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rcu/nocb: Make rcu_core() callbacks acceleration (de-)offloading safe
When callbacks are offloaded, the NOCB kthreads handle the callbacks progression on behalf of rcu_core(). However during the (de-)offloading process, the kthread may not be entirely up to the task. As a result some callbacks grace period sequence number may remain stale for a while because rcu_core() won't take care of them either. Fix this with forcing callbacks acceleration from rcu_core() as long as the offloading process isn't complete. Reported-and-tested-by: Valentin Schneider <valentin.schneider@arm.com> Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Cc: Valentin Schneider <valentin.schneider@arm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Joel Fernandes <joel@joelfernandes.org> Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Neeraj Upadhyay <neeraju@codeaurora.org> Cc: Uladzislau Rezki <urezki@gmail.com> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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1 changed files with 16 additions and 2 deletions
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@ -2278,6 +2278,7 @@ rcu_report_qs_rdp(struct rcu_data *rdp)
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unsigned long flags;
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unsigned long mask;
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bool needwake = false;
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bool needacc = false;
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struct rcu_node *rnp;
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WARN_ON_ONCE(rdp->cpu != smp_processor_id());
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@ -2305,16 +2306,29 @@ rcu_report_qs_rdp(struct rcu_data *rdp)
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* This GP can't end until cpu checks in, so all of our
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* callbacks can be processed during the next GP.
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*
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* NOCB kthreads have their own way to deal with that.
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* NOCB kthreads have their own way to deal with that...
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*/
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if (!rcu_rdp_is_offloaded(rdp))
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if (!rcu_rdp_is_offloaded(rdp)) {
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needwake = rcu_accelerate_cbs(rnp, rdp);
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} else if (!rcu_segcblist_completely_offloaded(&rdp->cblist)) {
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/*
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* ...but NOCB kthreads may miss or delay callbacks acceleration
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* if in the middle of a (de-)offloading process.
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*/
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needacc = true;
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}
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rcu_disable_urgency_upon_qs(rdp);
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rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
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/* ^^^ Released rnp->lock */
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if (needwake)
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rcu_gp_kthread_wake();
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if (needacc) {
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rcu_nocb_lock_irqsave(rdp, flags);
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rcu_accelerate_cbs_unlocked(rnp, rdp);
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rcu_nocb_unlock_irqrestore(rdp, flags);
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}
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}
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}
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