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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@redhat.com>
Reported-by: Carsten Emde <C.Emde@osadl.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2013-08-09 12:19:29 -07:00
parent 591c6d1710
commit 63c4db78e8
2 changed files with 37 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

28
include/trace/events/rcu.h
View File

@ -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,

18
kernel/rcutree.c
View File

@ -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) {