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McKenney" To: "He, Bo" Cc: Steven Rostedt , "linux-kernel@vger.kernel.org" , "josh@joshtriplett.org" , "mathieu.desnoyers@efficios.com" , "jiangshanlai@gmail.com" , "Zhang, Jun" , "Xiao, Jin" , "Zhang, Yanmin" , "Bai, Jie A" Subject: Re: rcu_preempt caused oom Reply-To: paulmck@linux.ibm.com References: <20181207141131.GP4170@linux.ibm.com> <20181209195601.GA7854@linux.ibm.com> <20181211003838.GD4170@linux.ibm.com> <20181211044631.GA19942@linux.ibm.com> <20181212022446.GV4170@linux.ibm.com> <20181212154224.GX4170@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181212154224.GX4170@linux.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18121221-0064-0000-0000-0000038548AF X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00010215; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000270; SDB=6.01130848; UDB=6.00587652; IPR=6.00910982; MB=3.00024673; MTD=3.00000008; XFM=3.00000015; UTC=2018-12-12 21:03:19 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18121221-0065-0000-0000-00003BA7D9A2 Message-Id: <20181212210316.GA14777@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-12-12_04:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 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-1812120179 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 12, 2018 at 07:42:24AM -0800, Paul E. McKenney wrote: > On Wed, Dec 12, 2018 at 01:21:33PM +0000, He, Bo wrote: > > we reproduce on two boards, but I still not see the show_rcu_gp_kthreads() dump logs, it seems the patch can't catch the scenario. > > I double confirmed the CONFIG_PROVE_RCU=y is enabled in the config as it's extracted from the /proc/config.gz. > > Strange. > > Are the systems responsive to sysrq keys once failure occurs? If so, I will > provide you a sysrq-R or some such to dump out the RCU state. Or, as it turns out, sysrq-y if booting with rcutree.sysrq_rcu=1 using the patch below. Only lightly tested. Thanx, Paul ------------------------------------------------------------------------ commit adfc7dff659495a3433d5084256be59eee0ac6df Author: Paul E. McKenney Date: Mon Dec 10 16:33:59 2018 -0800 rcu: Improve diagnostics for failed RCU grace-period start Backported from v4.21/v5.0 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 diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 0b760c1369f7..4bcd8753e293 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -626,25 +626,57 @@ void rcu_sched_force_quiescent_state(void) } EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state); +/* + * Convert a ->gp_state value to a character string. + */ +static const char *gp_state_getname(short gs) +{ + if (gs < 0 || gs >= ARRAY_SIZE(gp_state_names)) + return "???"; + return gp_state_names[gs]; +} + +/* + * Return the root node of the specified rcu_state structure. + */ +static struct rcu_node *rcu_get_root(struct rcu_state *rsp) +{ + return &rsp->node[0]; +} + /* * Show the state of the grace-period kthreads. */ 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; struct rcu_state *rsp; + j = jiffies; for_each_rcu_flavor(rsp) { - pr_info("%s: wait state: %d ->state: %#lx\n", - rsp->name, rsp->gp_state, rsp->gp_kthread->state); + ja = j - READ_ONCE(rsp->gp_activity); + jr = j - READ_ONCE(rsp->gp_req_activity); + jw = j - READ_ONCE(rsp->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", + rsp->name, gp_state_getname(rsp->gp_state), + rsp->gp_state, + rsp->gp_kthread ? rsp->gp_kthread->state : 0x1ffffL, + ja, jr, jw, (long)READ_ONCE(rsp->gp_wake_seq), + (long)READ_ONCE(rsp->gp_seq), + (long)READ_ONCE(rcu_get_root(rsp)->gp_seq_needed), + READ_ONCE(rsp->gp_flags)); rcu_for_each_node_breadth_first(rsp, rnp) { if (ULONG_CMP_GE(rsp->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) { @@ -653,8 +685,8 @@ void show_rcu_gp_kthreads(void) ULONG_CMP_GE(rsp->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(rsp->gp_kthread); */ @@ -690,14 +722,6 @@ 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 specified rcu_state structure. - */ -static struct rcu_node *rcu_get_root(struct rcu_state *rsp) -{ - return &rsp->node[0]; -} - /* * Enter an RCU extended quiescent state, which can be either the * idle loop or adaptive-tickless usermode execution. @@ -1285,16 +1309,6 @@ static void record_gp_stall_check_time(struct rcu_state *rsp) rsp->n_force_qs_gpstart = READ_ONCE(rsp->n_force_qs); } -/* - * Convert a ->gp_state value to a character string. - */ -static const char *gp_state_getname(short gs) -{ - if (gs < 0 || gs >= ARRAY_SIZE(gp_state_names)) - return "???"; - return gp_state_names[gs]; -} - /* * Complain about starvation of grace-period kthread. */ @@ -1693,7 +1707,8 @@ static bool rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) * 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. + * 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(struct rcu_state *rsp) { @@ -1701,6 +1716,8 @@ static void rcu_gp_kthread_wake(struct rcu_state *rsp) !READ_ONCE(rsp->gp_flags) || !rsp->gp_kthread) return; + WRITE_ONCE(rsp->gp_wake_time, jiffies); + WRITE_ONCE(rsp->gp_wake_seq, READ_ONCE(rsp->gp_seq)); swake_up_one(&rsp->gp_wq); } @@ -2802,16 +2819,11 @@ rcu_check_gp_start_stall(struct rcu_state *rsp, struct rcu_node *rnp, 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(rsp->gp_seq), - (long)READ_ONCE(rnp_root->gp_seq_needed), - j - rsp->gp_req_activity, j - rsp->gp_activity, - rsp->gp_flags, rsp->gp_state, rsp->name, - rsp->gp_kthread ? rsp->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 4e74df768c57..0e051d9b5f1a 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -327,6 +327,8 @@ 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. */