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    Subject[PATCH 6.0 665/862] rcu-tasks: Ensure RCU Tasks Trace loops have quiescent states
    Date
    From: Paul E. McKenney <paulmck@kernel.org>

    [ Upstream commit d6ad60635cafe900bcd11ad588d8accb36c36b1b ]

    The RCU Tasks Trace grace-period kthread loops across all CPUs, and
    there can be quite a few CPUs, with some commercially available systems
    sporting well over a thousand of them. Some of these loops can feature
    IPIs, which can take some time. This commit therefore places a call to
    cond_resched_tasks_rcu_qs() in each such loop.

    Link: https://docs.google.com/document/d/1V0YnG1HTWMt9WHJjroiJL9lf-hMrud4v8Fn3fhyY0cI/edit?usp=sharing
    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    kernel/rcu/tasks.h | 3 +++
    1 file changed, 3 insertions(+)

    diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
    index 469bf2a3b505..f5bf6fb430da 100644
    --- a/kernel/rcu/tasks.h
    +++ b/kernel/rcu/tasks.h
    @@ -1500,6 +1500,7 @@ static void rcu_tasks_trace_pregp_step(struct list_head *hop)
    if (rcu_tasks_trace_pertask_prep(t, true))
    trc_add_holdout(t, hop);
    rcu_read_unlock();
    + cond_resched_tasks_rcu_qs();
    }

    // Only after all running tasks have been accounted for is it
    @@ -1520,6 +1521,7 @@ static void rcu_tasks_trace_pregp_step(struct list_head *hop)
    raw_spin_lock_irqsave_rcu_node(rtpcp, flags);
    }
    raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
    + cond_resched_tasks_rcu_qs();
    }

    // Re-enable CPU hotplug now that the holdout list is populated.
    @@ -1619,6 +1621,7 @@ static void check_all_holdout_tasks_trace(struct list_head *hop,
    trc_del_holdout(t);
    else if (needreport)
    show_stalled_task_trace(t, firstreport);
    + cond_resched_tasks_rcu_qs();
    }

    // Re-enable CPU hotplug now that the holdout list scan has completed.
    --
    2.35.1


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