localbuf: Add Valgrind buffer access instrumentation

anarazel · nmisch · anarazel · commit 8ab4241b9f4f · 2025-04-07T15:20:30.000-04:00
This mirrors 1e0dfd1 (+ 46ef520), for temporary table buffers. This is mainly interesting right now because the AIO work currently triggers spurious valgrind errors, and the fix for that is cleaner if temp buffers behave the same as shared buffers. This requires one change beyond the annotations themselves, namely to pin local buffers while writing them out in FlushRelationBuffers(). Reviewed-by: Noah Misch <noah@leadboat.com> Co-authored-by: Noah Misch <noah@leadboat.com> Discussion: https://postgr.es/m/3pd4322mogfmdd5nln3zphdwhtmq3rzdldqjwb2sfqzcgs22lf@ok2gletdaoe6
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
@@ -4895,8 +4895,21 @@ FlushRelationBuffers(Relation rel)
 				errcallback.previous = error_context_stack;
 				error_context_stack = &errcallback;
 
+				/* Make sure we can handle the pin */
+				ReservePrivateRefCountEntry();
+				ResourceOwnerEnlarge(CurrentResourceOwner);
+
+				/*
+				 * Pin/upin mostly to make valgrind work, but it also seems
+				 * like the right thing to do.
+				 */
+				PinLocalBuffer(bufHdr, false);
+
+
 				FlushLocalBuffer(bufHdr, srel);
 
+				UnpinLocalBuffer(BufferDescriptorGetBuffer(bufHdr));
+
 				/* Pop the error context stack */
 				error_context_stack = errcallback.previous;
 			}
diff --git a/src/backend/storage/buffer/localbuf.c b/src/backend/storage/buffer/localbuf.c
@@ -23,6 +23,7 @@
 #include "storage/bufmgr.h"
 #include "storage/fd.h"
 #include "utils/guc_hooks.h"
+#include "utils/memdebug.h"
 #include "utils/memutils.h"
 #include "utils/resowner.h"
 
@@ -183,6 +184,8 @@ FlushLocalBuffer(BufferDesc *bufHdr, SMgrRelation reln)
 	instr_time	io_start;
 	Page		localpage = (char *) LocalBufHdrGetBlock(bufHdr);
 
+	Assert(LocalRefCount[-BufferDescriptorGetBuffer(bufHdr) - 1] > 0);
+
 	/*
 	 * Try to start an I/O operation.  There currently are no reasons for
 	 * StartLocalBufferIO to return false, so we raise an error in that case.
@@ -808,6 +811,15 @@ PinLocalBuffer(BufferDesc *buf_hdr, bool adjust_usagecount)
 			buf_state += BUF_USAGECOUNT_ONE;
 		}
 		pg_atomic_unlocked_write_u32(&buf_hdr->state, buf_state);
+
+		/*
+		 * See comment in PinBuffer().
+		 *
+		 * If the buffer isn't allocated yet, it'll be marked as defined in
+		 * GetLocalBufferStorage().
+		 */
+		if (LocalBufHdrGetBlock(buf_hdr) != NULL)
+			VALGRIND_MAKE_MEM_DEFINED(LocalBufHdrGetBlock(buf_hdr), BLCKSZ);
 	}
 	LocalRefCount[bufid]++;
 	ResourceOwnerRememberBuffer(CurrentResourceOwner,
@@ -843,6 +855,9 @@ UnpinLocalBufferNoOwner(Buffer buffer)
 		Assert(BUF_STATE_GET_REFCOUNT(buf_state) > 0);
 		buf_state -= BUF_REFCOUNT_ONE;
 		pg_atomic_unlocked_write_u32(&buf_hdr->state, buf_state);
+
+		/* see comment in UnpinBufferNoOwner */
+		VALGRIND_MAKE_MEM_NOACCESS(LocalBufHdrGetBlock(buf_hdr), BLCKSZ);
 	}
 }
 
@@ -923,6 +938,16 @@ GetLocalBufferStorage(void)
 	next_buf_in_block++;
 	total_bufs_allocated++;
 
+	/*
+	 * Caller's PinLocalBuffer() was too early for Valgrind updates, so do it
+	 * here.  The block is actually undefined, but we want consistency with
+	 * the regular case of not needing to allocate memory.  This is
+	 * specifically needed when method_io_uring.c fills the block, because
+	 * Valgrind doesn't recognize io_uring reads causing undefined memory to
+	 * become defined.
+	 */
+	VALGRIND_MAKE_MEM_DEFINED(this_buf, BLCKSZ);
+
 	return (Block) this_buf;
 }
 
