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McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 4/5] rcu: Diagnostics for grace-period hangs Date: Mon, 25 Jun 2018 16:04:26 -0700 X-Mailer: git-send-email 2.17.1 In-Reply-To: <20180625230410.GA13250@linux.vnet.ibm.com> References: <20180625230410.GA13250@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 18062523-0068-0000-0000-0000030E1221 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009255; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000266; SDB=6.01052306; UDB=6.00539451; IPR=6.00830231; MB=3.00021855; MTD=3.00000008; XFM=3.00000015; UTC=2018-06-25 23:02:28 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18062523-0069-0000-0000-000044CEE5CD Message-Id: <20180625230427.13877-4-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-06-25_11:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=1 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1806210000 definitions=main-1806250260 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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: 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