From 63c4db78e80407976e47bccaa2a4d8251b5a10bc Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 9 Aug 2013 12:19:29 -0700 Subject: [PATCH] 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 Reported-by: Carsten Emde Signed-off-by: Paul E. McKenney --- 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 ee2376cfaab3..60077e12093c 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 6d028fdbf86c..78d371526667 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) { -- 2.34.1