Changeset 235d31d in mainline for kernel/generic/src/synch/waitq.c

Timestamp:

2014-12-22T17:47:40Z (9 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

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

Children:

8c7d5ad

Parents:

eae91e0 (diff), 759ea0d (diff)
Note: this is a merge changeset, the changes displayed below correspond to the merge itself.
Use the (diff) links above to see all the changes relative to each parent.

Message:

Merge the CHT pre-integration branch

This branch contains:

• the merge of lp:~adam-hraska+lp/helenos/rcu, which brings:

• a new preemptible kernel RCU variant called A-RCU,
• a preemptible variant of Podzimek's non-preemptible kernel RCU and
• a new variant of usersace RCU,
• a new concurrent hash table (CHT) implementation based on RCU,
• a deployment of CHT in kernel futex handling,
• a deployment of the userspace RCU in the implementation of upgradable futexes,

all described in Adam Hraska's master thesis named Read-Copy-Update
for HelenOS, defended in 2013 at MFF UK; furthemore, the branch
fixes two synchronization bugs in condvars and waitq, respectively:

• revid:adam.hraska+hos@gmail.com-20121116144921-3to9u1tn1sg07rg7
• revid:adam.hraska+hos@gmail.com-20121116173623-km7gwtqixwudpe66

• build fixes required to pass make check
• overhaul of ia64 and sparc64 trap handling, to allow exc_dispatch() to be used now when the kernel is more picky about CPU state accounting
• an important fix of the sparc64/sun4v preemptible trap handler
• various other fixes of issues discovered on non-x86 architectures

File:

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

kernel/generic/src/synch/waitq.c

@@ -57 +57 @@
 
 static void waitq_sleep_timed_out(void *);
+static void waitq_complete_wakeup(waitq_t *);
+
 
 /** Initialize wait queue
@@ -330 +332 @@
                 break;
         default:
+                /* 
+                 * Wait for a waitq_wakeup() or waitq_unsleep() to complete
+                 * before returning from waitq_sleep() to the caller. Otherwise
+                 * the caller might expect that the wait queue is no longer used 
+                 * and deallocate it (although the wakeup on a another cpu has 
+                 * not yet completed and is using the wait queue). 
+                 * 
+                 * Note that we have to do this for ESYNCH_OK_BLOCKED and
+                 * ESYNCH_INTERRUPTED, but not necessarily for ESYNCH_TIMEOUT
+                 * where the timeout handler stops using the waitq before waking 
+                 * us up. To be on the safe side, ensure the waitq is not in use 
+                 * anymore in this case as well.
+                 */
+                waitq_complete_wakeup(wq);
                 break;
         }
@@ -357 +373 @@
         } else {
                 if (PARAM_NON_BLOCKING(flags, usec)) {
-                        /* Return immediatelly instead of going to sleep */
+                        /* Return immediately instead of going to sleep */
                         return ESYNCH_WOULD_BLOCK;
                 }
@@ -442 +458 @@
         irq_spinlock_unlock(&wq->lock, true);
 }
+
+/** If there is a wakeup in progress actively waits for it to complete.
+ * 
+ * The function returns once the concurrently running waitq_wakeup()
+ * exits. It returns immediately if there are no concurrent wakeups 
+ * at the time.
+ * 
+ * Interrupts must be disabled.
+ * 
+ * Example usage:
+ * @code
+ * void callback(waitq *wq)
+ * {
+ *     // Do something and notify wait_for_completion() that we're done.
+ *     waitq_wakeup(wq);
+ * }
+ * void wait_for_completion(void) 
+ * {
+ *     waitq wg;
+ *     waitq_initialize(&wq);
+ *     // Run callback() in the background, pass it wq.
+ *     do_asynchronously(callback, &wq);
+ *     // Wait for callback() to complete its work.
+ *     waitq_sleep(&wq);
+ *     // callback() completed its work, but it may still be accessing 
+ *     // wq in waitq_wakeup(). Therefore it is not yet safe to return 
+ *     // from waitq_sleep() or it would clobber up our stack (where wq 
+ *     // is stored). waitq_sleep() ensures the wait queue is no longer
+ *     // in use by invoking waitq_complete_wakeup() internally.
+ *     
+ *     // waitq_sleep() returned, it is safe to free wq.
+ * }
+ * @endcode
+ * 
+ * @param wq  Pointer to a wait queue.
+ */
+static void waitq_complete_wakeup(waitq_t *wq)
+{
+        ASSERT(interrupts_disabled());
+        
+        irq_spinlock_lock(&wq->lock, false);
+        irq_spinlock_unlock(&wq->lock, false);
+}
+
 
 /** Internal SMP- and IRQ-unsafe version of waitq_wakeup()