From 87761ebf290dfa853b2a3fb6b99f8c0da7fe998f Mon Sep 17 00:00:00 2001
From: Martin Konrad <konrad@frib.msu.edu>
Date: Mon, 3 Dec 2018 12:01:47 -0500
Subject: [PATCH] Prevent data race between resetHighWaterMark() and put()

---
 src/libCom/ring/epicsRingBytes.c   | 6 +++---
 src/libCom/ring/epicsRingPointer.h | 4 ++--
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/libCom/ring/epicsRingBytes.c b/src/libCom/ring/epicsRingBytes.c
index a9b13b990..ec9e5094d 100644
--- a/src/libCom/ring/epicsRingBytes.c
+++ b/src/libCom/ring/epicsRingBytes.c
@@ -121,7 +121,7 @@ epicsShareFunc int epicsShareAPI epicsRingBytesPut(
 {
     ringPvt *pring = (ringPvt *)id;
     int nextGet, nextPut, size;
-    int freeCount, copyCount, topCount, used;
+    int freeCount, copyCount, topCount, used, oldHWM;
 
     if (pring->lock) epicsSpinLock(pring->lock);
     nextGet = pring->nextGet;
@@ -162,8 +162,8 @@ epicsShareFunc int epicsShareAPI epicsRingBytesPut(
 
     used = nextPut - nextGet;
     if (used < 0) used += pring->size;
-    if (used > epicsAtomicGetIntT(&pring->highWaterMark)) {
-        epicsAtomicSetIntT(&pring->highWaterMark, used);
+    while(oldHWM = epicsAtomicGetIntT(&pring->highWaterMark), oldHWM < used) {
+        epicsAtomicCmpAndSwapIntT(&pring->highWaterMark, oldHWM, used);
     }
 
     if (pring->lock) epicsSpinUnlock(pring->lock);
diff --git a/src/libCom/ring/epicsRingPointer.h b/src/libCom/ring/epicsRingPointer.h
index b62923883..2b4f1b172 100644
--- a/src/libCom/ring/epicsRingPointer.h
+++ b/src/libCom/ring/epicsRingPointer.h
@@ -131,8 +131,8 @@ inline bool epicsRingPointer<T>::push(T *p)
     buffer[next] = p;
     nextPush = newNext;
     int used = getUsedNoLock();
-    if (used > epicsAtomicGetIntT(&highWaterMark)) {
-        epicsAtomicSetIntT(&highWaterMark, used);
+    while(int oldHWM = epicsAtomicGetIntT(&highWaterMark), oldHWM < used) {
+        epicsAtomicCmpAndSwapIntT(&highWaterMark, oldHWM, used);
     }
     if (lock) epicsSpinUnlock(lock);
     return(true);