[BUG] Fix deadlocks on disconnected secondary half (#17423)

platforms/chibios/drivers/serial.c

@@ -87,10 +87,7 @@ static THD_FUNCTION(Thread1, arg) {
     chRegSetThreadName("blinker");
     while (true) {
         palWaitLineTimeout(SOFT_SERIAL_PIN, TIME_INFINITE);
-
-        split_shared_memory_lock();
         interrupt_handler(NULL);
-        split_shared_memory_unlock();
     }
 }
 
@@ -155,6 +152,7 @@ static void __attribute__((noinline)) serial_write_byte(uint8_t data) {
 
 // interrupt handle to be used by the slave device
 void interrupt_handler(void *arg) {
+    split_shared_memory_lock_autounlock();
     chSysLockFromISR();
 
     sync_send();
@@ -212,6 +210,8 @@ void interrupt_handler(void *arg) {
 static inline bool initiate_transaction(uint8_t sstd_index) {
     if (sstd_index > NUM_TOTAL_TRANSACTIONS) return false;
 
+    split_shared_memory_lock_autounlock();
+
     split_transaction_desc_t *trans = &split_transaction_table[sstd_index];
 
     // TODO: remove extra delay between transactions
@@ -292,8 +292,5 @@ static inline bool initiate_transaction(uint8_t sstd_index) {
 //
 // this code is very time dependent, so we need to disable interrupts
 bool soft_serial_transaction(int sstd_index) {
-    split_shared_memory_lock();
-    bool result = initiate_transaction((uint8_t)sstd_index);
-    split_shared_memory_unlock();
-    return result;
+    return initiate_transaction((uint8_t)sstd_index);
 }

platforms/chibios/drivers/serial_protocol.c

@@ -22,13 +22,11 @@ static THD_FUNCTION(SlaveThread, arg) {
     chRegSetThreadName("split_protocol_tx_rx");
 
     while (true) {
-        split_shared_memory_lock();
         if (unlikely(!react_to_transaction())) {
             /* Clear the receive queue, to start with a clean slate.
              * Parts of failed transactions or spurious bytes could still be in it. */
             serial_transport_driver_clear();
         }
-        split_shared_memory_unlock();
     }
 }
 
@@ -64,6 +62,8 @@ static inline bool react_to_transaction(void) {
         return false;
     }
 
+    split_shared_memory_lock_autounlock();
+
     split_transaction_desc_t* transaction = &split_transaction_table[transaction_id];
 
     /* Send back the handshake which is XORed as a simple checksum,
@@ -102,9 +102,7 @@ static inline bool react_to_transaction(void) {
  * @return bool Indicates success of transaction.
  */
 bool soft_serial_transaction(int index) {
-    split_shared_memory_lock();
     bool result = initiate_transaction((uint8_t)index);
-    split_shared_memory_unlock();
 
     if (unlikely(!result)) {
         /* Clear the receive queue, to start with a clean slate.
@@ -125,6 +123,8 @@ static inline bool initiate_transaction(uint8_t transaction_id) {
         return false;
     }
 
+    split_shared_memory_lock_autounlock();
+
     split_transaction_desc_t* transaction = &split_transaction_table[transaction_id];
 
     /* Send transaction table index to the slave, which doubles as basic handshake token. */