Deflake DBErrorHandlingFSTest.*WALWriteError (#10642)

Summary:
Example flake: https://app.circleci.com/pipelines/github/facebook/rocksdb/17660/workflows/7a891875-f07b-4a67-b204-eaa7ca9f9aa2/jobs/467496

The test could get stuck in out-of-space due to a callback executing `SetFilesystemActive(false /* active */)` after the test executed `SetFilesystemActive(true /* active */)`. This could happen because background info logging went through the SyncPoint callback "WritableFileWriter::Append:BeforePrepareWrite", probably unintentionally. The solution of this PR is to call `ClearAllCallBacks()` to wait for any such pending callbacks to drain before calling `SetFilesystemActive(true /* active */)`

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10642

Reviewed By: cbi42

Differential Revision: D39265381

Pulled By: ajkr

fbshipit-source-id: 9a2f4916ab19726c8fb4b3a3b590b1b9ed93de1b

db/error_handler_fs_test.cc

@@ -1308,6 +1308,10 @@ TEST_F(DBErrorHandlingFSTest, WALWriteError) {
     ASSERT_EQ(s, s.NoSpace());
   }
   SyncPoint::GetInstance()->DisableProcessing();
+  // `ClearAllCallBacks()` is needed in addition to `DisableProcessing()` to
+  // drain all callbacks. Otherwise, a pending callback in the background
+  // could re-disable `fault_fs_` after we enable it below.
+  SyncPoint::GetInstance()->ClearAllCallBacks();
   fault_fs_->SetFilesystemActive(true);
   ASSERT_EQ(listener->WaitForRecovery(5000000), true);
   for (auto i = 0; i < 199; ++i) {
@@ -1474,6 +1478,10 @@ TEST_F(DBErrorHandlingFSTest, MultiCFWALWriteError) {
     ASSERT_TRUE(s.IsNoSpace());
   }
   SyncPoint::GetInstance()->DisableProcessing();
+  // `ClearAllCallBacks()` is needed in addition to `DisableProcessing()` to
+  // drain all callbacks. Otherwise, a pending callback in the background
+  // could re-disable `fault_fs_` after we enable it below.
+  SyncPoint::GetInstance()->ClearAllCallBacks();
   fault_fs_->SetFilesystemActive(true);
   ASSERT_EQ(listener->WaitForRecovery(5000000), true);