From: "Paul E. McKenney" <paulmck@kernel.org>
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
mingo@kernel.org, jiangshanlai@gmail.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
"Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH tip/core/rcu 26/26] rcu: Don't penalize priority boosting when there is nothing to boost
Date: Tue, 11 May 2021 16:12:23 -0700 [thread overview]
Message-ID: <20210511231223.2895398-26-paulmck@kernel.org> (raw)
In-Reply-To: <20210511231149.GA2895263@paulmck-ThinkPad-P17-Gen-1>
RCU priority boosting cannot do anything unless there is at least one
task blocking the current RCU grace period that was preempted within
the RCU read-side critical section that it still resides in. However,
the current rcu_torture_boost_failed() code will count this as an RCU
priority-boosting failure if there were no CPUs blocking the current
grace period. This situation can happen (for example) if the last CPU
blocking the current grace period was subjected to vCPU preemption,
which is always a risk for rcutorture guest OSes.
This commit therefore causes rcu_torture_boost_failed() to refrain from
reporting failure unless there is at least one task blocking the current
RCU grace period that was preempted within the RCU read-side critical
section that it still resides in.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/tree_stall.h | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 8bde1b53b0c9..65302518e006 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -723,6 +723,10 @@ static void check_cpu_stall(struct rcu_data *rdp)
* count this as an RCU priority boosting failure. A return of true says
* RCU priority boosting is to blame, and false says otherwise. If false
* is returned, the first of the CPUs to blame is stored through cpup.
+ * If there was no CPU blocking the current grace period, but also nothing
+ * in need of being boosted, *cpup is set to -1. This can happen in case
+ * of vCPU preemption while the last CPU is reporting its quiscent state,
+ * for example.
*
* If cpup is NULL, then a lockless quick check is carried out, suitable
* for high-rate usage. On the other hand, if cpup is non-NULL, each
@@ -730,18 +734,25 @@ static void check_cpu_stall(struct rcu_data *rdp)
*/
bool rcu_check_boost_fail(unsigned long gp_state, int *cpup)
{
+ bool atb = false;
int cpu;
unsigned long flags;
struct rcu_node *rnp;
rcu_for_each_leaf_node(rnp) {
if (!cpup) {
- if (READ_ONCE(rnp->qsmask))
+ if (READ_ONCE(rnp->qsmask)) {
return false;
- else
+ } else {
+ if (READ_ONCE(rnp->gp_tasks))
+ atb = true;
continue;
+ }
}
+ *cpup = -1;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ if (rnp->gp_tasks)
+ atb = true;
if (!rnp->qsmask) {
// No CPUs without quiescent states for this rnp.
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
@@ -758,7 +769,7 @@ bool rcu_check_boost_fail(unsigned long gp_state, int *cpup)
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
// Can't blame CPUs, so must blame RCU priority boosting.
- return true;
+ return atb;
}
EXPORT_SYMBOL_GPL(rcu_check_boost_fail);
--
2.31.1.189.g2e36527f23
next prev parent reply other threads:[~2021-05-11 23:13 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-11 23:11 [PATCH tip/core/rcu 0/26] Torture-test updates for v5.14 Paul E. McKenney
2021-05-11 23:11 ` [PATCH tip/core/rcu 01/26] torture: Fix remaining erroneous torture.sh instance of $* Paul E. McKenney
2021-05-11 23:11 ` [PATCH tip/core/rcu 02/26] torture: Add "scenarios" option to kvm.sh --dryrun parameter Paul E. McKenney
2021-05-11 23:12 ` [PATCH tip/core/rcu 03/26] torture: Make kvm-again.sh use "scenarios" rather than "batches" file Paul E. McKenney
2021-05-11 23:12 ` [PATCH tip/core/rcu 04/26] refscale: Allow CPU hotplug to be enabled Paul E. McKenney
2021-05-11 23:12 ` [PATCH tip/core/rcu 05/26] rcuscale: " Paul E. McKenney
2021-05-11 23:12 ` [PATCH tip/core/rcu 06/26] torture: Add kvm-remote.sh script for distributed rcutorture test runs Paul E. McKenney
2021-05-11 23:12 ` [PATCH tip/core/rcu 07/26] refscale: Add acqrel, lock, and lock-irq Paul E. McKenney
2021-05-11 23:12 ` [PATCH tip/core/rcu 08/26] rcutorture: Abstract read-lock-held checks Paul E. McKenney
2021-05-11 23:12 ` [PATCH tip/core/rcu 09/26] torture: Fix grace-period rate output Paul E. McKenney
2021-05-11 23:12 ` [PATCH tip/core/rcu 10/26] torture: Abstract end-of-run summary Paul E. McKenney
2021-05-11 23:12 ` [PATCH tip/core/rcu 11/26] torture: Make kvm.sh use abstracted kvm-end-run-stats.sh Paul E. McKenney
2021-05-11 23:12 ` [PATCH tip/core/rcu 12/26] torture: Make the build machine control N in "make -jN" Paul E. McKenney
2021-05-11 23:12 ` [PATCH tip/core/rcu 13/26] torture: Make kvm-find-errors.sh account for kvm-remote.sh Paul E. McKenney
2021-05-11 23:12 ` [PATCH tip/core/rcu 14/26] rcutorture: Judge RCU priority boosting on grace periods, not callbacks Paul E. McKenney
2021-05-11 23:12 ` [PATCH tip/core/rcu 15/26] torture: Correctly fetch number of CPUs for non-English languages Paul E. McKenney
2021-05-11 23:12 ` [PATCH tip/core/rcu 16/26] torture: Set kvm.sh language to English Paul E. McKenney
2021-05-11 23:12 ` [PATCH tip/core/rcu 17/26] rcutorture: Delay-based false positives for RCU priority boosting tests Paul E. McKenney
2021-05-11 23:12 ` [PATCH tip/core/rcu 18/26] rcutorture: Consolidate rcu_torture_boost() timing and statistics Paul E. McKenney
2021-05-11 23:12 ` [PATCH tip/core/rcu 19/26] rcutorture: Make rcu_torture_boost_failed() check for GP end Paul E. McKenney
2021-05-11 23:12 ` [PATCH tip/core/rcu 20/26] rcutorture: Add BUSTED-BOOST to test RCU priority boosting tests Paul E. McKenney
2021-05-11 23:12 ` [PATCH tip/core/rcu 21/26] rcutorture: Forgive RCU boost failures when CPUs don't pass through QS Paul E. McKenney
2021-05-11 23:12 ` [PATCH tip/core/rcu 22/26] rcutorture: Don't count CPU-stalled time against priority boosting Paul E. McKenney
2021-05-11 23:12 ` [PATCH tip/core/rcu 23/26] torture: Make kvm-remote.sh account for network failure in pathname checks Paul E. McKenney
2021-05-11 23:12 ` [PATCH tip/core/rcu 24/26] torture: Don't cap remote runs by build-system number of CPUs Paul E. McKenney
2021-05-11 23:12 ` [PATCH tip/core/rcu 25/26] rcutorture: Move mem_dump_obj() tests into separate function Paul E. McKenney
2021-05-11 23:12 ` Paul E. McKenney [this message]
2021-05-11 23:23 ` [PATCH tip/core/rcu 01/10] kcsan: Add pointer to access-marking.txt to data_race() bullet Paul E. McKenney
2021-05-13 10:47 ` Akira Yokosawa
2021-05-13 10:53 ` Marco Elver
2021-05-13 17:50 ` Paul E. McKenney
2021-05-11 23:23 ` [PATCH tip/core/rcu 02/10] kcsan: Simplify value change detection Paul E. McKenney
2021-05-11 23:23 ` [PATCH tip/core/rcu 03/10] kcsan: Distinguish kcsan_report() calls Paul E. McKenney
2021-05-11 23:23 ` [PATCH tip/core/rcu 04/10] kcsan: Refactor passing watchpoint/other_info Paul E. McKenney
2021-05-11 23:23 ` [PATCH tip/core/rcu 05/10] kcsan: Fold panic() call into print_report() Paul E. McKenney
2021-05-11 23:23 ` [PATCH tip/core/rcu 06/10] kcsan: Refactor access_info initialization Paul E. McKenney
2021-05-11 23:23 ` [PATCH tip/core/rcu 07/10] kcsan: Remove reporting indirection Paul E. McKenney
2021-05-11 23:23 ` [PATCH tip/core/rcu 08/10] kcsan: Remove kcsan_report_type Paul E. McKenney
2021-05-11 23:24 ` [PATCH tip/core/rcu 09/10] kcsan: Report observed value changes Paul E. McKenney
2021-05-11 23:24 ` [PATCH tip/core/rcu 10/10] kcsan: Document "value changed" line Paul E. McKenney
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