul 1999 23:58:52 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: Peter Jeremy <jeremyp@gsmx07.alcatel.com.au> Cc: mike@ducky.net, freebsd-current@FreeBSD.ORG Subject: Re: "objtrm" problem probably found (was Re: Stuck in "objtrm") Message-ID: <199907120658.XAA66214@apollo.backplane.com> References: <99Jul12.085624est.40350@border.alcanet.com.au>
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:That said, it should be fairly simple to change Matt's new in-line
:assembler versions to insert LOCK prefixes when building an SMP
:kernel. (Although I don't know that this is necessary yet, given
:the `Big Giant Lock').
:
:There remains the problem of locating all the operations in the kernel
:that _should_ be atomic but aren't marked as such. Doug Rabson and
:the rest of the Alpha porting crew will have found a lot of these, but
:locating race conditions by waiting for them to occur is not the best
:solution.
:
:Peter
Here's the patch. Alan should be committing it (or something close to
it) soon. I did add the lock prefix, because I expect the SMP stuff will
eventually depend on the atomic macros actually being SMP-atomic.
It took a few iterations to get the __asm statement right :-)
This patch appears to fix the objtrm problem and may also fix other
potential VM races.
-Matt
Index: i386/include/atomic.h
===================================================================
RCS file: /home/ncvs/src/sys/i386/include/atomic.h,v
retrieving revision 1.1
diff -u -r1.1 atomic.h
--- atomic.h 1998/08/24 08:39:36 1.1
+++ atomic.h 1999/07/11 08:03:50
@@ -30,29 +30,131 @@
/*
* Various simple arithmetic on memory which is atomic in the presence
- * of interrupts.
+ * of interrupts. This code is now SMP safe as well.
*
- * Note: these versions are not SMP safe.
+ * The assembly is volatilized to demark potential before-and-after side
+ * effects if an interrupt or SMP collision were to occurs.
*/
-#define atomic_set_char(P, V) (*(u_char*)(P) |= (V))
-#define atomic_clear_char(P, V) (*(u_char*)(P) &= ~(V))
-#define atomic_add_char(P, V) (*(u_char*)(P) += (V))
-#define atomic_subtract_char(P, V) (*(u_char*)(P) -= (V))
-
-#define atomic_set_short(P, V) (*(u_short*)(P) |= (V))
-#define atomic_clear_short(P, V) (*(u_short*)(P) &= ~(V))
-#define atomic_add_short(P, V) (*(u_short*)(P) += (V))
-#define atomic_subtract_short(P, V) (*(u_short*)(P) -= (V))
-
-#define atomic_set_int(P, V) (*(u_int*)(P) |= (V))
-#define atomic_clear_int(P, V) (*(u_int*)(P) &= ~(V))
-#define atomic_add_int(P, V) (*(u_int*)(P) += (V))
-#define atomic_subtract_int(P, V) (*(u_int*)(P) -= (V))
-
-#define atomic_set_long(P, V) (*(u_long*)(P) |= (V))
-#define atomic_clear_long(P, V) (*(u_long*)(P) &= ~(V))
-#define atomic_add_long(P, V) (*(u_long*)(P) += (V))
-#define atomic_subtract_long(P, V) (*(u_long*)(P) -= (V))
+#define ATOMIC_ASM(type,op) \
+ __asm __volatile ("lock; " op : "=m" (*(type *)p) : "ir" (v), "0" (*(type *)p))
+
+static __inline void
+atomic_set_char(void *p, u_char v)
+{
+ ATOMIC_ASM(u_char, "orb %1,%0");
+}
+
+static __inline void
+atomic_clear_char(void *p, u_char v)
+{
+ v = ~v;
+ ATOMIC_ASM(u_char, "andb %1,%0");
+}
+
+static __inline void
+atomic_add_char(void *p, u_char v)
+{
+ ATOMIC_ASM(u_char, "addb %1,%0");
+}
+
+static __inline void
+atomic_subtract_char(void *p, u_char v)
+{
+ ATOMIC_ASM(u_char, "subb %1,%0");
+}
+
+static __inline void
+atomic_set_short(void *p, u_short v)
+{
+ ATOMIC_ASM(u_short, "orw %1,%0");
+}
+
+static __inline void
+atomic_clear_short(void *p, u_short v)
+{
+ v = ~v;
+ ATOMIC_ASM(u_short, "andw %1,%0");
+}
+
+static __inline void
+atomic_add_short(void *p, u_short v)
+{
+ ATOMIC_ASM(u_short, "addw %1,%0");
+}
+
+static __inline void
+atomic_subtract_short(void *p, u_short v)
+{
+ ATOMIC_ASM(u_short, "subw %1,%0");
+}
+
+
+static __inline void
+atomic_set_int(void *p, u_int v)
+{
+ ATOMIC_ASM(u_int, "orl %1,%0");
+}
+
+static __inline void
+atomic_clear_int(void *p, u_int v)
+{
+ v = ~v;
+ ATOMIC_ASM(u_int, "andl %1,%0");
+}
+
+static __inline void
+atomic_add_int(void *p, u_int v)
+{
+ ATOMIC_ASM(u_int, "addl %1,%0");
+}
+
+static __inline void
+atomic_subtract_int(void *p, u_int v)
+{
+ ATOMIC_ASM(u_int, "subl %1,%0");
+}
+
+
+static __inline void
+atomic_set_long(void *p, u_long v)
+{
+ ATOMIC_ASM(u_long, "orl %1,%0");
+}
+
+static __inline void
+atomic_clear_long(void *p, u_long v)
+{
+ v = ~v;
+ ATOMIC_ASM(u_long, "andl %1,%0");
+}
+
+static __inline void
+atomic_add_long(void *p, u_long v)
+{
+ ATOMIC_ASM(u_long, "addl %1,%0");
+}
+
+static __inline void
+atomic_subtract_long(void *p, u_long v)
+{
+ ATOMIC_ASM(u_long, "subl %1,%0");
+}
+
+#undef ATOMIC_ASM
+
+#ifndef I386_CPU
+
+static __inline int
+atomic_cmpex(volatile int *pint, int oldv, int newv)
+{
+ __asm __volatile ("/* %0 %1 */; lock; cmpxchgl %2,(%3)"
+ : "=a" (oldv)
+ : "a" (oldv), "r" (newv), "r" (pint)
+ );
+ return(oldv);
+}
+
+#endif
#endif /* ! _MACHINE_ATOMIC_H_ */
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