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author | Frederic Weisbecker <frederic@kernel.org> | 2021-10-19 02:08:16 +0200 |
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committer | Paul E. McKenney <paulmck@kernel.org> | 2021-12-07 16:24:44 -0800 |
commit | 0598a4d4429c0a952ac0e99e5280354cf4ccc01c (patch) | |
tree | cdad9a87f658e3f56a89cb19436e96725012fbd9 /kernel/rcu/tree.c | |
parent | a554ba288845fd3f6f12311fd76a51694233458a (diff) | |
download | linux-0598a4d4429c0a952ac0e99e5280354cf4ccc01c.tar.gz linux-0598a4d4429c0a952ac0e99e5280354cf4ccc01c.tar.bz2 linux-0598a4d4429c0a952ac0e99e5280354cf4ccc01c.zip |
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>
Diffstat (limited to 'kernel/rcu/tree.c')
-rw-r--r-- | kernel/rcu/tree.c | 10 |
1 files changed, 5 insertions, 5 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 1b31fad9f1a0..03c038f324a0 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2460,7 +2460,6 @@ static void rcu_do_batch(struct rcu_data *rdp) int div; bool __maybe_unused empty; unsigned long flags; - const bool offloaded = rcu_rdp_is_offloaded(rdp); struct rcu_head *rhp; struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl); long bl, count = 0; @@ -2582,9 +2581,6 @@ static void rcu_do_batch(struct rcu_data *rdp) 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); } @@ -2771,8 +2767,12 @@ static __latent_entropy void rcu_core(void) /* If there are callbacks ready, invoke them. */ 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); + /* 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_nocb_deferred_wakeup(rdp); |