Module: xenomai-forge
Branch: master
Commit: b8f5eac3a57ea4d2b485016aefff83aef0e5786f
URL:
http://git.xenomai.org/?p=xenomai-forge.git;a=commit;h=b8f5eac3a57ea4d2b485016aefff83aef0e5786f
Author: Philippe Gerum <r...@xenomai.org>
Date: Tue Nov 29 10:24:38 2011 +0100
copperplate/syncobj: sanitize detection of spurious wakeups
---
lib/copperplate/syncobj.c | 61 +++++++++++++++++++++++++++++---------------
1 files changed, 40 insertions(+), 21 deletions(-)
diff --git a/lib/copperplate/syncobj.c b/lib/copperplate/syncobj.c
index 249e9b2..7ed4ad8 100644
--- a/lib/copperplate/syncobj.c
+++ b/lib/copperplate/syncobj.c
@@ -207,11 +207,10 @@ void __syncobj_cleanup_wait(struct syncobj *sobj,
* saved in the syncstate struct since we are there precisely
* because the caller got cancelled.
*/
- if (holder_linked(&thobj->wait_link)) {
- list_remove(&thobj->wait_link);
- if (thobj->wait_status & SYNCOBJ_DRAINING)
- sobj->drain_count--;
- }
+ list_remove(&thobj->wait_link);
+ if (thobj->wait_status & SYNCOBJ_DRAINING)
+ sobj->drain_count--;
+
__RT(pthread_mutex_unlock(&sobj->lock));
}
@@ -223,9 +222,9 @@ int syncobj_pend(struct syncobj *sobj, const struct
timespec *timeout,
assert(current != NULL);
- current->wait_sobj = sobj;
current->wait_status = 0;
enqueue_waiter(sobj, current);
+ current->wait_sobj = sobj;
if (current->wait_hook)
current->wait_hook(sobj, SYNCOBJ_BLOCK);
@@ -250,18 +249,17 @@ int syncobj_pend(struct syncobj *sobj, const struct
timespec *timeout,
else
ret = wait_cond(¤t->wait_sync, &sobj->lock);
/* Check for spurious wake up. */
- } while (ret == 0 && holder_linked(¤t->wait_link));
+ } while (ret == 0 && current->wait_sobj);
pthread_setcancelstate(state, NULL);
if (current->wait_hook)
current->wait_hook(sobj, SYNCOBJ_RESUME);
- current->wait_sobj = NULL;
-
- if (ret)
- list_remove_init(¤t->wait_link);
- else if (current->wait_status & SYNCOBJ_DELETED) {
+ if (ret) {
+ current->wait_sobj = NULL;
+ list_remove(¤t->wait_link);
+ } else if (current->wait_status & SYNCOBJ_DELETED) {
syncobj_test_finalize(sobj, syns);
ret = EIDRM;
} else if (current->wait_status & SYNCOBJ_RELEASE_MASK) {
@@ -276,13 +274,14 @@ int syncobj_pend(struct syncobj *sobj, const struct
timespec *timeout,
void syncobj_requeue_waiter(struct syncobj *sobj, struct threadobj *thobj)
{
- list_remove_init(&thobj->wait_link);
+ list_remove(&thobj->wait_link);
enqueue_waiter(sobj, thobj);
}
void syncobj_wakeup_waiter(struct syncobj *sobj, struct threadobj *thobj)
{
- list_remove_init(&thobj->wait_link);
+ list_remove(&thobj->wait_link);
+ thobj->wait_sobj = NULL;
sobj->pend_count--;
signal_cond(&thobj->wait_sync);
}
@@ -295,6 +294,7 @@ struct threadobj *syncobj_post(struct syncobj *sobj)
return NULL;
thobj = list_pop_entry(&sobj->pend_list, struct threadobj, wait_link);
+ thobj->wait_sobj = NULL;
sobj->pend_count--;
signal_cond(&thobj->wait_sync);
@@ -332,12 +332,25 @@ int syncobj_wait_drain(struct syncobj *sobj, const struct
timespec *timeout,
int ret, state;
/*
- * XXX: The caller must check for spurious wakeups, in case
- * the drain condition became false again before it resumes.
+ * XXX: syncobj_wait_drain() behaves slightly differently than
+ * syncobj_pend(), in that we don't process spurious wakeups
+ * internally, leaving it to the caller. We do this because a
+ * drain sync is broadcast so we can't be 100% sure whether
+ * the wait condition actually disappeared for all waiters.
+ *
+ * (e.g. in case the drain signal notifies about a single
+ * resource being released, only one waiter will be satisfied,
+ * albeit all waiters will compete to get that resource - this
+ * means that all waiters but one will get a spurious wakeup).
+ *
+ * On the other hand, syncobj_pend() only unblocks on a
+ * directed wakeup signal to the waiting thread, so we can
+ * check whether such signal has existed prior to exiting the
+ * wait loop (i.e. testing current->wait_sobj for NULL).
*/
- current->wait_sobj = sobj;
current->wait_status = SYNCOBJ_DRAINING;
list_append(¤t->wait_link, &sobj->drain_list);
+ current->wait_sobj = sobj;
sobj->drain_count++;
pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, &state);
@@ -346,6 +359,10 @@ int syncobj_wait_drain(struct syncobj *sobj, const struct
timespec *timeout,
if (current->wait_hook)
current->wait_hook(sobj, SYNCOBJ_BLOCK);
+ /*
+ * XXX: The caller must check for spurious wakeups, in case
+ * the drain condition became false again before it resumes.
+ */
if (timeout)
ret = timedwait_cond(&sobj->post_sync,
&sobj->lock, timeout);
@@ -355,14 +372,14 @@ int syncobj_wait_drain(struct syncobj *sobj, const struct
timespec *timeout,
pthread_setcancelstate(state, NULL);
current->wait_status &= ~SYNCOBJ_DRAINING;
- if (current->wait_status == 0)
- list_remove_init(¤t->wait_link);
+ if (current->wait_status == 0) { /* not flushed? */
+ current->wait_sobj = NULL;
+ list_remove(¤t->wait_link);
+ }
if (current->wait_hook)
current->wait_hook(sobj, SYNCOBJ_RESUME);
- current->wait_sobj = NULL;
-
if (current->wait_status & SYNCOBJ_DELETED) {
syncobj_test_finalize(sobj, syns);
ret = EIDRM;
@@ -387,6 +404,7 @@ int syncobj_flush(struct syncobj *sobj, int reason)
thobj = list_pop_entry(&sobj->pend_list,
struct threadobj, wait_link);
thobj->wait_status |= reason;
+ thobj->wait_sobj = NULL;
signal_cond(&thobj->wait_sync);
sobj->release_count++;
}
@@ -396,6 +414,7 @@ int syncobj_flush(struct syncobj *sobj, int reason)
do {
thobj = list_pop_entry(&sobj->drain_list,
struct threadobj, wait_link);
+ thobj->wait_sobj = NULL;
thobj->wait_status |= reason;
} while (!list_empty(&sobj->drain_list));
sobj->release_count += sobj->drain_count;
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