Disable initdb cancellation (#6451)

## Problem

The initdb cancellation added in #5921 is not sufficient to reliably
abort the entire initdb process. Initdb also spawns children. The tests
added by #6310 (#6385) and #6436 now do initdb cancellations on a more
regular basis.

In #6385, I attempted to issue `killpg` (after giving it a new process
group ID) to kill not just the initdb but all its spawned subprocesses,
but this didn't work. Initdb doesn't take *that* long in the end either,
so we just wait until it concludes.

## Summary of changes

* revert initdb cancellation support added in #5921
* still return `Err(Cancelled)` upon cancellation, but this is just to
not have to remove the cancellation infrastructure
* fixes to the `test_tenant_delete_races_timeline_creation` test to make
it reliably pass

Fixes #6385

test_runner/fixtures/pageserver/utils.py

@@ -371,8 +371,24 @@ def tenant_delete_wait_completed(
     pageserver_http: PageserverHttpClient,
     tenant_id: TenantId,
     iterations: int,
+    ignore_errors: bool = False,
 ):
-    pageserver_http.tenant_delete(tenant_id=tenant_id)
+    if not ignore_errors:
+        pageserver_http.tenant_delete(tenant_id=tenant_id)
+    else:
+        interval = 0.5
+
+        def delete_request_sent():
+            try:
+                pageserver_http.tenant_delete(tenant_id=tenant_id)
+            except PageserverApiException as e:
+                log.debug(e)
+                if e.status_code == 404:
+                    return
+            except Exception as e:
+                log.debug(e)
+
+        wait_until(iterations, interval=interval, func=delete_request_sent)
     wait_tenant_status_404(pageserver_http, tenant_id=tenant_id, iterations=iterations)
 
 

test_runner/regress/test_tenant_delete.py

@@ -578,6 +578,9 @@ def test_tenant_delete_races_timeline_creation(
         ".*POST.*Cancelled request finished with an error: InternalServerError\\(.*ancelled"
     )
 
+    # This can occur sometimes.
+    CONFLICT_MESSAGE = ".*Precondition failed: Invalid state Stopping. Expected Active or Broken.*"
+
     env.pageserver.allowed_errors.extend(
         [
             # lucky race with stopping from flushing a layer we fail to schedule any uploads
@@ -586,6 +589,9 @@ def test_tenant_delete_races_timeline_creation(
             ".*POST.*/timeline.* request was dropped before completing",
             # Timeline creation runs into this error
             CANCELLED_ERROR,
+            # Timeline deletion can run into this error during deletion
+            CONFLICT_MESSAGE,
+            ".*tenant_delete_handler.*still waiting, taking longer than expected.*",
         ]
     )
 
@@ -621,7 +627,10 @@ def test_tenant_delete_races_timeline_creation(
     ps_http.configure_failpoints((DELETE_BEFORE_CLEANUP_FAILPOINT, "pause"))
 
     def tenant_delete():
-        ps_http.tenant_delete(tenant_id)
+        def tenant_delete_inner():
+            ps_http.tenant_delete(tenant_id)
+
+        wait_until(100, 0.5, tenant_delete_inner)
 
     Thread(target=tenant_delete).start()
 
@@ -638,10 +647,8 @@ def test_tenant_delete_races_timeline_creation(
     ps_http.configure_failpoints((BEFORE_INITDB_UPLOAD_FAILPOINT, "off"))
 
     iterations = poll_for_remote_storage_iterations(remote_storage_kind)
-    try:
-        tenant_delete_wait_completed(ps_http, tenant_id, iterations)
-    except PageserverApiException:
-        pass
+
+    tenant_delete_wait_completed(ps_http, tenant_id, iterations, ignore_errors=True)
 
     # Physical deletion should have happened
     assert_prefix_empty(