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rcu: Add irqs-disabled indicator to expedited RCU CPU stall warnings
If a CPU has interrupts disabled continuously starting before the beginning of a given expedited RCU grace period, that CPU will not execute that grace period's IPI handler. This will in turn mean that the ->cpu_no_qs.b.exp field in that CPU's rcu_data structure will continue to contain the boolean value false. Knowing whether or not a CPU has had interrupts disabled can be helpful when debugging an expedited RCU CPU stall warning, so this commit adds a "D" indicator expedited RCU CPU stall warnings that signifies that the corresponding CPU has had interrupts disabled throughout. This capability was tested as follows: runqemu kvm slirp nographic qemuparams="-m 4096 -smp 4" bootparams= "isolcpus=2,3 nohz_full=2,3 rcu_nocbs=2,3 rcutree.dump_tree=1 rcutorture.stall_cpu_holdoff=30 rcutorture.stall_cpu=40 rcutorture.stall_cpu_irqsoff=1 rcutorture.stall_cpu_block=0 rcutorture.stall_no_softlockup=1" -d The rcu_torture_stall() function ran on CPU 1, which displays the "D" as expected given the rcutorture.stall_cpu_irqsoff=1 module parameter: ............ rcu: INFO: rcu_preempt detected expedited stalls on CPUs/tasks: { 1-...D } 26467 jiffies s: 13317 root: 0x1/. rcu: blocking rcu_node structures (internal RCU debug): l=1:0-1:0x2/. Task dump for CPU 1: task:rcu_torture_sta state:R running task stack: 0 pid: 76 ppid: 2 flags:0x00004008 Signed-off-by: Zqiang <qiang1.zhang@intel.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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@ -637,10 +637,11 @@ static void synchronize_rcu_expedited_wait(void)
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continue;
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ndetected++;
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rdp = per_cpu_ptr(&rcu_data, cpu);
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pr_cont(" %d-%c%c%c", cpu,
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pr_cont(" %d-%c%c%c%c", cpu,
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"O."[!!cpu_online(cpu)],
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"o."[!!(rdp->grpmask & rnp->expmaskinit)],
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"N."[!!(rdp->grpmask & rnp->expmaskinitnext)]);
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"N."[!!(rdp->grpmask & rnp->expmaskinitnext)],
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"D."[!!(rdp->cpu_no_qs.b.exp)]);
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}
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}
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pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",
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