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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>
This commit is contained in:
Byungchul Park 2016-11-09 17:57:13 +09:00 committed by Paul E. McKenney
parent 907565337e
commit c4402b27f1
1 changed files with 3 additions and 3 deletions
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6
kernel/rcu/tree.c
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@ -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();