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test_slru: Fix LWLock tranche allocation in EXEC_BACKEND builds.

author Nathan Bossart <nathan@postgresql.org>

Tue, 9 Sep 2025 19:09:36 +0000 (14:09 -0500)

committer Nathan Bossart <nathan@postgresql.org>

Tue, 9 Sep 2025 19:09:36 +0000 (14:09 -0500)

Currently, test_slru's shmem_startup_hook unconditionally generates
new LWLock tranche IDs. This is fine on non-EXEC_BACKEND builds,
where only the postmaster executes this hook, but on EXEC_BACKEND
builds, every backend executes it, too. To fix, only generate the
tranche IDs in the postmaster process by checking the
IsUnderPostmaster variable.

This is arguably a bug fix and could be back-patched, but since the
damage is limited to some extra unused tranche IDs in a test
module, I'm not going to bother.

Reported-by: Sami Imseih <samimseih@gmail.com>
Reviewed-by: Sami Imseih <samimseih@gmail.com>
Discussion: https://postgr.es/m/CAA5RZ0vaAuonaf12CeDddQJu5xKL%2B6xVyS%2B_q1%2BcH%3D33JXV82w%40mail.gmail.com

src/test/modules/test_slru/test_slru.c patch | blob | blame | history

diff --git a/src/test/modules/test_slru/test_slru.c b/src/test/modules/test_slru/test_slru.c

index 8c0367eeee424b21c92a4c01301506d0b53fc0b9..e963466aef1cdb758d835f61d957ed1ba721c572 100644 (file)

--- a/src/test/modules/test_slru/test_slru.c

+++ b/src/test/modules/test_slru/test_slru.c

@@ -219,8 +219,8 @@ test_slru_shmem_startup(void)

const bool long_segment_names = true;

const char slru_dir_name[] = "pg_test_slru";

- int test_tranche_id;

- int test_buffer_tranche_id;

+ int test_tranche_id = -1;

+ int test_buffer_tranche_id = -1;

if (prev_shmem_startup_hook)

prev_shmem_startup_hook();

@@ -231,10 +231,18 @@ test_slru_shmem_startup(void)

(void) MakePGDirectory(slru_dir_name);

- /* initialize the SLRU facility */

- test_tranche_id = LWLockNewTrancheId("test_slru_tranche");

- test_buffer_tranche_id = LWLockNewTrancheId("test_buffer_tranche");

+ /*

+ * Initialize the SLRU facility. In EXEC_BACKEND builds, the

+ * shmem_startup_hook is called in the postmaster and in each backend, but

+ * we only need to generate the LWLock tranches once. Note that these

+ * tranche ID variables are not used by SimpleLruInit() when

+ * IsUnderPostmaster is true.

+ */

+ if (!IsUnderPostmaster)

+ {

+ test_tranche_id = LWLockNewTrancheId("test_slru_tranche");

+ test_buffer_tranche_id = LWLockNewTrancheId("test_buffer_tranche");

+ }

TestSlruCtl->PagePrecedes = test_slru_page_precedes_logically;

SimpleLruInit(TestSlruCtl, "TestSLRU",

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