From: "Paul E. McKenney" <paulmck@linux.ibm.com>
To: linux-kernel@vger.kernel.org
Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.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@linux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 01/14] rcu: Stop expedited grace periods from relying on stop-machine
Date: Sun, 11 Nov 2018 11:28:51 -0800 [thread overview]
Message-ID: <20181111192904.3199-1-paulmck@linux.ibm.com> (raw)
In-Reply-To: <20181111192839.GA32144@linux.ibm.com>
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
The CPU-selection code in sync_rcu_exp_select_cpus() disables preemption
to prevent the cpu_online_mask from changing. However, this relies on
the stop-machine mechanism in the CPU-hotplug offline code, which is not
desirable (it would be good to someday remove the stop-machine mechanism).
This commit therefore instead uses the relevant leaf rcu_node structure's
->ffmask, which has a bit set for all CPUs that are fully functional.
A given CPU's bit is cleared very early during offline processing by
rcutree_offline_cpu() and set very late during online processing by
rcutree_online_cpu(). Therefore, if a CPU's bit is set in this mask, and
preemption is disabled, we have to be before the synchronize_sched() in
the CPU-hotplug offline code, which means that the CPU is guaranteed to be
workqueue-ready throughout the duration of the enclosing preempt_disable()
region of code.
This also has the side-effect of using WORK_CPU_UNBOUND if all the CPUs for
this leaf rcu_node structure are offline, which is an acceptable difference
in behavior.
Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
kernel/rcu/tree_exp.h | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 8d18c1014e2b..e669ccf3751b 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -450,10 +450,12 @@ static void sync_rcu_exp_select_cpus(smp_call_func_t func)
}
INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
preempt_disable();
- cpu = cpumask_next(rnp->grplo - 1, cpu_online_mask);
+ cpu = find_next_bit(&rnp->ffmask, BITS_PER_LONG, -1);
/* If all offline, queue the work on an unbound CPU. */
- if (unlikely(cpu > rnp->grphi))
+ if (unlikely(cpu > rnp->grphi - rnp->grplo))
cpu = WORK_CPU_UNBOUND;
+ else
+ cpu += rnp->grplo;
queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work);
preempt_enable();
rnp->exp_need_flush = true;
--
2.17.1
next prev parent reply other threads:[~2018-11-11 19:29 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-11 19:28 [PATCH tip/core/rcu 0/14] Miscellaneous fixes for v4.21/v5.0 Paul E. McKenney
2018-11-11 19:28 ` Paul E. McKenney [this message]
2018-11-11 19:28 ` [PATCH tip/core/rcu 02/14] MAINTAINERS: Update from @linux.vnet.ibm.com to @linux.ibm.com Paul E. McKenney
2018-11-11 19:28 ` [PATCH tip/core/rcu 03/14] rcu: Avoid double multiply by HZ Paul E. McKenney
2018-11-11 19:28 ` [PATCH tip/core/rcu 04/14] rcu: Parameterize rcu_check_gp_start_stall() Paul E. McKenney
2018-11-11 19:28 ` [PATCH tip/core/rcu 05/14] rcu: Add state name to show_rcu_gp_kthreads() output Paul E. McKenney
2018-11-11 19:28 ` [PATCH tip/core/rcu 06/14] rcu: Add jiffies-since-GP-activity to show_rcu_gp_kthreads() Paul E. McKenney
2018-11-11 19:28 ` [PATCH tip/core/rcu 07/14] rcu: Adjust the comment of function rcu_is_watching Paul E. McKenney
2018-11-11 19:28 ` [PATCH tip/core/rcu 08/14] rcu: Trace end of grace period before end of grace period Paul E. McKenney
2018-11-11 19:28 ` [PATCH tip/core/rcu 09/14] rcu: Speed up expedited GPs when interrupting RCU reader Paul E. McKenney
2018-11-11 19:29 ` [PATCH tip/core/rcu 10/14] rcu: Replace this_cpu_ptr() with __this_cpu_read() Paul E. McKenney
2018-11-11 19:29 ` [PATCH tip/core/rcu 11/14] rcu: Avoid signed integer overflow in rcu_preempt_deferred_qs() Paul E. McKenney
2018-11-11 19:29 ` [PATCH tip/core/rcu 12/14] MAINTAINERS: Add Joel Fernandes as RCU reviewer Paul E. McKenney
2018-11-11 19:29 ` [PATCH tip/core/rcu 13/14] checkpatch: Create table of obsolete APIs and apply to RCU Paul E. McKenney
2018-11-11 19:29 ` [PATCH tip/core/rcu 14/14] checkpatch.pl: Suggest lockdep instead of asserting !spin_is_locked() Paul E. McKenney
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