Re: 2.6.24-rc6: possible recursive locking detected

Oleg Nesterov
2008-01-07T17:21:14Z

On 01/05, Peter Zijlstra wrote:
>
> Since EP_MAX_POLLWAKE_NESTS < MAX_LOCKDEP_SUBCLASSES we could perhaps do
> something like:
>
> wake_up_nested(..., wake_nests);

I think this would be the most correct change. But I wonder if it is possible
to do something more generic (but otoh more stupid/hackish and less safe).

Consider this "just for illustration" patch,

--- t/kernel/lockdep.c 2007-11-09 12:57:31.000000000 +0300
+++ t/kernel/lockdep.c 2008-01-07 19:43:50.000000000 +0300
@@ -1266,10 +1266,13 @@ check_deadlock(struct task_struct *curr,
struct held_lock *prev;
int i;

- for (i = 0; i < curr->lockdep_depth; i++) {
+ for (i = curr->lockdep_depth; --i >= 0; ) {
prev = curr->held_locks + i;
if (prev->class != next->class)
continue;
+
+ if (prev->trylock == -1)
+ return 2;
/*
* Allow read-after-read recursion of the same
* lock class (i.e. read_lock(lock)+read_lock(lock)):
-------------------------------------------------------------------------

Now,

// trylock == -1
#define spin_mark_nested(l) \
lock_acquire(&(l)->dep_map, 0, -1, 0, 2, _THIS_IP_)
#define spin_unmark_nested(l) \
lock_release(&(l)->dep_map, 1, _THIS_IP_)

and ep_poll_safewake() can do:

/* Do really wake up now */
spin_mark_nested(&wq->lock);
wake_up(wq);
spin_unmark_nested(&wq->lock);

Possible?

Oleg.