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rcu/nocb: Don't invoke local rcu core on callback overload from nocb kthread
rcu_core() tries to ensure that its self-invocation in case of callbacks overload only happen in softirq/rcuc mode. Indeed it doesn't make sense to trigger local RCU core from nocb_cb kthread since it can execute on a CPU different from the target rdp. Also in case of overload, the nocb_cb kthread simply iterates a new loop of callbacks processing. However the "offloaded" check that aims at preventing misplaced rcu_core() invocations is wrong. First of all that state is volatile and second: softirq/rcuc can execute while the target rdp is offloaded. As a result rcu_core() can be invoked on the wrong CPU while in the process of (de-)offloading. Fix that with moving the rcu_core() self-invocation to rcu_core() itself, irrespective of the rdp offloaded state. 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 5 additions and 5 deletions
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@ -2460,7 +2460,6 @@ static void rcu_do_batch(struct rcu_data *rdp)
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int div;
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bool __maybe_unused empty;
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unsigned long flags;
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const bool offloaded = rcu_rdp_is_offloaded(rdp);
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struct rcu_head *rhp;
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struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
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long bl, count = 0;
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@ -2582,9 +2581,6 @@ static void rcu_do_batch(struct rcu_data *rdp)
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rcu_nocb_unlock_irqrestore(rdp, flags);
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/* Re-invoke RCU core processing if there are callbacks remaining. */
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if (!offloaded && rcu_segcblist_ready_cbs(&rdp->cblist))
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invoke_rcu_core();
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tick_dep_clear_task(current, TICK_DEP_BIT_RCU);
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}
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@ -2771,8 +2767,12 @@ static __latent_entropy void rcu_core(void)
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/* If there are callbacks ready, invoke them. */
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if (do_batch && rcu_segcblist_ready_cbs(&rdp->cblist) &&
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likely(READ_ONCE(rcu_scheduler_fully_active)))
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likely(READ_ONCE(rcu_scheduler_fully_active))) {
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rcu_do_batch(rdp);
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/* Re-invoke RCU core processing if there are callbacks remaining. */
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if (rcu_segcblist_ready_cbs(&rdp->cblist))
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invoke_rcu_core();
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}
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/* Do any needed deferred wakeups of rcuo kthreads. */
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do_nocb_deferred_wakeup(rdp);
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