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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 08/12] rcu: Improve diagnostics for failed RCU grace-period start Date: Wed, 9 Jan 2019 13:28:30 -0800 X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190109212816.GA32282@linux.ibm.com> References: <20190109212816.GA32282@linux.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 19010921-0064-0000-0000-0000039410D6 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00010375; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000274; SDB=6.01144145; UDB=6.00595708; IPR=6.00924407; MB=3.00025056; MTD=3.00000008; XFM=3.00000015; UTC=2019-01-09 21:28:40 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19010921-0065-0000-0000-00003BF962E3 Message-Id: <20190109212834.1257-8-paulmck@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-01-09_10:,, 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=8.0.1-1810050000 definitions=main-1901090171 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If a grace period fails to start (for example, because you commented out the last two lines of rcu_accelerate_cbs_unlocked()), rcu_core() will invoke rcu_check_gp_start_stall(), which will notice and complain. However, this complaint is lacking crucial debugging information such as when the last wakeup executed and what the value of ->gp_seq was at that time. This commit therefore removes the current pr_alert() from rcu_check_gp_start_stall(), instead invoking show_rcu_gp_kthreads(), which has been updated to print the needed information, which is collected by rcu_gp_kthread_wake(). Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 55 +++++++++++++++++++++++++++-------------------- kernel/rcu/tree.h | 2 ++ 2 files changed, 34 insertions(+), 23 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index b003a3cfe192..8543a90d53f2 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -512,6 +512,14 @@ void rcu_force_quiescent_state(void) } EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); +/* + * Return the root node of the rcu_state structure. + */ +static struct rcu_node *rcu_get_root(void) +{ + return &rcu_state.node[0]; +} + /* * Convert a ->gp_state value to a character string. */ @@ -529,19 +537,30 @@ void show_rcu_gp_kthreads(void) { int cpu; unsigned long j; + unsigned long ja; + unsigned long jr; + unsigned long jw; struct rcu_data *rdp; struct rcu_node *rnp; - j = jiffies - READ_ONCE(rcu_state.gp_activity); - pr_info("%s: wait state: %s(%d) ->state: %#lx delta ->gp_activity %ld\n", + j = jiffies; + ja = j - READ_ONCE(rcu_state.gp_activity); + jr = j - READ_ONCE(rcu_state.gp_req_activity); + jw = j - READ_ONCE(rcu_state.gp_wake_time); + pr_info("%s: wait state: %s(%d) ->state: %#lx delta ->gp_activity %lu ->gp_req_activity %lu ->gp_wake_time %lu ->gp_wake_seq %ld ->gp_seq %ld ->gp_seq_needed %ld ->gp_flags %#x\n", rcu_state.name, gp_state_getname(rcu_state.gp_state), - rcu_state.gp_state, rcu_state.gp_kthread->state, j); + rcu_state.gp_state, + rcu_state.gp_kthread ? rcu_state.gp_kthread->state : 0x1ffffL, + ja, jr, jw, (long)READ_ONCE(rcu_state.gp_wake_seq), + (long)READ_ONCE(rcu_state.gp_seq), + (long)READ_ONCE(rcu_get_root()->gp_seq_needed), + READ_ONCE(rcu_state.gp_flags)); rcu_for_each_node_breadth_first(rnp) { if (ULONG_CMP_GE(rcu_state.gp_seq, rnp->gp_seq_needed)) continue; - pr_info("\trcu_node %d:%d ->gp_seq %lu ->gp_seq_needed %lu\n", - rnp->grplo, rnp->grphi, rnp->gp_seq, - rnp->gp_seq_needed); + pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld\n", + rnp->grplo, rnp->grphi, (long)rnp->gp_seq, + (long)rnp->gp_seq_needed); if (!rcu_is_leaf_node(rnp)) continue; for_each_leaf_node_possible_cpu(rnp, cpu) { @@ -550,8 +569,8 @@ void show_rcu_gp_kthreads(void) ULONG_CMP_GE(rcu_state.gp_seq, rdp->gp_seq_needed)) continue; - pr_info("\tcpu %d ->gp_seq_needed %lu\n", - cpu, rdp->gp_seq_needed); + pr_info("\tcpu %d ->gp_seq_needed %ld\n", + cpu, (long)rdp->gp_seq_needed); } } /* sched_show_task(rcu_state.gp_kthread); */ @@ -577,14 +596,6 @@ void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags, } EXPORT_SYMBOL_GPL(rcutorture_get_gp_data); -/* - * Return the root node of the rcu_state structure. - */ -static struct rcu_node *rcu_get_root(void) -{ - return &rcu_state.node[0]; -} - /* * Enter an RCU extended quiescent state, which can be either the * idle loop or adaptive-tickless usermode execution. @@ -1560,7 +1571,8 @@ static bool rcu_future_gp_cleanup(struct rcu_node *rnp) * Awaken the grace-period kthread. Don't do a self-awaken, and don't * bother awakening when there is nothing for the grace-period kthread * to do (as in several CPUs raced to awaken, and we lost), and finally - * don't try to awaken a kthread that has not yet been created. + * don't try to awaken a kthread that has not yet been created. If + * all those checks are passed, track some debug information and awaken. */ static void rcu_gp_kthread_wake(void) { @@ -1568,6 +1580,8 @@ static void rcu_gp_kthread_wake(void) !READ_ONCE(rcu_state.gp_flags) || !rcu_state.gp_kthread) return; + WRITE_ONCE(rcu_state.gp_wake_time, jiffies); + WRITE_ONCE(rcu_state.gp_wake_seq, READ_ONCE(rcu_state.gp_seq)); swake_up_one(&rcu_state.gp_wq); } @@ -2657,16 +2671,11 @@ rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp, raw_spin_unlock_irqrestore_rcu_node(rnp, flags); return; } - pr_alert("%s: g%ld->%ld gar:%lu ga:%lu f%#x gs:%d %s->state:%#lx\n", - __func__, (long)READ_ONCE(rcu_state.gp_seq), - (long)READ_ONCE(rnp_root->gp_seq_needed), - j - rcu_state.gp_req_activity, j - rcu_state.gp_activity, - rcu_state.gp_flags, rcu_state.gp_state, rcu_state.name, - rcu_state.gp_kthread ? rcu_state.gp_kthread->state : 0x1ffffL); WARN_ON(1); if (rnp_root != rnp) raw_spin_unlock_rcu_node(rnp_root); raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + show_rcu_gp_kthreads(); } /* diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 008c356c7033..1f2ada7ef7d7 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -309,6 +309,8 @@ struct rcu_state { struct swait_queue_head gp_wq; /* Where GP task waits. */ short gp_flags; /* Commands for GP task. */ short gp_state; /* GP kthread sleep state. */ + unsigned long gp_wake_time; /* Last GP kthread wake. */ + unsigned long gp_wake_seq; /* ->gp_seq at ^^^. */ /* End of fields guarded by root rcu_node's lock. */ -- 2.17.1