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SubjectRe: [PATCH v6 00/16] locking/lockdep: Add support for dynamic keys
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On Fri, 2019-01-11 at 13:48 +0100, Peter Zijlstra wrote:
> I spotted this new v6 in my inbox and have rebased to it.

Thanks!

> On Wed, Jan 09, 2019 at 01:01:48PM -0800, Bart Van Assche wrote:
>
> > The changes compared to v5 are:
> > - Modified zap_class() such that it doesn't try to free a list entry that
> > is already being freed.
>
> I however have a question on this; this seems wrong. Once a list entry
> is enqueued it should not be reachable anymore. If we can reach an entry
> after call_rcu() happened, we've got a problem.

Apparently I confused you - sorry that I was not more clear. What I meant is
that I changed a single if test into a loop. The graph lock is held while that
loop is being executed so the code below is serialized against the code called
from inside the RCU callback:

@@ -4574,8 +4563,9 @@ static void zap_class(struct pending_free *pf, struct lock
_class *class)
entry = list_entries + i;
if (entry->class != class && entry->links_to != class)
continue;
- if (__test_and_set_bit(i, pf->list_entries_being_freed))
+ if (list_entry_being_freed(i))
continue;
+ set_bit(i, pf->list_entries_being_freed);
nr_list_entries--;
list_del_rcu(&entry->entry);
}

Please let me know if you need more information.

Bart.

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