Changeset 20282ef3 in mainline for kernel/generic/src/ipc/sysipc.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/sysipc.c (modified) (1 diff)

kernel/generic/src/ipc/sysipc.c

@@ -175 +175 @@
                 return rc;
         } else {
+                ASSERT(answer->active);
+
+                /*
+                 * Mark the call as inactive to prevent _ipc_answer_free_call()
+                 * from attempting to remove the call from the active list
+                 * itself.
+                 */
+                answer->active = false;
+
+                /*
+                 * 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. 
+                 */
+                spinlock_lock(&answer->sender->active_calls_lock);
+                list_remove(&answer->ta_link);
+                spinlock_unlock(&answer->sender->active_calls_lock);
+
                 /*
                  * Hold the sender task so that it cannot suddenly disappear