Laurent Morichetti
6f78083f2a
When acquiring the reader's lock (sem_sync()...sem_release()), it is
possible for a writer to squeeze by if the reader goes into sync_wait().
The writer could re-acquire the entry.sync between entry.sem > 0 and
entry.sync = 0.
void sync_wait(uint32_t id) {
sem_decrement(id);
while (entry(id).sync.load()) {}
// <--- HERE
sem_increment(id);
}
This could result in both the reader and the writer accessing
{ callback, arg } at the same time, and the reader could read
inconsistent data, for example: { new callback, old arg }.
The solution is to re-test entry.sync when returning from sync_wait():
void sem_sync(uint32_t id) {
sem_increment(id);
- if (entry(id).sync.load() == true) sync_wait(id);
+ while (entry(id).sync.load() == true) sync_wait(id);
}
Change-Id: I22f74f4cb9a5f027aac8aa4ed3e633acc19df4b8