Changeset 20282ef3 in mainline for kernel/generic/src/ipc/ipc.c

Timestamp:

2012-08-26T13:36:41Z (13 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

53af6e8c

Parents:

b1e6269

Message:

When answer_preprocess() wins the race for a call, let it also dequeue
the call from the sender's active list so that we have a real atomic
either-answered-or-forgotten behavior.

This change avoids the possibility that the race is won in
answer_preprocess(), but lost later in _ipc_answer_free_call(), which
would have the effect of skipping some of the necessary call_t cleanup.

File:

• kernel/generic/src/ipc/ipc.c (modified) (4 diffs)

kernel/generic/src/ipc/ipc.c

@@ -73 +73 @@
         memsetb(call, sizeof(*call), 0);
         spinlock_initialize(&call->forget_lock, "forget_lock");
+        call->active = false;
         call->forget = false;
         call->sender = TASK;
@@ -201 +202 @@
 
                 /*
-                 * Remove the call from the sender's active call list.
-                 * We enforce this locking order so that any potential
-                 * concurrently executing forget operation is forced to
-                 * release its active_calls_lock and lose the race to
-                 * forget this soon to be answered call. 
+                 * If the call is still active, i.e. it was answered
+                 * in a non-standard way, remove the call from the
+                 * sender's active call list.
                  */
-                spinlock_lock(&call->sender->active_calls_lock);
-                list_remove(&call->ta_link);
-                spinlock_unlock(&call->sender->active_calls_lock);
+                if (call->active) {
+                        spinlock_lock(&call->sender->active_calls_lock);
+                        list_remove(&call->ta_link);
+                        spinlock_unlock(&call->sender->active_calls_lock);
+                }
         }
         spinlock_unlock(&call->forget_lock);
@@ -291 +292 @@
         if (!(call->flags & IPC_CALL_FORWARDED)) {
                 atomic_inc(&phone->active_calls);
+
+                call->active = true;
 
                 spinlock_lock(&TASK->active_calls_lock);
@@ -594 +597 @@
         if (!spinlock_trylock(&call->forget_lock)) {
                 /*
-                 * Avoid deadlock and let _ipc_answer_free_call() win the race
-                 * to answer the first call on the list.
+                 * Avoid deadlock and let async_answer() or
+                 *  _ipc_answer_free_call() win the race to dequeue the first
+                 * call on the list.
                  */
                 spinlock_unlock(&TASK->active_calls_lock);