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rcu/nocb: Shutdown nocb timer on de-offloading 

This commit ensures that the nocb timer is shut down before reaching the
final de-offloaded state.  The key goal is to prevent the timer handler
from manipulating the callbacks without the protection of the nocb locks.

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>
This commit is contained in:
Frederic Weisbecker 2020-11-13 13:13:23 +01:00 committed by Paul E. McKenney
parent 254e11efde
commit 69cdea873c
2 changed files with 12 additions and 1 deletions
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1
kernel/rcu/tree.h
View File

@ -257,6 +257,7 @@ struct rcu_data {
};
/* Values for nocb_defer_wakeup field in struct rcu_data. */
#define RCU_NOCB_WAKE_OFF -1
#define RCU_NOCB_WAKE_NOT 0
#define RCU_NOCB_WAKE 1
#define RCU_NOCB_WAKE_FORCE 2

12
kernel/rcu/tree_plugin.h
View File

@ -1665,6 +1665,8 @@ static void wake_nocb_gp(struct rcu_data *rdp, bool force,
static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype,
const char *reason)
{
if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_OFF)
return;
if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT)
mod_timer(&rdp->nocb_timer, jiffies + 1);
if (rdp->nocb_defer_wakeup < waketype)
@ -2243,7 +2245,7 @@ static int rcu_nocb_cb_kthread(void *arg)
/* Is a deferred wakeup of rcu_nocb_kthread() required? */
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
{
return READ_ONCE(rdp->nocb_defer_wakeup);
return READ_ONCE(rdp->nocb_defer_wakeup) > RCU_NOCB_WAKE_NOT;
}
/* Do a deferred wakeup of rcu_nocb_kthread(). */
@ -2337,6 +2339,12 @@ static int __rcu_nocb_rdp_deoffload(struct rcu_data *rdp)
swait_event_exclusive(rdp->nocb_state_wq,
!rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB |
SEGCBLIST_KTHREAD_GP));
/* Make sure nocb timer won't stay around */
rcu_nocb_lock_irqsave(rdp, flags);
WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_OFF);
rcu_nocb_unlock_irqrestore(rdp, flags);
del_timer_sync(&rdp->nocb_timer);
return ret;
}
@ -2394,6 +2402,8 @@ static int __rcu_nocb_rdp_offload(struct rcu_data *rdp)
* SEGCBLIST_SOFTIRQ_ONLY mode.
*/
raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
/* Re-enable nocb timer */
WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
/*
* We didn't take the nocb lock while working on the
* rdp->cblist in SEGCBLIST_SOFTIRQ_ONLY mode.