From 47c718792b885c2a06e32cf86f4caca69ce5cda4 Mon Sep 17 00:00:00 2001 From: Andres Freund Date: Mon, 8 Jun 2020 19:52:19 -0700 Subject: [PATCH] Avoid need for valgrind suppressions for pg_atomic_init_u64 on some platforms. Previously we used pg_atomic_write_64_impl inside pg_atomic_init_u64. That works correctly, but on platforms without 64bit single copy atomicity it could trigger spurious valgrind errors about uninitialized memory, because we use compare_and_swap for atomic writes on such platforms. I previously suppressed one instance of this problem (6c878edc1df), but as Tom reports that wasn't enough. As the atomic variable cannot yet be concurrently accessible during initialization, it seems better to have pg_atomic_init_64_impl set the value directly. Change pg_atomic_init_u32_impl for symmetry. Reported-By: Tom Lane Author: Andres Freund Discussion: https://postgr.es/m/1714601.1591503815@sss.pgh.pa.us Backpatch: 9.5- --- src/include/port/atomics/generic.h | 4 ++-- src/tools/valgrind.supp | 14 -------------- 2 files changed, 2 insertions(+), 16 deletions(-) diff --git a/src/include/port/atomics/generic.h b/src/include/port/atomics/generic.h index d3ba89a58f..d60a0d9e7f 100644 --- a/src/include/port/atomics/generic.h +++ b/src/include/port/atomics/generic.h @@ -160,7 +160,7 @@ pg_atomic_clear_flag_impl(volatile pg_atomic_flag *ptr) static inline void pg_atomic_init_u32_impl(volatile pg_atomic_uint32 *ptr, uint32 val_) { - pg_atomic_write_u32_impl(ptr, val_); + ptr->value = val_; } #endif @@ -330,7 +330,7 @@ pg_atomic_read_u64_impl(volatile pg_atomic_uint64 *ptr) static inline void pg_atomic_init_u64_impl(volatile pg_atomic_uint64 *ptr, uint64 val_) { - pg_atomic_write_u64_impl(ptr, val_); + ptr->value = val_; } #endif diff --git a/src/tools/valgrind.supp b/src/tools/valgrind.supp index acdb6206dd..e3a179d210 100644 --- a/src/tools/valgrind.supp +++ b/src/tools/valgrind.supp @@ -134,20 +134,6 @@ fun:IsBinaryCoercible } -# Atomic writes to 64bit atomic vars uses compare/exchange to -# guarantee atomic writes of 64bit variables. pg_atomic_write is used -# during initialization of the atomic variable; that leads to an -# initial read of the old, undefined, memory value. But that's just to -# make sure the swap works correctly. -{ - uninitialized_atomic_init_u64 - Memcheck:Cond - fun:pg_atomic_exchange_u64_impl - fun:pg_atomic_write_u64_impl - fun:pg_atomic_init_u64_impl -} - - # Python's allocator does some low-level tricks for efficiency. Those # can be disabled for better instrumentation; but few people testing # postgres will have such a build of python. So add broad