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Date: Fri, 27 Mar 2020 15:24:51 -0700 From: paulmck@...nel.org To: rcu@...r.kernel.org Cc: linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com, akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com, josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org, "Paul E. McKenney" <paulmck@...nel.org> Subject: [PATCH v3 tip/core/rcu 29/34] rcu-tasks: Handle the running-offline idle-task special case From: "Paul E. McKenney" <paulmck@...nel.org> The idle task corresponding to an offline CPU can appear to be running while that CPU is offline. This commit therefore adds checks for this situation, treating it as a quiescent state. Because the tasklist scan and the holdout-list scan now exclude CPU-hotplug operations, readers on the CPU-hotplug paths are still waited for. Signed-off-by: Paul E. McKenney <paulmck@...nel.org> --- kernel/rcu/tasks.h | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index df6e785..d1fa7715 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -818,16 +818,20 @@ static bool trc_inspect_reader(struct task_struct *t, void *arg) { int cpu = task_cpu(t); bool in_qs = false; + bool ofl = cpu_is_offline(cpu); if (task_curr(t)) { + WARN_ON_ONCE(ofl & !is_idle_task(t)); + // If no chance of heavyweight readers, do it the hard way. - if (!IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) + if (!ofl && !IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) return false; // If heavyweight readers are enabled on the remote task, // we can inspect its state despite its currently running. // However, we cannot safely change its state. - if (!rcu_dynticks_zero_in_eqs(cpu, &t->trc_reader_nesting)) + if (!ofl && // Check for "running" idle tasks on offline CPUs. + !rcu_dynticks_zero_in_eqs(cpu, &t->trc_reader_nesting)) return false; // No quiescent state, do it the hard way. in_qs = true; } else { -- 2.9.5
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