Commit c4402b27 authored Nov 09, 2016 by Byungchul Park Committed by Paul E. McKenney Jan 23, 2017

rcu: Only dump stalled-tasks stacks if there was a real stall



The print_other_cpu_stall() function currently unconditionally invokes
rcu_print_detail_task_stall().  This is OK because if there was a stall
sufficient to cause print_other_cpu_stall() to be invoked, that stall
is very likely to persist through the entire print_other_cpu_stall()
execution.  However, if the stall did not persist, the variable ndetected
will be zero, and that variable is already tested in an "if" statement.
Therefore, this commit moves the call to rcu_print_detail_task_stall()
under that pre-existing "if" to improve readability, with a very rare
reduction in overhead.

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
[ paulmck: Reworked commit log. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

parent 90756533

kernel/rcu/tree.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -1379,6 +1379,9 @@ static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
		(long)rsp->gpnum, (long)rsp->completed, totqlen);
		if (ndetected) {
		rcu_dump_cpu_stacks(rsp);

		/* Complain about tasks blocking the grace period. */
		rcu_print_detail_task_stall(rsp);
		} else {
		if (READ_ONCE(rsp->gpnum) != gpnum \|\|
		READ_ONCE(rsp->completed) == gpnum) {
		@@ -1395,9 +1398,6 @@ static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
		}
		}

		/* Complain about tasks blocking the grace period. */
		rcu_print_detail_task_stall(rsp);

		rcu_check_gp_kthread_starvation(rsp);

		panic_on_rcu_stall();

Admin message