linux-kernel - Re: [PATCH v3] rcu: Dump all rcuc kthreads status for CPUs that not report quiescent state

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Message-ID: <202204241503.imwh5SqZ-lkp@intel.com>
Date:   Mon, 25 Apr 2022 16:23:55 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     kbuild@...ts.01.org, Zqiang <qiang1.zhang@...el.com>,
        paulmck@...nel.org, frederic@...nel.org
Cc:     lkp@...el.com, kbuild-all@...ts.01.org, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] rcu: Dump all rcuc kthreads status for CPUs that not
 report quiescent state

Hi Zqiang,

url:    https://github.com/intel-lab-lkp/linux/commits/Zqiang/rcu-Dump-all-rcuc-kthreads-status-for-CPUs-that-not-report-quiescent-state/20220424-121850
base:   https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev
config: i386-randconfig-m021 (https://download.01.org/0day-ci/archive/20220424/202204241503.imwh5SqZ-lkp@intel.com/config)
compiler: gcc-11 (Debian 11.2.0-20) 11.2.0

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@...el.com>
Reported-by: Dan Carpenter <dan.carpenter@...cle.com>

smatch warnings:
kernel/rcu/tree_stall.h:467 print_cpu_stall_info() error: uninitialized symbol 'j'.

vim +/j +467 kernel/rcu/tree_stall.h

59b73a27681c58 Paul E. McKenney 2019-01-11  440  static void print_cpu_stall_info(int cpu)
59b73a27681c58 Paul E. McKenney 2019-01-11  441  {
59b73a27681c58 Paul E. McKenney 2019-01-11  442  	unsigned long delta;
88375825171c7d Paul E. McKenney 2020-03-31  443  	bool falsepositive;
59b73a27681c58 Paul E. McKenney 2019-01-11  444  	struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
59b73a27681c58 Paul E. McKenney 2019-01-11  445  	char *ticks_title;
59b73a27681c58 Paul E. McKenney 2019-01-11  446  	unsigned long ticks_value;
17d9de741a1aaf Zqiang           2022-04-24  447  	bool rcuc_starved;
17d9de741a1aaf Zqiang           2022-04-24  448  	unsigned long j;
59b73a27681c58 Paul E. McKenney 2019-01-11  449  
59b73a27681c58 Paul E. McKenney 2019-01-11  450  	/*
59b73a27681c58 Paul E. McKenney 2019-01-11  451  	 * We could be printing a lot while holding a spinlock.  Avoid
59b73a27681c58 Paul E. McKenney 2019-01-11  452  	 * triggering hard lockup.
59b73a27681c58 Paul E. McKenney 2019-01-11  453  	 */
59b73a27681c58 Paul E. McKenney 2019-01-11  454  	touch_nmi_watchdog();
59b73a27681c58 Paul E. McKenney 2019-01-11  455  
59b73a27681c58 Paul E. McKenney 2019-01-11  456  	ticks_value = rcu_seq_ctr(rcu_state.gp_seq - rdp->gp_seq);
59b73a27681c58 Paul E. McKenney 2019-01-11  457  	if (ticks_value) {
59b73a27681c58 Paul E. McKenney 2019-01-11  458  		ticks_title = "GPs behind";
59b73a27681c58 Paul E. McKenney 2019-01-11  459  	} else {
59b73a27681c58 Paul E. McKenney 2019-01-11  460  		ticks_title = "ticks this GP";
59b73a27681c58 Paul E. McKenney 2019-01-11  461  		ticks_value = rdp->ticks_this_gp;
59b73a27681c58 Paul E. McKenney 2019-01-11  462  	}
59b73a27681c58 Paul E. McKenney 2019-01-11  463  	delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq);
88375825171c7d Paul E. McKenney 2020-03-31  464  	falsepositive = rcu_is_gp_kthread_starving(NULL) &&
88375825171c7d Paul E. McKenney 2020-03-31  465  			rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp));
17d9de741a1aaf Zqiang           2022-04-24  466  	rcuc_starved = rcu_is_rcuc_kthread_starving(rdp, &j);


That tree has some new returns in rcu_is_rcuc_kthread_starving() where
*jp is not set.

17d9de741a1aaf Zqiang           2022-04-24 @467  	pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld rcuc=%ld jiffies(%s) %s\n",
59b73a27681c58 Paul E. McKenney 2019-01-11  468  	       cpu,
59b73a27681c58 Paul E. McKenney 2019-01-11  469  	       "O."[!!cpu_online(cpu)],
59b73a27681c58 Paul E. McKenney 2019-01-11  470  	       "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],
59b73a27681c58 Paul E. McKenney 2019-01-11  471  	       "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)],
59b73a27681c58 Paul E. McKenney 2019-01-11  472  	       !IS_ENABLED(CONFIG_IRQ_WORK) ? '?' :
59b73a27681c58 Paul E. McKenney 2019-01-11  473  			rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' :
59b73a27681c58 Paul E. McKenney 2019-01-11  474  				"!."[!delta],
59b73a27681c58 Paul E. McKenney 2019-01-11  475  	       ticks_value, ticks_title,
59b73a27681c58 Paul E. McKenney 2019-01-11  476  	       rcu_dynticks_snap(rdp) & 0xfff,
59b73a27681c58 Paul E. McKenney 2019-01-11  477  	       rdp->dynticks_nesting, rdp->dynticks_nmi_nesting,
59b73a27681c58 Paul E. McKenney 2019-01-11  478  	       rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
88375825171c7d Paul E. McKenney 2020-03-31  479  	       data_race(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart,
17d9de741a1aaf Zqiang           2022-04-24  480  	       j, rcuc_starved ? "starved" : "",
88375825171c7d Paul E. McKenney 2020-03-31  481  	       falsepositive ? " (false positive?)" : "");
59b73a27681c58 Paul E. McKenney 2019-01-11  482  }

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