Remove volatile qualifiers from bufmgr.c and freelist.c

Prior to commit 0709b7ee, access to
variables within a spinlock-protected critical section had to be done
through a volatile pointer, but that should no longer be necessary.

Review by Andres Freund

src/backend/storage/buffer/freelist.c

@@ -98,9 +98,9 @@ typedef struct BufferAccessStrategyData
 
 
 /* Prototypes for internal functions */
-static volatile BufferDesc *GetBufferFromRing(BufferAccessStrategy strategy);
+static BufferDesc *GetBufferFromRing(BufferAccessStrategy strategy);
 static void AddBufferToRing(BufferAccessStrategy strategy,
-				volatile BufferDesc *buf);
+				BufferDesc *buf);
 
 /*
  * ClockSweepTick - Helper routine for StrategyGetBuffer()
@@ -179,10 +179,10 @@ ClockSweepTick(void)
  *	To ensure that no one else can pin the buffer before we do, we must
  *	return the buffer with the buffer header spinlock still held.
  */
-volatile BufferDesc *
+BufferDesc *
 StrategyGetBuffer(BufferAccessStrategy strategy)
 {
-	volatile BufferDesc *buf;
+	BufferDesc *buf;
 	int			bgwprocno;
 	int			trycounter;
 
@@ -338,7 +338,7 @@ StrategyGetBuffer(BufferAccessStrategy strategy)
  * StrategyFreeBuffer: put a buffer on the freelist
  */
 void
-StrategyFreeBuffer(volatile BufferDesc *buf)
+StrategyFreeBuffer(BufferDesc *buf)
 {
 	SpinLockAcquire(&StrategyControl->buffer_strategy_lock);
 
@@ -584,10 +584,10 @@ FreeAccessStrategy(BufferAccessStrategy strategy)
  *
  * The bufhdr spin lock is held on the returned buffer.
  */
-static volatile BufferDesc *
+static BufferDesc *
 GetBufferFromRing(BufferAccessStrategy strategy)
 {
-	volatile BufferDesc *buf;
+	BufferDesc *buf;
 	Buffer		bufnum;
 
 	/* Advance to next ring slot */
@@ -639,7 +639,7 @@ GetBufferFromRing(BufferAccessStrategy strategy)
  * is called with the spinlock held, it had better be quite cheap.
  */
 static void
-AddBufferToRing(BufferAccessStrategy strategy, volatile BufferDesc *buf)
+AddBufferToRing(BufferAccessStrategy strategy, BufferDesc *buf)
 {
 	strategy->buffers[strategy->current] = BufferDescriptorGetBuffer(buf);
 }
@@ -656,7 +656,7 @@ AddBufferToRing(BufferAccessStrategy strategy, volatile BufferDesc *buf)
  * if this buffer should be written and re-used.
  */
 bool
-StrategyRejectBuffer(BufferAccessStrategy strategy, volatile BufferDesc *buf)
+StrategyRejectBuffer(BufferAccessStrategy strategy, BufferDesc *buf)
 {
 	/* We only do this in bulkread mode */
 	if (strategy->btype != BAS_BULKREAD)

src/include/storage/buf_internals.h

@@ -194,11 +194,6 @@ typedef union BufferDescPadded
 /*
  * Macros for acquiring/releasing a shared buffer header's spinlock.
  * Do not apply these to local buffers!
- *
- * Note: as a general coding rule, if you are using these then you probably
- * need to be using a volatile-qualified pointer to the buffer header, to
- * ensure that the compiler doesn't rearrange accesses to the header to
- * occur before or after the spinlock is acquired/released.
  */
 #define LockBufHdr(bufHdr)		SpinLockAcquire(&(bufHdr)->buf_hdr_lock)
 #define UnlockBufHdr(bufHdr)	SpinLockRelease(&(bufHdr)->buf_hdr_lock)
@@ -216,10 +211,10 @@ extern BufferDesc *LocalBufferDescriptors;
  */
 
 /* freelist.c */
-extern volatile BufferDesc *StrategyGetBuffer(BufferAccessStrategy strategy);
-extern void StrategyFreeBuffer(volatile BufferDesc *buf);
+extern BufferDesc *StrategyGetBuffer(BufferAccessStrategy strategy);
+extern void StrategyFreeBuffer(BufferDesc *buf);
 extern bool StrategyRejectBuffer(BufferAccessStrategy strategy,
-					 volatile BufferDesc *buf);
+					 BufferDesc *buf);
 
 extern int	StrategySyncStart(uint32 *complete_passes, uint32 *num_buf_alloc);
 extern void StrategyNotifyBgWriter(int bgwprocno);