From d4a7e1886c1c34ab548f1a84374ba248faa2ae8a Mon Sep 17 00:00:00 2001 From: Michael Paquier Date: Tue, 26 May 2026 12:26:36 +0900 Subject: [PATCH] test_slru: Fix LWLock initialization for EXEC_BACKEND builds The LWLock used by this test module was defined as a process-local variable, which was broken under -DEXEC_BACKEND, each backend getting its own copy of the lock state. The shmem_startup_hook unconditionally called LWLockRegisterTranche() and LWLockInitialize(), which means that every backend would allocate a new tranche ID (which is still OK for this module) but reset the lock's atomic state (which was bad). This commit moves the LWLock to shared memory, so as it is initialized only once, similarly to pg_prewarm/autoprewarm.c. This change is only for REL_16_STABLE, per a report from buildfarm member gokiburi (the system has been upgraded recently, so perhaps it began failing due to some ALSR changes?). I have been able to reproduce the problem on the same host with -DEXEC_BACKEND, and checked that this commit addresses the issue. In v17 and v18, the test module wastes tranche IDs, which only impacts the visibility of the locks like in pg_stat_activity. The use of the SLRU bank locks ensures that the LWLock state is safe. On HEAD, the logic of the module is safer thanks to 38b602b0289f. Discussion: https://postgr.es/m/agr6-cIQ4EUA86Cs@paquier.xyz Backpatch-through: 16 --- src/test/modules/test_slru/test_slru.c | 35 +++++++++++++++++++------- src/tools/pgindent/typedefs.list | 1 + 2 files changed, 27 insertions(+), 9 deletions(-) diff --git a/src/test/modules/test_slru/test_slru.c b/src/test/modules/test_slru/test_slru.c index ae21444c476..2471be0c5b1 100644 --- a/src/test/modules/test_slru/test_slru.c +++ b/src/test/modules/test_slru/test_slru.c @@ -40,9 +40,16 @@ PG_FUNCTION_INFO_V1(test_slru_delete_all); /* Number of SLRU page slots */ #define NUM_TEST_BUFFERS 16 -/* SLRU control lock */ -LWLock TestSLRULock; -#define TestSLRULock (&TestSLRULock) +typedef struct TestSlruSharedState +{ + /* SLRU control lock */ + LWLock lock; +} TestSlruSharedState; + +/* Pointer to shared-memory state. */ +static TestSlruSharedState *test_slru_state = NULL; + +#define TestSLRULock (&test_slru_state->lock) static SlruCtlData TestSlruCtlData; #define TestSlruCtl (&TestSlruCtlData) @@ -202,6 +209,7 @@ test_slru_shmem_request(void) /* reserve shared memory for the test SLRU */ RequestAddinShmemSpace(SimpleLruShmemSize(NUM_TEST_BUFFERS, 0)); + RequestAddinShmemSpace(MAXALIGN(sizeof(TestSlruSharedState))); } static bool @@ -214,7 +222,7 @@ static void test_slru_shmem_startup(void) { const char slru_dir_name[] = "pg_test_slru"; - int test_tranche_id; + bool found; if (prev_shmem_startup_hook) prev_shmem_startup_hook(); @@ -225,15 +233,24 @@ test_slru_shmem_startup(void) */ (void) MakePGDirectory(slru_dir_name); - /* initialize the SLRU facility */ - test_tranche_id = LWLockNewTrancheId(); - LWLockRegisterTranche(test_tranche_id, "test_slru_tranche"); - LWLockInitialize(TestSLRULock, test_tranche_id); + LWLockAcquire(AddinShmemInitLock, LW_EXCLUSIVE); + test_slru_state = ShmemInitStruct("test_slru", + sizeof(TestSlruSharedState), + &found); + if (!found) + { + /* First time through ... */ + LWLockInitialize(&test_slru_state->lock, LWLockNewTrancheId()); + } + LWLockRelease(AddinShmemInitLock); + LWLockRegisterTranche(test_slru_state->lock.tranche, "test_slru"); + + /* initialize the SLRU facility */ TestSlruCtl->PagePrecedes = test_slru_page_precedes_logically; SimpleLruInit(TestSlruCtl, "TestSLRU", NUM_TEST_BUFFERS, 0, TestSLRULock, slru_dir_name, - test_tranche_id, SYNC_HANDLER_NONE); + test_slru_state->lock.tranche, SYNC_HANDLER_NONE); } void diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list index 8f7aab02bad..5ee0565a209 100644 --- a/src/tools/pgindent/typedefs.list +++ b/src/tools/pgindent/typedefs.list @@ -2784,6 +2784,7 @@ Tcl_Time TempNamespaceStatus TestDecodingData TestDecodingTxnData +TestSlruSharedState TestSpec TextFreq TextPositionState