Fix min_dynamic_shared_memory on Windows.

macdice · macdice · commit dab889d60bac · 2023-10-22T10:04:55.000+13:00
When min_dynamic_shared_memory is set above 0, we try to find space in a pre-allocated region of the main shared memory area instead of calling dsm_impl_XXX() routines to allocate more. The dsm_pin_segment() and dsm_unpin_segment() routines had a bug: they called dsm_impl_XXX() routines even for main region segments. Nobody noticed before now because those routines do nothing on Unix, but on Windows they'd fail while attempting to duplicate an invalid Windows HANDLE. Add the missing gating. Back-patch to 14, where commit 84b1c63 added this feature. Fixes pgsql-bugs bug #18165. Reported-by: Maxime Boyer <maxime.boyer@cra-arc.gc.ca> Tested-by: Alexander Lakhin <exclusion@gmail.com> Discussion: https://postgr.es/m/18165-bf4f525cea6e51de%40postgresql.org
diff --git a/src/backend/storage/ipc/dsm.c b/src/backend/storage/ipc/dsm.c
@@ -927,7 +927,7 @@ dsm_unpin_mapping(dsm_segment *seg)
 void
 dsm_pin_segment(dsm_segment *seg)
 {
-	void	   *handle;
+	void	   *handle = NULL;
 
 	/*
 	 * Bump reference count for this segment in shared memory. This will
@@ -938,7 +938,8 @@ dsm_pin_segment(dsm_segment *seg)
 	LWLockAcquire(DynamicSharedMemoryControlLock, LW_EXCLUSIVE);
 	if (dsm_control->item[seg->control_slot].pinned)
 		elog(ERROR, "cannot pin a segment that is already pinned");
-	dsm_impl_pin_segment(seg->handle, seg->impl_private, &handle);
+	if (!is_main_region_dsm_handle(seg->handle))
+		dsm_impl_pin_segment(seg->handle, seg->impl_private, &handle);
 	dsm_control->item[seg->control_slot].pinned = true;
 	dsm_control->item[seg->control_slot].refcnt++;
 	dsm_control->item[seg->control_slot].impl_private_pm_handle = handle;
@@ -995,8 +996,9 @@ dsm_unpin_segment(dsm_handle handle)
 	 * releasing the lock, because impl_private_pm_handle may get modified by
 	 * dsm_impl_unpin_segment.
 	 */
-	dsm_impl_unpin_segment(handle,
-						   &dsm_control->item[control_slot].impl_private_pm_handle);
+	if (!is_main_region_dsm_handle(handle))
+		dsm_impl_unpin_segment(handle,
+							   &dsm_control->item[control_slot].impl_private_pm_handle);
 
 	/* Note that 1 means no references (0 means unused slot). */
 	if (--dsm_control->item[control_slot].refcnt == 1)
