Messages in this thread | | | Date | Wed, 4 Dec 2019 11:05:50 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH -tip] kprobes: Lock rcu_read_lock() while searching kprobe |
| |
* Paul E. McKenney <paulmck@kernel.org> wrote:
> > * This list-traversal primitive may safely run concurrently with > > * the _rcu list-mutation primitives such as hlist_add_head_rcu() > > * as long as the traversal is guarded by rcu_read_lock(). > > */ > > #define hlist_for_each_entry_rcu(pos, head, member, cond...) \ > > > > is actively harmful. Why is it there? > > For cases where common code might be invoked both from the reader > (with RCU protection) and from the updater (protected by some > lock). This common code can then use the optional argument to > hlist_for_each_entry_rcu() to truthfully tell lockdep that it might be > called with either form of protection in place. > > This also combines with the __rcu tag used to mark RCU-protected > pointers, in which case sparse complains when a non-RCU API is applied > to these pointers, to get back to your earlier question about use of > hlist_for_each_entry_rcu() within the update-side lock. > > But what are you seeing as actively harmful about all of this? > What should we be doing instead?
Yeah, so basically in the write-locked path hlist_for_each_entry() generates (slightly) more efficient code than hlist_for_each_entry_rcu(), correct?
Also, the principle of passing warning flags around is problematic - but I can see the point in this specific case.
Thanks,
Ingo
| |