There is currently event tracing to track when a task is preempted
within a preemptible RCU read-side critical section, and also when that
task subsequently reaches its outermost rcu_read_unlock(), but none
indicating when a new grace period starts when that grace period must
wait on pre-existing readers that have been been preempted at least once
since the beginning of their current RCU read-side critical sections.
This commit therefore adds an event trace at grace-period start in
the case where there are such readers. Note that only the first
reader in the list is traced.
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
---
kernel/rcu/tree_plugin.h | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 14ba496a13cd..3e3f92e981a1 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -636,10 +636,17 @@ static int rcu_print_task_exp_stall(struct rcu_node *rnp)
*/
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
{
+ struct task_struct *t;
+
RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_check_blocked_tasks()
invoked with preemption enabled!!!\n");
WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
- if (rcu_preempt_has_tasks(rnp))
+ if (rcu_preempt_has_tasks(rnp)) {
rnp->gp_tasks = rnp->blkd_tasks.next;
+ t = container_of(rnp->gp_tasks, struct task_struct,
+ rcu_node_entry);
+ trace_rcu_unlock_preempted_task(TPS("rcu_preempt-GPS"),
+ rnp->gpnum, t->pid);
+ }
WARN_ON_ONCE(rnp->qsmask);
}
--
2.5.2
