On Thu, Nov 12, 2015 at 10:21:39AM -0800, Linus Torvalds wrote: > Now, the point of spin_unlock_wait() (and "spin_is_locked()") should > generally be that you have some external ordering guarantee that > guarantees that the lock has been taken. For example, for the IPC > semaphores, we do either one of: > > (a) get large lock, then - once you hold that lock - wait for each small lock > > or > > (b) get small lock, then - once you hold that lock - check that the > largo lock is unlocked > > and that's the case we should really worry about. The other uses of > spin_unlock_wait() should have similar "I have other reasons to know > I've seen that the lock was taken, or will never be taken after this > because XYZ".
I don't think this is true for the usage in do_exit(), we have no knowledge on if pi_lock is taken or not. We just want to make sure that _if_ it were taken, we wait until it is released. But I'm not sure where task_work_run() sits, at first reading it appears to also not be true -- there doesn't appear to be a reason we know a lock to be held. It does however appear true for the usage in completion_done(), where by having tested x->done, we know a pi_lock _was_ held. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
