diff options
| author | Frederic Weisbecker <frederic@kernel.org> | 2020-11-13 13:13:17 +0100 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2021-01-06 16:24:19 -0800 |
| commit | 8d346d438f93b5344e99d429727ec9c2f392d4ec (patch) | |
| tree | 88ab4e843d742d1ec3cf9c74cd111e662a8a6af9 /kernel/rcu/rcu_segcblist.h | |
| parent | 65e560327fe68153a9ad7452d5fd3171a1927d33 (diff) | |
rcu/nocb: Provide basic callback offloading state machine bits
Offloading and de-offloading RCU callback processes must be done
carefully. There must never be a time at which callback processing is
disabled because the task driving the offloading or de-offloading might be
preempted or otherwise stalled at that point in time, which would result
in OOM due to calbacks piling up indefinitely. This implies that there
will be times during which a given CPU's callbacks might be concurrently
invoked by both that CPU's RCU_SOFTIRQ handler (or, equivalently, that
CPU's rcuc kthread) and by that CPU's rcuo kthread.
This situation could fatally confuse both rcu_barrier() and the
CPU-hotplug offlining process, so these must be excluded during any
concurrent-callback-invocation period. In addition, during times of
concurrent callback invocation, changes to ->cblist must be protected
both as needed for RCU_SOFTIRQ and as needed for the rcuo kthread.
This commit therefore defines and documents the states for a state
machine that coordinates offloading and deoffloading.
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Inspired-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/rcu/rcu_segcblist.h')
| -rw-r--r-- | kernel/rcu/rcu_segcblist.h | 12 |
1 files changed, 10 insertions, 2 deletions
diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h index ff372db09f8b..e05952ab9b87 100644 --- a/kernel/rcu/rcu_segcblist.h +++ b/kernel/rcu/rcu_segcblist.h @@ -83,8 +83,16 @@ static inline bool rcu_segcblist_is_enabled(struct rcu_segcblist *rsclp) /* Is the specified rcu_segcblist offloaded? */ static inline bool rcu_segcblist_is_offloaded(struct rcu_segcblist *rsclp) { - return IS_ENABLED(CONFIG_RCU_NOCB_CPU) && - rcu_segcblist_test_flags(rsclp, SEGCBLIST_OFFLOADED); + if (IS_ENABLED(CONFIG_RCU_NOCB_CPU)) { + /* + * Complete de-offloading happens only when SEGCBLIST_SOFTIRQ_ONLY + * is set. + */ + if (!rcu_segcblist_test_flags(rsclp, SEGCBLIST_SOFTIRQ_ONLY)) + return true; + } + + return false; } /* |