diff options
Diffstat (limited to 'src/backend/utils/mmgr/mcxt.c')
| -rw-r--r-- | src/backend/utils/mmgr/mcxt.c | 116 |
1 files changed, 86 insertions, 30 deletions
diff --git a/src/backend/utils/mmgr/mcxt.c b/src/backend/utils/mmgr/mcxt.c index 15fa4d0a55e..47fd774c7d2 100644 --- a/src/backend/utils/mmgr/mcxt.c +++ b/src/backend/utils/mmgr/mcxt.c @@ -8,6 +8,23 @@ * context-type-specific operations via the function pointers in a * context's MemoryContextMethods struct. * + * A note about Valgrind support: when USE_VALGRIND is defined, we provide + * support for memory leak tracking at the allocation-unit level. Valgrind + * does leak detection by tracking allocated "chunks", which can be grouped + * into "pools". The "chunk" terminology is overloaded, since we use that + * word for our allocation units, and it's sometimes important to distinguish + * those from the Valgrind objects that describe them. To reduce confusion, + * let's use the terms "vchunk" and "vpool" for the Valgrind objects. + * + * We use a separate vpool for each memory context. The context-type-specific + * code is responsible for creating and deleting the vpools, and also for + * creating vchunks to cover its management data structures such as block + * headers. (There must be a vchunk that includes every pointer we want + * Valgrind to consider for leak-tracking purposes.) This module creates + * and deletes the vchunks that cover the caller-visible allocated chunks. + * However, the context-type-specific code must handle cleaning up those + * vchunks too during memory context reset operations. + * * * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California @@ -418,8 +435,6 @@ MemoryContextResetOnly(MemoryContext context) context->methods->reset(context); context->isReset = true; - VALGRIND_DESTROY_MEMPOOL(context); - VALGRIND_CREATE_MEMPOOL(context, 0, false); } } @@ -526,8 +541,6 @@ MemoryContextDeleteOnly(MemoryContext context) context->ident = NULL; context->methods->delete_context(context); - - VALGRIND_DESTROY_MEMPOOL(context); } /* @@ -560,9 +573,7 @@ MemoryContextDeleteChildren(MemoryContext context) * the specified context, since that means it will automatically be freed * when no longer needed. * - * There is no API for deregistering a callback once registered. If you - * want it to not do anything anymore, adjust the state pointed to by its - * "arg" to indicate that. + * Note that callers can assume this cannot fail. */ void MemoryContextRegisterResetCallback(MemoryContext context, @@ -578,6 +589,41 @@ MemoryContextRegisterResetCallback(MemoryContext context, } /* + * MemoryContextUnregisterResetCallback + * Undo the effects of MemoryContextRegisterResetCallback. + * + * This can be used if a callback's effects are no longer required + * at some point before the context has been reset/deleted. It is the + * caller's responsibility to pfree the callback struct (if needed). + * + * An assertion failure occurs if the callback was not registered. + * We could alternatively define that case as a no-op, but that seems too + * likely to mask programming errors such as passing the wrong context. + */ +void +MemoryContextUnregisterResetCallback(MemoryContext context, + MemoryContextCallback *cb) +{ + MemoryContextCallback *prev, + *cur; + + Assert(MemoryContextIsValid(context)); + + for (prev = NULL, cur = context->reset_cbs; cur != NULL; + prev = cur, cur = cur->next) + { + if (cur != cb) + continue; + if (prev) + prev->next = cur->next; + else + context->reset_cbs = cur->next; + return; + } + Assert(false); +} + +/* * MemoryContextCallResetCallbacks * Internal function to call all registered callbacks for context. */ @@ -1137,8 +1183,6 @@ MemoryContextCreate(MemoryContext node, node->nextchild = NULL; node->allowInCritSection = false; } - - VALGRIND_CREATE_MEMPOOL(node, 0, false); } /* @@ -1421,7 +1465,13 @@ MemoryContextAllocAligned(MemoryContext context, void *unaligned; void *aligned; - /* wouldn't make much sense to waste that much space */ + /* + * Restrict alignto to ensure that it can fit into the "value" field of + * the redirection MemoryChunk, and that the distance back to the start of + * the unaligned chunk will fit into the space available for that. This + * isn't a limitation in practice, since it wouldn't make much sense to + * waste that much space. + */ Assert(alignto < (128 * 1024 * 1024)); /* ensure alignto is a power of 2 */ @@ -1458,10 +1508,15 @@ MemoryContextAllocAligned(MemoryContext context, alloc_size += 1; #endif - /* perform the actual allocation */ - unaligned = MemoryContextAllocExtended(context, alloc_size, flags); + /* + * Perform the actual allocation, but do not pass down MCXT_ALLOC_ZERO. + * This ensures that wasted bytes beyond the aligned chunk do not become + * DEFINED. + */ + unaligned = MemoryContextAllocExtended(context, alloc_size, + flags & ~MCXT_ALLOC_ZERO); - /* set the aligned pointer */ + /* compute the aligned pointer */ aligned = (void *) TYPEALIGN(alignto, (char *) unaligned + sizeof(MemoryChunk)); @@ -1489,12 +1544,23 @@ MemoryContextAllocAligned(MemoryContext context, set_sentinel(aligned, size); #endif - /* Mark the bytes before the redirection header as noaccess */ - VALGRIND_MAKE_MEM_NOACCESS(unaligned, - (char *) alignedchunk - (char *) unaligned); + /* + * MemoryContextAllocExtended marked the whole unaligned chunk as a + * vchunk. Undo that, instead making just the aligned chunk be a vchunk. + * This prevents Valgrind from complaining that the vchunk is possibly + * leaked, since only pointers to the aligned chunk will exist. + * + * After these calls, the aligned chunk will be marked UNDEFINED, and all + * the rest of the unaligned chunk (the redirection chunk header, the + * padding bytes before it, and any wasted trailing bytes) will be marked + * NOACCESS, which is what we want. + */ + VALGRIND_MEMPOOL_FREE(context, unaligned); + VALGRIND_MEMPOOL_ALLOC(context, aligned, size); - /* Disallow access to the redirection chunk header. */ - VALGRIND_MAKE_MEM_NOACCESS(alignedchunk, sizeof(MemoryChunk)); + /* Now zero (and make DEFINED) just the aligned chunk, if requested */ + if ((flags & MCXT_ALLOC_ZERO) != 0) + MemSetAligned(aligned, 0, size); return aligned; } @@ -1528,16 +1594,12 @@ void pfree(void *pointer) { #ifdef USE_VALGRIND - MemoryContextMethodID method = GetMemoryChunkMethodID(pointer); MemoryContext context = GetMemoryChunkContext(pointer); #endif MCXT_METHOD(pointer, free_p) (pointer); -#ifdef USE_VALGRIND - if (method != MCTX_ALIGNED_REDIRECT_ID) - VALGRIND_MEMPOOL_FREE(context, pointer); -#endif + VALGRIND_MEMPOOL_FREE(context, pointer); } /* @@ -1547,9 +1609,6 @@ pfree(void *pointer) void * repalloc(void *pointer, Size size) { -#ifdef USE_VALGRIND - MemoryContextMethodID method = GetMemoryChunkMethodID(pointer); -#endif #if defined(USE_ASSERT_CHECKING) || defined(USE_VALGRIND) MemoryContext context = GetMemoryChunkContext(pointer); #endif @@ -1572,10 +1631,7 @@ repalloc(void *pointer, Size size) */ ret = MCXT_METHOD(pointer, realloc) (pointer, size, 0); -#ifdef USE_VALGRIND - if (method != MCTX_ALIGNED_REDIRECT_ID) - VALGRIND_MEMPOOL_CHANGE(context, pointer, ret, size); -#endif + VALGRIND_MEMPOOL_CHANGE(context, pointer, ret, size); return ret; } |