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RCU fix for v6.12

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Fix rcuog kthread wakeup invocation from softirq context on a CPU
 which has been marked offline. This can happen when new callbacks
 are enqueued from a softirq on an offline CPU before it calls
 rcutree_report_cpu_dead(). When this happens on NOCB configuration,
 the rcuog wake-up is deferred through an IPI to an online CPU.
 This is done to avoid call into the scheduler which can risk
 arming the RT-bandwidth after hrtimers have been migrated out
 and disabled. However, doing IPI call from softirq is not allowed
 Fix this by forcing deferred rcuog wakeup through the NOCB timer
 when the CPU is offline.
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Merge tag 'rcu.fixes.6.12-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux

Pull RCU fix from Neeraj Upadhyay:
 "Fix rcuog kthread wakeup invocation from softirq context on a CPU
  which has been marked offline.

  This can happen when new callbacks are enqueued from a softirq on an
  offline CPU before it calls rcutree_report_cpu_dead(). When this
  happens on NOCB configuration, the rcuog wake-up is deferred through
  an IPI to an online CPU. This is done to avoid call into the scheduler
  which can risk arming the RT-bandwidth after hrtimers have been
  migrated out and disabled.

  However, doing IPI call from softirq is not allowed: Fix this by
  forcing deferred rcuog wakeup through the NOCB timer when the CPU is
  offline"

* tag 'rcu.fixes.6.12-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux:
  rcu/nocb: Fix rcuog wake-up from offline softirq
This commit is contained in:
Linus Torvalds 2024-10-11 14:42:27 -07:00
commit a1029768f3
1 changed files with 7 additions and 1 deletions
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8
kernel/rcu/tree_nocb.h
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@ -554,13 +554,19 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
rcu_nocb_unlock(rdp);
wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_LAZY,
TPS("WakeLazy"));
} else if (!irqs_disabled_flags(flags)) {
} else if (!irqs_disabled_flags(flags) && cpu_online(rdp->cpu)) {
/* ... if queue was empty ... */
rcu_nocb_unlock(rdp);
wake_nocb_gp(rdp, false);
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
TPS("WakeEmpty"));
} else {
/*
* Don't do the wake-up upfront on fragile paths.
* Also offline CPUs can't call swake_up_one_online() from
* (soft-)IRQs. Rely on the final deferred wake-up from
* rcutree_report_cpu_dead()
*/
rcu_nocb_unlock(rdp);
wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE,
TPS("WakeEmptyIsDeferred"));