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rcu/nocb: Don't invoke local rcu core on callback overload from nocb kthread

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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>
This commit is contained in:
Frederic Weisbecker 2021-10-19 02:08:16 +02:00 committed by Paul E. McKenney
parent a554ba2888
commit 0598a4d442
1 changed files with 5 additions and 5 deletions
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10
kernel/rcu/tree.c
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@ -2460,7 +2460,6 @@ static void rcu_do_batch(struct rcu_data *rdp)
int div; int div;
bool __maybe_unused empty; bool __maybe_unused empty;
unsigned long flags; unsigned long flags;
const bool offloaded = rcu_rdp_is_offloaded(rdp);
struct rcu_head *rhp; struct rcu_head *rhp;
struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl); struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
long bl, count = 0; long bl, count = 0;
@ -2582,9 +2581,6 @@ static void rcu_do_batch(struct rcu_data *rdp)
rcu_nocb_unlock_irqrestore(rdp, flags); rcu_nocb_unlock_irqrestore(rdp, flags);
/* Re-invoke RCU core processing if there are callbacks remaining. */
if (!offloaded && rcu_segcblist_ready_cbs(&rdp->cblist))
invoke_rcu_core();
tick_dep_clear_task(current, TICK_DEP_BIT_RCU); tick_dep_clear_task(current, TICK_DEP_BIT_RCU);
} }
@ -2771,8 +2767,12 @@ static __latent_entropy void rcu_core(void)
/* If there are callbacks ready, invoke them. */ /* If there are callbacks ready, invoke them. */
if (do_batch && rcu_segcblist_ready_cbs(&rdp->cblist) && if (do_batch && rcu_segcblist_ready_cbs(&rdp->cblist) &&
likely(READ_ONCE(rcu_scheduler_fully_active))) likely(READ_ONCE(rcu_scheduler_fully_active))) {
rcu_do_batch(rdp); rcu_do_batch(rdp);
/* Re-invoke RCU core processing if there are callbacks remaining. */
if (rcu_segcblist_ready_cbs(&rdp->cblist))
invoke_rcu_core();
}
/* Do any needed deferred wakeups of rcuo kthreads. */ /* Do any needed deferred wakeups of rcuo kthreads. */
do_nocb_deferred_wakeup(rdp); do_nocb_deferred_wakeup(rdp);