Commit-ID: efd88b02bb9e6b8b73a20ea611e5d07ed6d4af34 Gitweb: https://git.kernel.org/tip/efd88b02bb9e6b8b73a20ea611e5d07ed6d4af34 Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> AuthorDate: Thu, 19 Oct 2017 14:52:41 -0700 Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> CommitDate: Mon, 11 Dec 2017 09:17:39 -0800 rcu: Add comment giving debug strategy for double call_rcu() The following statement has for some reason proven non-intuitive: WARN_ON_ONCE(rcu_segcblist_empty(&rdp->cblist) != (count == 0)); This commit therefore adds a comment that states that this warning usually triggers in response to a double call_rcu(), which is sort of like a double free. The comment also suggests building with CONFIG_DEBUG_OBJECTS_RCU_HEAD=y to track down the double call_rcu(). Reported-by: David Howells <dhowells@xxxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> --- kernel/rcu/tree.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index f9c0ca2..1bdc048 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2789,6 +2789,11 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp) rdp->n_force_qs_snap = rsp->n_force_qs; } else if (count < rdp->qlen_last_fqs_check - qhimark) rdp->qlen_last_fqs_check = count; + + /* + * The following usually indicates a double call_rcu(). To track + * this down, try building with CONFIG_DEBUG_OBJECTS_RCU_HEAD=y. + */ WARN_ON_ONCE(rcu_segcblist_empty(&rdp->cblist) != (count == 0)); local_irq_restore(flags); -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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