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Date: Mon, 25 Jun 2018 16:04:26 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 4/5] rcu: Diagnostics for grace-period hangs
This commit causes a splat if RCU is idle and a request for a new grace
period is ignored for more than one second. This splat normally indicates
that some code path asked for a new grace period, but failed to wake up
the RCU grace-period kthread.
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
[ paulmck: Fix bug located by Dan Carpenter and his static checker. ]
---
kernel/rcu/tree.c | 63 +++++++++++++++++++++++++++++++++++++++++++++--
kernel/rcu/tree.h | 2 ++
2 files changed, 63 insertions(+), 2 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index b1fffa21b9e4..fae4df831e52 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1681,6 +1681,7 @@ static bool rcu_start_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,
}
trace_rcu_this_gp(rnp_root, rdp, c, TPS("Startedroot"));
WRITE_ONCE(rsp->gp_flags, rsp->gp_flags | RCU_GP_FLAG_INIT);
+ rsp->gp_req_activity = jiffies;
if (!rsp->gp_kthread) {
trace_rcu_this_gp(rnp_root, rdp, c, TPS("NoGPkthread"));
goto unlock_out;
@@ -2113,6 +2114,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
/* Advance CBs to reduce false positives below. */
if (!rcu_accelerate_cbs(rsp, rnp, rdp) && needgp) {
WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
+ rsp->gp_req_activity = jiffies;
trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gpnum),
TPS("newreq"));
}
@@ -2744,6 +2746,62 @@ static void force_quiescent_state(struct rcu_state *rsp)
rcu_gp_kthread_wake(rsp);
}
+/*
+ * This function checks for grace-period requests that fail to motivate
+ * RCU to come out of its idle mode.
+ */
+static void
+rcu_check_gp_start_stall(struct rcu_state *rsp, struct rcu_node *rnp,
+ struct rcu_data *rdp)
+{
+ unsigned long flags;
+ unsigned long j;
+ struct rcu_node *rnp_root = rcu_get_root(rsp);
+ static atomic_t warned = ATOMIC_INIT(0);
+
+ if (rcu_gp_in_progress(rsp) || !need_any_future_gp(rcu_get_root(rsp)))
+ return;
+ j = jiffies; /* Expensive access, and in common case don't get here. */
+ if (time_before(j, READ_ONCE(rsp->gp_req_activity) + HZ) ||
+ time_before(j, READ_ONCE(rsp->gp_activity) + HZ) ||
+ atomic_read(&warned))
+ return;
+
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ j = jiffies;
+ if (rcu_gp_in_progress(rsp) || !need_any_future_gp(rcu_get_root(rsp)) ||
+ time_before(j, READ_ONCE(rsp->gp_req_activity) + HZ) ||
+ time_before(j, READ_ONCE(rsp->gp_activity) + HZ) ||
+ atomic_read(&warned)) {
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ return;
+ }
+ /* Hold onto the leaf lock to make others see warned==1. */
+
+ raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */
+ j = jiffies;
+ if (rcu_gp_in_progress(rsp) || !need_any_future_gp(rcu_get_root(rsp)) ||
+ time_before(j, rsp->gp_req_activity + HZ) ||
+ time_before(j, rsp->gp_activity + HZ) ||
+ atomic_xchg(&warned, 1)) {
+ raw_spin_unlock_rcu_node(rnp_root); /* irqs remain disabled. */
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ return;
+ }
+ pr_alert("%s: g%lu %d%d%d%d gar:%lu ga:%lu f%#x %s->state:%#lx\n",
+ __func__, READ_ONCE(rsp->gpnum),
+ need_future_gp_element(rcu_get_root(rsp), 0),
+ need_future_gp_element(rcu_get_root(rsp), 1),
+ need_future_gp_element(rcu_get_root(rsp), 2),
+ need_future_gp_element(rcu_get_root(rsp), 3),
+ j - rsp->gp_req_activity, j - rsp->gp_activity,
+ rsp->gp_flags, rsp->name,
+ rsp->gp_kthread ? rsp->gp_kthread->state : 0x1ffffL);
+ WARN_ON(1);
+ raw_spin_unlock_rcu_node(rnp_root);
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+}
+
/*
* This does the RCU core processing work for the specified rcu_state
* and rcu_data structures. This may be called only from the CPU to
@@ -2755,7 +2813,7 @@ __rcu_process_callbacks(struct rcu_state *rsp)
unsigned long flags;
bool needwake;
struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
- struct rcu_node *rnp;
+ struct rcu_node *rnp = rdp->mynode;
WARN_ON_ONCE(!rdp->beenonline);
@@ -2769,7 +2827,6 @@ __rcu_process_callbacks(struct rcu_state *rsp)
if (rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL)) {
local_irq_restore(flags);
} else {
- rnp = rdp->mynode;
raw_spin_lock_rcu_node(rnp); /* irqs disabled. */
needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
@@ -2778,6 +2835,8 @@ __rcu_process_callbacks(struct rcu_state *rsp)
}
}
+ rcu_check_gp_start_stall(rsp, rnp, rdp);
+
/* If there are callbacks ready, invoke them. */
if (rcu_segcblist_ready_cbs(&rdp->cblist))
invoke_rcu_callbacks(rsp, rdp);
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 7365ac53fdd9..3c1942174c56 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -374,6 +374,8 @@ struct rcu_state {
/* but in jiffies. */
unsigned long gp_activity; /* Time of last GP kthread */
/* activity in jiffies. */
+ unsigned long gp_req_activity; /* Time of last GP request */
+ /* in jiffies. */
unsigned long jiffies_stall; /* Time at which to check */
/* for CPU stalls. */
unsigned long jiffies_resched; /* Time at which to resched */
--
2.17.1
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