[NTOSKRNL]

Patch by Paolo Bonzini <bonzini [at] gnu [dot] org>
Fix implementation of ExInterlockedAddLargeStatistic
The old version wasn't really atomic.

See issue #6223 for more details.

svn path=/trunk/; revision=51748

reactos/ntoskrnl/ex/i386/fastinterlck_asm.S

@@ -4,6 +4,7 @@
  * FILE:            ntoskrnl/ex/i386/fastinterlck_asm.S
  * PURPOSE:         FASTCALL Interlocked Functions
  * PROGRAMMERS:     Alex Ionescu (alex@relsoft.net)
+ *                  Paolo Bonzini <bonzini [at] gnu [dot] org>
  */
 
 /* INCLUDES ******************************************************************/
@@ -31,26 +32,56 @@
  */
 PUBLIC @ExInterlockedAddLargeStatistic@8
 @ExInterlockedAddLargeStatistic@8:
+    push ebp
+    push ebx
+    mov  ebp, ecx
 
-#ifdef CONFIG_SMP
+Again:
-    /* Do the addition */
+    /* Load comparand in eax for cmpxchg */
-    lock add [ecx], edx
+    mov  eax, [ebp]
 
-    /* Check for carry bit and return */
+    /* Compute low word of the result in ebx */
-    jb .l1
+    mov  ebx, edx
+    add  ebx, eax
+
+    /* Carry needs cmpxchg8b */
+    jc   Slow
+
+    /* Fast path still needs to be atomic, so use cmpxchg and retry if it fails
+     * Hopefully it will still get through this path :) */
+    LOCK cmpxchg [ecx], ebx
+    jnz  Again
+
+    /* Thats it */
+    pop  ebx
+    pop  ebp
     ret
 
-.l1:
+Slow:
-    /* Add carry */
+    /* Save increment across cmpxchg8b */
-    lock adc dword ptr [ecx+4], 0
+    push edx
-#else
+
-    /* Do the addition and add the carry */
+    /* Finish loading comparand in edx:eax */
-    add dword ptr [ecx], edx
+    mov  edx, [ebp+4]
-    adc dword ptr [ecx+4], 0
+
-#endif
+    /* Result in ecx:ebx (we know there's carry) */
-    /* Return */
+    lea  ecx, [edx+1]
+
+    /* Do a full exchange */
+    LOCK cmpxchg8b [ebp]
+
+    /* restore increment */
+    pop  edx
+
+    /* Need to retry */
+    jnz  Again
+
+    /* Thats it */
+    pop  ebx
+    pop  ebp
     ret
 
+
 /*ULONG
  *FASTCALL
  *ExfInterlockedAddUlong(IN PULONG Addend,