Commit-ID: 63c4db78e80407976e47bccaa2a4d8251b5a10bc
Gitweb: http://git.kernel.org/tip/63c4db78e80407976e47bccaa2a4d8251b5a10bc
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Fri, 9 Aug 2013 12:19:29 -0700
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Mon, 23 Sep 2013 09:16:14 -0700
rcu: Add tracing to rcu_gp_kthread()
This commit adds tracing to the rcu_gp_kthread() function in order to
help trace down hangs potentially involving this kthread.
Reported-by: Clark Williams <williams@xxxxxxxxxx>
Reported-by: Carsten Emde <C.Emde@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
include/trace/events/rcu.h | 28 +++++++++++++++++++---------
kernel/rcutree.c | 18 ++++++++++++++++++
2 files changed, 37 insertions(+), 9 deletions(-)
diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index ee2376c..60077e1 100644
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -39,15 +39,25 @@ TRACE_EVENT(rcu_utilization,
#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
/*
- * Tracepoint for grace-period events: starting and ending a grace
- * period ("start" and "end", respectively), a CPU noting the start
- * of a new grace period or the end of an old grace period ("cpustart"
- * and "cpuend", respectively), a CPU passing through a quiescent
- * state ("cpuqs"), a CPU coming online or going offline ("cpuonl"
- * and "cpuofl", respectively), a CPU being kicked for being too
- * long in dyntick-idle mode ("kick"), a CPU accelerating its new
- * callbacks to RCU_NEXT_READY_TAIL ("AccReadyCB"), and a CPU
- * accelerating its new callbacks to RCU_WAIT_TAIL ("AccWaitCB").
+ * Tracepoint for grace-period events. Takes a string identifying the
+ * RCU flavor, the grace-period number, and a string identifying the
+ * grace-period-related event as follows:
+ *
+ * "AccReadyCB": CPU acclerates new callbacks to RCU_NEXT_READY_TAIL.
+ * "AccWaitCB": CPU accelerates new callbacks to RCU_WAIT_TAIL.
+ * "start": Start a grace period.
+ * "cpustart": CPU first notices a grace-period start.
+ * "cpuqs": CPU passes through a quiescent state.
+ * "cpuonl": CPU comes online.
+ * "cpuofl": CPU goes offline.
+ * "reqwait": GP kthread sleeps waiting for grace-period request.
+ * "reqwaitsig": GP kthread awakened by signal from reqwait state.
+ * "fqswait": GP kthread waiting until time to force quiescent states.
+ * "fqsstart": GP kthread starts forcing quiescent states.
+ * "fqsend": GP kthread done forcing quiescent states.
+ * "fqswaitsig": GP kthread awakened by signal from fqswait state.
+ * "end": End a grace period.
+ * "cpuend": CPU first notices a grace-period end.
*/
TRACE_EVENT(rcu_grace_period,
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 6d028fd..78d3715 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1480,6 +1480,9 @@ static int __noreturn rcu_gp_kthread(void *arg)
/* Handle grace-period start. */
for (;;) {
+ trace_rcu_grace_period(rsp->name,
+ ACCESS_ONCE(rsp->gpnum),
+ TPS("reqwait"));
wait_event_interruptible(rsp->gp_wq,
ACCESS_ONCE(rsp->gp_flags) &
RCU_GP_FLAG_INIT);
@@ -1487,6 +1490,9 @@ static int __noreturn rcu_gp_kthread(void *arg)
break;
cond_resched();
flush_signals(current);
+ trace_rcu_grace_period(rsp->name,
+ ACCESS_ONCE(rsp->gpnum),
+ TPS("reqwaitsig"));
}
/* Handle quiescent-state forcing. */
@@ -1500,6 +1506,9 @@ static int __noreturn rcu_gp_kthread(void *arg)
for (;;) {
if (!ret)
rsp->jiffies_force_qs = jiffies + j;
+ trace_rcu_grace_period(rsp->name,
+ ACCESS_ONCE(rsp->gpnum),
+ TPS("fqswait"));
ret = wait_event_interruptible_timeout(rsp->gp_wq,
((gf = ACCESS_ONCE(rsp->gp_flags)) &
RCU_GP_FLAG_FQS) ||
@@ -1513,12 +1522,21 @@ static int __noreturn rcu_gp_kthread(void *arg)
/* If time for quiescent-state forcing, do it. */
if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) ||
(gf & RCU_GP_FLAG_FQS)) {
+ trace_rcu_grace_period(rsp->name,
+ ACCESS_ONCE(rsp->gpnum),
+ TPS("fqsstart"));
fqs_state = rcu_gp_fqs(rsp, fqs_state);
+ trace_rcu_grace_period(rsp->name,
+ ACCESS_ONCE(rsp->gpnum),
+ TPS("fqsend"));
cond_resched();
} else {
/* Deal with stray signal. */
cond_resched();
flush_signals(current);
+ trace_rcu_grace_period(rsp->name,
+ ACCESS_ONCE(rsp->gpnum),
+ TPS("fqswaitsig"));
}
j = jiffies_till_next_fqs;
if (j > HZ) {
--
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