From 07eeb9d109c057854b20707562ce517efa591761 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Wed, 12 Oct 2005 16:45:14 +0000 Subject: [PATCH] Do all accesses to shared buffer headers through volatile-qualified pointers, to ensure that compilers won't rearrange accesses to occur while we're not holding the buffer header spinlock. It's probably not necessary to mark volatile in every single place in bufmgr.c, but better safe than sorry. Per trouble report from Kevin Grittner. --- contrib/pg_buffercache/pg_buffercache_pages.c | 27 ++---- src/backend/storage/buffer/bufmgr.c | 89 ++++++++++--------- src/backend/storage/buffer/freelist.c | 8 +- src/include/storage/buf_internals.h | 11 ++- 4 files changed, 64 insertions(+), 71 deletions(-) diff --git a/contrib/pg_buffercache/pg_buffercache_pages.c b/contrib/pg_buffercache/pg_buffercache_pages.c index e55aff991d..e511c0df9a 100644 --- a/contrib/pg_buffercache/pg_buffercache_pages.c +++ b/contrib/pg_buffercache/pg_buffercache_pages.c @@ -3,7 +3,7 @@ * pg_buffercache_pages.c * display some contents of the buffer cache * - * $PostgreSQL: pgsql/contrib/pg_buffercache/pg_buffercache_pages.c,v 1.4 2005/05/31 00:07:47 tgl Exp $ + * $PostgreSQL: pgsql/contrib/pg_buffercache/pg_buffercache_pages.c,v 1.5 2005/10/12 16:45:13 tgl Exp $ *------------------------------------------------------------------------- */ #include "postgres.h" @@ -72,10 +72,8 @@ pg_buffercache_pages(PG_FUNCTION_ARGS) if (SRF_IS_FIRSTCALL()) { - RelFileNode rnode; uint32 i; - BufferDesc *bufHdr; - + volatile BufferDesc *bufHdr; funcctx = SRF_FIRSTCALL_INIT(); @@ -136,35 +134,24 @@ pg_buffercache_pages(PG_FUNCTION_ARGS) /* Lock each buffer header before inspecting. */ LockBufHdr(bufHdr); - rnode = bufHdr->tag.rnode; - fctx->record[i].bufferid = BufferDescriptorGetBuffer(bufHdr); - fctx->record[i].relfilenode = rnode.relNode; - fctx->record[i].reltablespace = rnode.spcNode; - fctx->record[i].reldatabase = rnode.dbNode; + fctx->record[i].relfilenode = bufHdr->tag.rnode.relNode; + fctx->record[i].reltablespace = bufHdr->tag.rnode.spcNode; + fctx->record[i].reldatabase = bufHdr->tag.rnode.dbNode; fctx->record[i].blocknum = bufHdr->tag.blockNum; - if ( bufHdr->flags & BM_DIRTY) - { + if (bufHdr->flags & BM_DIRTY) fctx->record[i].isdirty = true; - } else - { fctx->record[i].isdirty = false; - } /* Note if the buffer is valid, and has storage created */ - if ( (bufHdr->flags & BM_VALID) && (bufHdr->flags & BM_TAG_VALID)) - { + if ((bufHdr->flags & BM_VALID) && (bufHdr->flags & BM_TAG_VALID)) fctx->record[i].isvalid = true; - } else - { fctx->record[i].isvalid = false; - } UnlockBufHdr(bufHdr); - } /* Release Buffer map. */ diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index 51b3f56c81..fb3efcbca9 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -8,7 +8,7 @@ * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.195 2005/08/12 23:13:54 momjian Exp $ + * $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.196 2005/10/12 16:45:13 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -76,24 +76,24 @@ long NDirectFileWrite; /* e.g., I/O in psort and hashjoin. */ /* local state for StartBufferIO and related functions */ -static BufferDesc *InProgressBuf = NULL; +static volatile BufferDesc *InProgressBuf = NULL; static bool IsForInput; /* local state for LockBufferForCleanup */ -static BufferDesc *PinCountWaitBuf = NULL; +static volatile BufferDesc *PinCountWaitBuf = NULL; -static bool PinBuffer(BufferDesc *buf); -static void PinBuffer_Locked(BufferDesc *buf); -static void UnpinBuffer(BufferDesc *buf, bool fixOwner, bool trashOK); +static bool PinBuffer(volatile BufferDesc *buf); +static void PinBuffer_Locked(volatile BufferDesc *buf); +static void UnpinBuffer(volatile BufferDesc *buf, bool fixOwner, bool trashOK); static bool SyncOneBuffer(int buf_id, bool skip_pinned); -static void WaitIO(BufferDesc *buf); -static bool StartBufferIO(BufferDesc *buf, bool forInput); -static void TerminateBufferIO(BufferDesc *buf, bool clear_dirty, +static void WaitIO(volatile BufferDesc *buf); +static bool StartBufferIO(volatile BufferDesc *buf, bool forInput); +static void TerminateBufferIO(volatile BufferDesc *buf, bool clear_dirty, int set_flag_bits); static void buffer_write_error_callback(void *arg); -static BufferDesc *BufferAlloc(Relation reln, BlockNumber blockNum, +static volatile BufferDesc *BufferAlloc(Relation reln, BlockNumber blockNum, bool *foundPtr); -static void FlushBuffer(BufferDesc *buf, SMgrRelation reln); +static void FlushBuffer(volatile BufferDesc *buf, SMgrRelation reln); static void AtProcExit_Buffers(int code, Datum arg); static void write_buffer(Buffer buffer, bool unpin); @@ -116,7 +116,7 @@ static void write_buffer(Buffer buffer, bool unpin); Buffer ReadBuffer(Relation reln, BlockNumber blockNum) { - BufferDesc *bufHdr; + volatile BufferDesc *bufHdr; Block bufBlock; bool found; bool isExtend; @@ -255,7 +255,7 @@ ReadBuffer(Relation reln, BlockNumber blockNum) * * No locks are held either at entry or exit. */ -static BufferDesc * +static volatile BufferDesc * BufferAlloc(Relation reln, BlockNumber blockNum, bool *foundPtr) @@ -264,7 +264,7 @@ BufferAlloc(Relation reln, BufferTag oldTag; BufFlags oldFlags; int buf_id; - BufferDesc *buf; + volatile BufferDesc *buf; bool valid; /* create a tag so we can lookup the buffer */ @@ -512,7 +512,7 @@ BufferAlloc(Relation reln, * to acquire the necessary locks; if so, don't mess it up. */ static void -InvalidateBuffer(BufferDesc *buf) +InvalidateBuffer(volatile BufferDesc *buf) { BufferTag oldTag; BufFlags oldFlags; @@ -602,7 +602,7 @@ retry: static void write_buffer(Buffer buffer, bool unpin) { - BufferDesc *bufHdr; + volatile BufferDesc *bufHdr; if (!BufferIsValid(buffer)) elog(ERROR, "bad buffer id: %d", buffer); @@ -679,7 +679,7 @@ ReleaseAndReadBuffer(Buffer buffer, Relation relation, BlockNumber blockNum) { - BufferDesc *bufHdr; + volatile BufferDesc *bufHdr; if (BufferIsValid(buffer)) { @@ -722,7 +722,7 @@ ReleaseAndReadBuffer(Buffer buffer, * some callers to avoid an extra spinlock cycle. */ static bool -PinBuffer(BufferDesc *buf) +PinBuffer(volatile BufferDesc *buf) { int b = buf->buf_id; bool result; @@ -760,7 +760,7 @@ PinBuffer(BufferDesc *buf) * its state can change under us. */ static void -PinBuffer_Locked(BufferDesc *buf) +PinBuffer_Locked(volatile BufferDesc *buf) { int b = buf->buf_id; @@ -787,7 +787,7 @@ PinBuffer_Locked(BufferDesc *buf) * used recently, and trashOK is true, send the buffer to the freelist. */ static void -UnpinBuffer(BufferDesc *buf, bool fixOwner, bool trashOK) +UnpinBuffer(volatile BufferDesc *buf, bool fixOwner, bool trashOK) { int b = buf->buf_id; @@ -967,7 +967,7 @@ BgBufferSync(void) static bool SyncOneBuffer(int buf_id, bool skip_pinned) { - BufferDesc *bufHdr = &BufferDescriptors[buf_id]; + volatile BufferDesc *bufHdr = &BufferDescriptors[buf_id]; /* * Check whether buffer needs writing. @@ -1114,7 +1114,7 @@ AtProcExit_Buffers(int code, Datum arg) { if (PrivateRefCount[i] != 0) { - BufferDesc *buf = &(BufferDescriptors[i]); + volatile BufferDesc *buf = &(BufferDescriptors[i]); /* * We don't worry about updating ResourceOwner; if we even got @@ -1136,7 +1136,7 @@ AtProcExit_Buffers(int code, Datum arg) void PrintBufferLeakWarning(Buffer buffer) { - BufferDesc *buf; + volatile BufferDesc *buf; int32 loccount; Assert(BufferIsValid(buffer)); @@ -1199,7 +1199,7 @@ BufmgrCommit(void) BlockNumber BufferGetBlockNumber(Buffer buffer) { - BufferDesc *bufHdr; + volatile BufferDesc *bufHdr; Assert(BufferIsPinned(buffer)); @@ -1222,7 +1222,7 @@ BufferGetBlockNumber(Buffer buffer) RelFileNode BufferGetFileNode(Buffer buffer) { - BufferDesc *bufHdr; + volatile BufferDesc *bufHdr; if (BufferIsLocal(buffer)) bufHdr = &(LocalBufferDescriptors[-buffer - 1]); @@ -1252,7 +1252,7 @@ BufferGetFileNode(Buffer buffer) * as the second parameter. If not, pass NULL. */ static void -FlushBuffer(BufferDesc *buf, SMgrRelation reln) +FlushBuffer(volatile BufferDesc *buf, SMgrRelation reln) { XLogRecPtr recptr; ErrorContextCallback errcontext; @@ -1267,7 +1267,7 @@ FlushBuffer(BufferDesc *buf, SMgrRelation reln) /* Setup error traceback support for ereport() */ errcontext.callback = buffer_write_error_callback; - errcontext.arg = buf; + errcontext.arg = (void *) buf; errcontext.previous = error_context_stack; error_context_stack = &errcontext; @@ -1375,7 +1375,7 @@ DropRelFileNodeBuffers(RelFileNode rnode, bool istemp, BlockNumber firstDelBlock) { int i; - BufferDesc *bufHdr; + volatile BufferDesc *bufHdr; if (istemp) { @@ -1427,7 +1427,7 @@ void DropBuffers(Oid dbid) { int i; - BufferDesc *bufHdr; + volatile BufferDesc *bufHdr; /* * We needn't consider local buffers, since by assumption the target @@ -1457,7 +1457,7 @@ void PrintBufferDescs(void) { int i; - BufferDesc *buf = BufferDescriptors; + volatile BufferDesc *buf = BufferDescriptors; for (i = 0; i < NBuffers; ++i, ++buf) { @@ -1479,7 +1479,7 @@ void PrintPinnedBufs(void) { int i; - BufferDesc *buf = BufferDescriptors; + volatile BufferDesc *buf = BufferDescriptors; for (i = 0; i < NBuffers; ++i, ++buf) { @@ -1522,7 +1522,7 @@ void FlushRelationBuffers(Relation rel) { int i; - BufferDesc *bufHdr; + volatile BufferDesc *bufHdr; /* Open rel at the smgr level if not already done */ RelationOpenSmgr(rel); @@ -1539,7 +1539,7 @@ FlushRelationBuffers(Relation rel) /* Setup error traceback support for ereport() */ errcontext.callback = buffer_write_error_callback; - errcontext.arg = bufHdr; + errcontext.arg = (void *) bufHdr; errcontext.previous = error_context_stack; error_context_stack = &errcontext; @@ -1586,7 +1586,7 @@ FlushRelationBuffers(Relation rel) void ReleaseBuffer(Buffer buffer) { - BufferDesc *bufHdr; + volatile BufferDesc *bufHdr; if (!BufferIsValid(buffer)) elog(ERROR, "bad buffer id: %d", buffer); @@ -1657,7 +1657,7 @@ IncrBufferRefCount(Buffer buffer) void SetBufferCommitInfoNeedsSave(Buffer buffer) { - BufferDesc *bufHdr; + volatile BufferDesc *bufHdr; if (!BufferIsValid(buffer)) elog(ERROR, "bad buffer id: %d", buffer); @@ -1694,7 +1694,7 @@ SetBufferCommitInfoNeedsSave(Buffer buffer) void UnlockBuffers(void) { - BufferDesc *buf = PinCountWaitBuf; + volatile BufferDesc *buf = PinCountWaitBuf; if (buf) { @@ -1727,7 +1727,7 @@ UnlockBuffers(void) void LockBuffer(Buffer buffer, int mode) { - BufferDesc *buf; + volatile BufferDesc *buf; Assert(BufferIsValid(buffer)); if (BufferIsLocal(buffer)) @@ -1765,7 +1765,7 @@ LockBuffer(Buffer buffer, int mode) bool ConditionalLockBuffer(Buffer buffer) { - BufferDesc *buf; + volatile BufferDesc *buf; Assert(BufferIsValid(buffer)); if (BufferIsLocal(buffer)) @@ -1809,7 +1809,7 @@ ConditionalLockBuffer(Buffer buffer) void LockBufferForCleanup(Buffer buffer) { - BufferDesc *bufHdr; + volatile BufferDesc *bufHdr; Assert(BufferIsValid(buffer)); Assert(PinCountWaitBuf == NULL); @@ -1875,7 +1875,7 @@ LockBufferForCleanup(Buffer buffer) * WaitIO -- Block until the IO_IN_PROGRESS flag on 'buf' is cleared. */ static void -WaitIO(BufferDesc *buf) +WaitIO(volatile BufferDesc *buf) { /* * Changed to wait until there's no IO - Inoue 01/13/2000 @@ -1922,7 +1922,7 @@ WaitIO(BufferDesc *buf) * FALSE if someone else already did the work. */ static bool -StartBufferIO(BufferDesc *buf, bool forInput) +StartBufferIO(volatile BufferDesc *buf, bool forInput) { Assert(!InProgressBuf); @@ -1989,7 +1989,8 @@ StartBufferIO(BufferDesc *buf, bool forInput) * be 0, or BM_VALID if we just finished reading in the page. */ static void -TerminateBufferIO(BufferDesc *buf, bool clear_dirty, int set_flag_bits) +TerminateBufferIO(volatile BufferDesc *buf, bool clear_dirty, + int set_flag_bits) { Assert(buf == InProgressBuf); @@ -2021,7 +2022,7 @@ TerminateBufferIO(BufferDesc *buf, bool clear_dirty, int set_flag_bits) void AbortBufferIO(void) { - BufferDesc *buf = InProgressBuf; + volatile BufferDesc *buf = InProgressBuf; if (buf) { @@ -2075,7 +2076,7 @@ AbortBufferIO(void) static void buffer_write_error_callback(void *arg) { - BufferDesc *bufHdr = (BufferDesc *) arg; + volatile BufferDesc *bufHdr = (volatile BufferDesc *) arg; /* Buffer is pinned, so we can read the tag without locking the spinlock */ if (bufHdr != NULL) diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c index 906165638b..4739512ad3 100644 --- a/src/backend/storage/buffer/freelist.c +++ b/src/backend/storage/buffer/freelist.c @@ -9,7 +9,7 @@ * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/storage/buffer/freelist.c,v 1.52 2005/08/20 23:26:17 tgl Exp $ + * $PostgreSQL: pgsql/src/backend/storage/buffer/freelist.c,v 1.53 2005/10/12 16:45:13 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -55,10 +55,10 @@ bool strategy_hint_vacuum = false; * means that we return with the BufFreelistLock still held, as well; * the caller must release that lock once the spinlock is dropped. */ -BufferDesc * +volatile BufferDesc * StrategyGetBuffer(void) { - BufferDesc *buf; + volatile BufferDesc *buf; int trycounter; LWLockAcquire(BufFreelistLock, LW_EXCLUSIVE); @@ -138,7 +138,7 @@ StrategyGetBuffer(void) * quickly the buffer is reused. */ void -StrategyFreeBuffer(BufferDesc *buf, bool at_head) +StrategyFreeBuffer(volatile BufferDesc *buf, bool at_head) { LWLockAcquire(BufFreelistLock, LW_EXCLUSIVE); diff --git a/src/include/storage/buf_internals.h b/src/include/storage/buf_internals.h index 6e083be21b..e75f24a6ce 100644 --- a/src/include/storage/buf_internals.h +++ b/src/include/storage/buf_internals.h @@ -8,7 +8,7 @@ * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * - * $PostgreSQL: pgsql/src/include/storage/buf_internals.h,v 1.79 2005/08/20 23:26:33 tgl Exp $ + * $PostgreSQL: pgsql/src/include/storage/buf_internals.h,v 1.80 2005/10/12 16:45:14 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -145,6 +145,11 @@ typedef struct sbufdesc * NoHoldoff cases may be used when we know that we hold some LWLock * and therefore interrupts are already held off. Do not apply these * to local buffers! + * + * Note: as a general coding rule, if you are using these then you probably + * want 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) @@ -179,8 +184,8 @@ extern long int LocalBufferFlushCount; */ /* freelist.c */ -extern BufferDesc *StrategyGetBuffer(void); -extern void StrategyFreeBuffer(BufferDesc *buf, bool at_head); +extern volatile BufferDesc *StrategyGetBuffer(void); +extern void StrategyFreeBuffer(volatile BufferDesc *buf, bool at_head); extern int StrategySyncStart(void); extern Size StrategyShmemSize(void); extern void StrategyInitialize(bool init); -- 2.49.0