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| author |  Paul E. McKenney <paulmck@kernel.org>
| 2021-09-29 11:09:34 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org>
| 2021-12-07 16:22:22 -0800 |
| commit | 790da248978a0722d92d1471630c881704f7eb0d (patch) | |
| tree | 1c78e09b356d5dec37b650046fe141c03418715c /kernel/rcu | |
| parent | rcu: Prevent expedited GP from enabling tick on offline CPU (diff) | |
| download | linux-790da248978a0722d92d1471630c881704f7eb0d.tar.gz linux-790da248978a0722d92d1471630c881704f7eb0d.tar.bz2 linux-790da248978a0722d92d1471630c881704f7eb0d.zip | |
rcu: Make idle entry report expedited quiescent states
In non-preemptible kernels, an unfortunately timed expedited grace period
can result in the rcu_exp_handler() IPI handler setting the rcu_data
structure's cpu_no_qs.b.exp field just as the target CPU enters idle.
There are situations in which this field will not be checked until after
that CPU exits idle. The resulting grace-period latency does not qualify
as "expedited".
This commit therefore checks this field upon non-preemptible idle entry in
the rcu_preempt_deferred_qs() function. It also qualifies the rcu_core()
preempt_count() check with IS_ENABLED(CONFIG_PREEMPT_COUNT) to prevent
false-positive quiescent states from count-free kernels.
Reported-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/rcu')
| -rw-r--r-- | kernel/rcu/tree.c | 2 | ||||
| -rw-r--r-- | kernel/rcu/tree_plugin.h | 13 |
2 files changed, 13 insertions, 2 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index ef8d36f580fc..a8d1fe35f482 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2714,7 +2714,7 @@ static __latent_entropy void rcu_core(void) WARN_ON_ONCE(!rdp->beenonline); /* Report any deferred quiescent states if preemption enabled. */ - if (!(preempt_count() & PREEMPT_MASK)) { + if (IS_ENABLED(CONFIG_PREEMPT_COUNT) && (!(preempt_count() & PREEMPT_MASK))) { rcu_preempt_deferred_qs(current); } else if (rcu_preempt_need_deferred_qs(current)) { set_tsk_need_resched(current); diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index e1a9fb96e0b9..8fb1612021a0 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -927,7 +927,18 @@ static bool rcu_preempt_need_deferred_qs(struct task_struct *t) { return false; } -static void rcu_preempt_deferred_qs(struct task_struct *t) { } + +// Except that we do need to respond to a request by an expedited grace +// period for a quiescent state from this CPU. Note that requests from +// tasks are handled when removing the task from the blocked-tasks list +// below. +static void rcu_preempt_deferred_qs(struct task_struct *t) +{ + struct rcu_data *rdp = this_cpu_ptr(&rcu_data); + + if (rdp->cpu_no_qs.b.exp) + rcu_report_exp_rdp(rdp); +} /* * Because there is no preemptible RCU, there can be no readers blocked, |