diff options
| author | Frederic Weisbecker <frederic@kernel.org> | 2021-01-28 18:12:09 +0100 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2021-03-08 14:20:21 -0800 |
| commit | 64305db2856b969a5d48e8f3a5b0d06b5594591c (patch) | |
| tree | 52528ca44ad415bc4fb4d903a2890a0999bc0948 /kernel/rcu/tree.c | |
| parent | 5de2e5bb80aeef82f75fff76120874cdc86f935d (diff) | |
rcu/nocb: Forbid NOCB toggling on offline CPUs
It makes no sense to de-offload an offline CPU because that CPU will never
invoke any remaining callbacks. It also makes little sense to offload an
offline CPU because any pending RCU callbacks were migrated when that CPU
went offline. Yes, it is in theory possible to use a number of tricks
to permit offloading and deoffloading offline CPUs in certain cases, but
in practice it is far better to have the simple and deterministic rule
"Toggling the offload state of an offline CPU is forbidden".
For but one example, consider that an offloaded offline CPU might have
millions of callbacks queued. Best to just say "no".
This commit therefore forbids toggling of the offloaded state of
offline CPUs.
Reported-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: 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/tree.c')
| -rw-r--r-- | kernel/rcu/tree.c | 3 |
1 files changed, 1 insertions, 2 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 03503e295b51..ee77858403f8 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -4086,8 +4086,7 @@ int rcutree_prepare_cpu(unsigned int cpu) raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ /* * Lock in case the CB/GP kthreads are still around handling - * old callbacks (longer term we should flush all callbacks - * before completing CPU offline) + * old callbacks. */ rcu_nocb_lock(rdp); if (rcu_segcblist_empty(&rdp->cblist)) /* No early-boot CBs? */ |