Make unified scheduler's new task code fallible

core/tests/unified_scheduler.rs

@@ -107,7 +107,9 @@ fn test_scheduler_waited_by_drop_bank_service() {
     // Delay transaction execution to ensure transaction execution happens after termintion has
     // been started
     let lock_to_stall = LOCK_TO_STALL.lock().unwrap();
-    pruned_bank.schedule_transaction_executions([(&tx, &0)].into_iter());
+    pruned_bank
+        .schedule_transaction_executions([(&tx, &0)].into_iter())
+        .unwrap();
     drop(pruned_bank);
     assert_eq!(pool_raw.pooled_scheduler_count(), 0);
     drop(lock_to_stall);

ledger/src/blockstore_processor.rs

@@ -338,11 +338,29 @@ fn process_batches(
             "process_batches()/schedule_batches_for_execution({} batches)",
             batches.len()
         );
-        // scheduling always succeeds here without being blocked on actual transaction executions.
-        // The transaction execution errors will be collected via the blocking fn called
-        // BankWithScheduler::wait_for_completed_scheduler(), if any.
-        schedule_batches_for_execution(bank, batches);
-        Ok(())
+        // Scheduling usually succeeds (immediately returns `Ok(())`) here without being blocked on
+        // the actual transaction executions.
+        //
+        // As an exception, this code path could propagate the transaction execution _errors of
+        // previously-scheduled transactions_ to notify the replay stage. Then, the replay stage
+        // will bail out the further processing of the malformed (possibly malicious) block
+        // immediately, not to waste any system resources. Note that this propagation is of early
+        // hints. Even if errors won't be propagated in this way, they are guaranteed to be
+        // propagated eventually via the blocking fn called
+        // BankWithScheduler::wait_for_completed_scheduler().
+        //
+        // To recite, the returned error is completely unrelated to the argument's `batches` at the
+        // hand. While being awkward, the _async_ unified scheduler is abusing this existing error
+        // propagation code path to the replay stage for compatibility and ease of integration,
+        // exploiting the fact that the replay stage doesn't care _which transaction the returned
+        // error is originating from_.
+        //
+        // In the future, more proper error propagation mechanism will be introduced once after we
+        // fully transition to the unified scheduler for the block verification. That one would be
+        // a push based one from the unified scheduler to the replay stage to eliminate the current
+        // overhead: 1 read lock per batch in
+        // `BankWithScheduler::schedule_transaction_executions()`.
+        schedule_batches_for_execution(bank, batches)
     } else {
         debug!(
             "process_batches()/rebatch_and_execute_batches({} batches)",
@@ -364,7 +382,7 @@ fn process_batches(
 fn schedule_batches_for_execution(
     bank: &BankWithScheduler,
     batches: &[TransactionBatchWithIndexes],
-) {
+) -> Result<()> {
     for TransactionBatchWithIndexes {
         batch,
         transaction_indexes,
@@ -375,8 +393,9 @@ fn schedule_batches_for_execution(
                 .sanitized_transactions()
                 .iter()
                 .zip(transaction_indexes.iter()),
-        );
+        )?;
     }
+    Ok(())
 }
 
 fn rebatch_transactions<'a>(
@@ -2139,7 +2158,8 @@ pub mod tests {
                 self, create_genesis_config_with_vote_accounts, ValidatorVoteKeypairs,
             },
             installed_scheduler_pool::{
-                MockInstalledScheduler, MockUninstalledScheduler, SchedulingContext,
+                MockInstalledScheduler, MockUninstalledScheduler, SchedulerAborted,
+                SchedulingContext,
             },
         },
         solana_sdk::{
@@ -4741,8 +4761,7 @@ pub mod tests {
         assert_eq!(batch3.transaction_indexes, vec![43, 44]);
     }
 
-    #[test]
-    fn test_schedule_batches_for_execution() {
+    fn do_test_schedule_batches_for_execution(should_succeed: bool) {
         solana_logger::setup();
         let dummy_leader_pubkey = solana_sdk::pubkey::new_rand();
         let GenesisConfigInfo {
@@ -4763,10 +4782,23 @@ pub mod tests {
             .times(1)
             .in_sequence(&mut seq.lock().unwrap())
             .return_const(context);
-        mocked_scheduler
-            .expect_schedule_execution()
-            .times(txs.len())
-            .returning(|_| ());
+        if should_succeed {
+            mocked_scheduler
+                .expect_schedule_execution()
+                .times(txs.len())
+                .returning(|(_, _)| Ok(()));
+        } else {
+            // mocked_scheduler isn't async; so short-circuiting behavior is quite visible in that
+            // .times(1) is called instead of .times(txs.len()), not like the succeeding case
+            mocked_scheduler
+                .expect_schedule_execution()
+                .times(1)
+                .returning(|(_, _)| Err(SchedulerAborted));
+            mocked_scheduler
+                .expect_recover_error_after_abort()
+                .times(1)
+                .returning(|| TransactionError::InsufficientFundsForFee);
+        }
         mocked_scheduler
             .expect_wait_for_termination()
             .with(mockall::predicate::eq(true))
@@ -4795,17 +4827,31 @@ pub mod tests {
         let replay_tx_thread_pool = create_thread_pool(1);
         let mut batch_execution_timing = BatchExecutionTiming::default();
         let ignored_prioritization_fee_cache = PrioritizationFeeCache::new(0u64);
-        assert!(process_batches(
+        let result = process_batches(
             &bank,
             &replay_tx_thread_pool,
             &[batch_with_indexes],
             None,
             None,
             &mut batch_execution_timing,
             None,
-            &ignored_prioritization_fee_cache
-        )
-        .is_ok());
+            &ignored_prioritization_fee_cache,
+        );
+        if should_succeed {
+            assert_matches!(result, Ok(()));
+        } else {
+            assert_matches!(result, Err(TransactionError::InsufficientFundsForFee));
+        }
+    }
+
+    #[test]
+    fn test_schedule_batches_for_execution_success() {
+        do_test_schedule_batches_for_execution(true);
+    }
+
+    #[test]
+    fn test_schedule_batches_for_execution_failure() {
+        do_test_schedule_batches_for_execution(false);
     }
 
     #[test]

runtime/src/installed_scheduler_pool.rs

@@ -27,7 +27,7 @@ use {
     solana_sdk::{
         hash::Hash,
         slot_history::Slot,
-        transaction::{Result, SanitizedTransaction},
+        transaction::{Result, SanitizedTransaction, TransactionError},
     },
     std::{
         fmt::Debug,
@@ -42,6 +42,10 @@ pub trait InstalledSchedulerPool: Send + Sync + Debug {
     fn take_scheduler(&self, context: SchedulingContext) -> InstalledSchedulerBox;
 }
 
+#[derive(Debug)]
+pub struct SchedulerAborted;
+pub type ScheduleResult = std::result::Result<(), SchedulerAborted>;
+
 #[cfg_attr(doc, aquamarine::aquamarine)]
 /// Schedules, executes, and commits transactions under encapsulated implementation
 ///
@@ -101,17 +105,51 @@ pub trait InstalledScheduler: Send + Sync + Debug + 'static {
     fn id(&self) -> SchedulerId;
     fn context(&self) -> &SchedulingContext;
 
-    // Calling this is illegal as soon as wait_for_termination is called.
+    /// Schedule transaction for execution.
+    ///
+    /// This non-blocking function will return immediately without waiting for actual execution.
+    ///
+    /// Calling this is illegal as soon as `wait_for_termination()` is called. It would result in
+    /// fatal logic error.
+    ///
+    /// Note that the returned result indicates whether the scheduler has been aborted due to a
+    /// previously-scheduled bad transaction, which terminates further block verification. So,
+    /// almost always, the returned error isn't due to the merely scheduling of the current
+    /// transaction itself. At this point, calling this does nothing anymore while it's still safe
+    /// to do. As soon as notified, callers are expected to stop processing upcoming transactions
+    /// of the same `SchedulingContext` (i.e. same block). Internally, the aborted scheduler will
+    /// be disposed cleanly, not repooled, after `wait_for_termination()` is called like
+    /// not-aborted schedulers.
+    ///
+    /// Caller can acquire the error by calling a separate function called
+    /// `recover_error_after_abort()`, which requires `&mut self`, instead of `&self`. This
+    /// separation and the convoluted returned value semantics explained above are intentional to
+    /// optimize the fast code-path of normal transaction scheduling to be multi-threaded at the
+    /// cost of far slower error code-path while giving implementors increased flexibility by
+    /// having &mut.
     fn schedule_execution<'a>(
         &'a self,
         transaction_with_index: &'a (&'a SanitizedTransaction, usize),
-    );
+    ) -> ScheduleResult;
+
+    /// Return the error which caused the scheduler to abort.
+    ///
+    /// Note that this must not be called until it's observed that `schedule_execution()` has
+    /// returned `Err(SchedulerAborted)`. Violating this will `panic!()`.
+    ///
+    /// That said, calling this multiple times is completely acceptable after the error observation
+    /// from `schedule_execution()`. While it's not guaranteed, the same `.clone()`-ed errors of
+    /// the first bad transaction are usually returned across invocations.
+    fn recover_error_after_abort(&mut self) -> TransactionError;
 
     /// Wait for a scheduler to terminate after processing.
     ///
     /// This function blocks the current thread while waiting for the scheduler to complete all of
     /// the executions for the scheduled transactions and to return the finalized
-    /// `ResultWithTimings`. Along with the result, this function also makes the scheduler itself
+    /// `ResultWithTimings`. This function still blocks for short period of time even in the case
+    /// of aborted schedulers to gracefully shutdown the scheduler (like thread joining).
+    ///
+    /// Along with the result being returned, this function also makes the scheduler itself
     /// uninstalled from the bank by transforming the consumed self.
     ///
     /// If no transaction is scheduled, the result and timing will be `Ok(())` and
@@ -286,11 +324,15 @@ impl BankWithScheduler {
         self.inner.scheduler.read().unwrap().is_some()
     }
 
+    /// Schedule the transaction as long as the scheduler hasn't been aborted.
+    ///
+    /// If the scheduler has been aborted, this doesn't schedule the transaction, instead just
+    /// return the error of prior scheduled transaction.
     // 'a is needed; anonymous_lifetime_in_impl_trait isn't stabilized yet...
     pub fn schedule_transaction_executions<'a>(
         &self,
         transactions_with_indexes: impl ExactSizeIterator<Item = (&'a SanitizedTransaction, &'a usize)>,
-    ) {
+    ) -> Result<()> {
         trace!(
             "schedule_transaction_executions(): {} txs",
             transactions_with_indexes.len()
@@ -300,8 +342,25 @@ impl BankWithScheduler {
         let scheduler = scheduler_guard.as_ref().unwrap();
 
         for (sanitized_transaction, &index) in transactions_with_indexes {
-            scheduler.schedule_execution(&(sanitized_transaction, index));
+            if scheduler
+                .schedule_execution(&(sanitized_transaction, index))
+                .is_err()
+            {
+                drop(scheduler_guard);
+                // This write lock isn't atomic with the above the read lock. So, another thread
+                // could have called .recover_error_after_abort() while we're literally stuck at
+                // the gaps of these locks (i.e. this comment in source code wise) under extreme
+                // race conditions. Thus, .recover_error_after_abort() is made idempotetnt for that
+                // consideration in mind.
+                //
+                // Lastly, this non-atomic nature is intentional for optimizing the fast code-path
+                let mut scheduler_guard = self.inner.scheduler.write().unwrap();
+                let scheduler = scheduler_guard.as_mut().unwrap();
+                return Err(scheduler.recover_error_after_abort());
+            }
         }
+
+        Ok(())
     }
 
     // take needless &mut only to communicate its semantic mutability to humans...
@@ -550,8 +609,7 @@ mod tests {
         assert_matches!(bank.wait_for_completed_scheduler(), Some(_));
     }
 
-    #[test]
-    fn test_schedule_executions() {
+    fn do_test_schedule_execution(should_succeed: bool) {
         solana_logger::setup();
 
         let GenesisConfigInfo {
@@ -570,14 +628,40 @@ mod tests {
             bank.clone(),
             [true].into_iter(),
             Some(|mocked: &mut MockInstalledScheduler| {
-                mocked
-                    .expect_schedule_execution()
-                    .times(1)
-                    .returning(|(_, _)| ());
+                if should_succeed {
+                    mocked
+                        .expect_schedule_execution()
+                        .times(1)
+                        .returning(|(_, _)| Ok(()));
+                } else {
+                    mocked
+                        .expect_schedule_execution()
+                        .times(1)
+                        .returning(|(_, _)| Err(SchedulerAborted));
+                    mocked
+                        .expect_recover_error_after_abort()
+                        .times(1)
+                        .returning(|| TransactionError::InsufficientFundsForFee);
+                }
             }),
         );
 
         let bank = BankWithScheduler::new(bank, Some(mocked_scheduler));
-        bank.schedule_transaction_executions([(&tx0, &0)].into_iter());
+        let result = bank.schedule_transaction_executions([(&tx0, &0)].into_iter());
+        if should_succeed {
+            assert_matches!(result, Ok(()));
+        } else {
+            assert_matches!(result, Err(TransactionError::InsufficientFundsForFee));
+        }
+    }
+
+    #[test]
+    fn test_schedule_execution_success() {
+        do_test_schedule_execution(true);
+    }
+
+    #[test]
+    fn test_schedule_execution_failure() {
+        do_test_schedule_execution(false);
     }
 }