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Koen Kooi
56e60917b2
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net> Signed-off-by: Denys Dmytriyenko <denys@ti.com> Signed-off-by: Denys Dmytriyenko <denis@denix.org>
121 lines
4.1 KiB
Diff
121 lines
4.1 KiB
Diff
From 47ba7731c120a3ed09336d18b85493bd85d926f2 Mon Sep 17 00:00:00 2001
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From: Tejun Heo <tj@kernel.org>
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Date: Tue, 17 Jul 2012 12:39:26 -0700
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Subject: [PATCH 47/73] workqueue: perform cpu down operations from low
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priority cpu_notifier()
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commit 6575820221f7a4dd6eadecf7bf83cdd154335eda upstream.
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Currently, all workqueue cpu hotplug operations run off
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CPU_PRI_WORKQUEUE which is higher than normal notifiers. This is to
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ensure that workqueue is up and running while bringing up a CPU before
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other notifiers try to use workqueue on the CPU.
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Per-cpu workqueues are supposed to remain working and bound to the CPU
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for normal CPU_DOWN_PREPARE notifiers. This holds mostly true even
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with workqueue offlining running with higher priority because
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workqueue CPU_DOWN_PREPARE only creates a bound trustee thread which
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runs the per-cpu workqueue without concurrency management without
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explicitly detaching the existing workers.
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However, if the trustee needs to create new workers, it creates
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unbound workers which may wander off to other CPUs while
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CPU_DOWN_PREPARE notifiers are in progress. Furthermore, if the CPU
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down is cancelled, the per-CPU workqueue may end up with workers which
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aren't bound to the CPU.
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While reliably reproducible with a convoluted artificial test-case
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involving scheduling and flushing CPU burning work items from CPU down
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notifiers, this isn't very likely to happen in the wild, and, even
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when it happens, the effects are likely to be hidden by the following
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successful CPU down.
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Fix it by using different priorities for up and down notifiers - high
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priority for up operations and low priority for down operations.
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Workqueue cpu hotplug operations will soon go through further cleanup.
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Signed-off-by: Tejun Heo <tj@kernel.org>
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Acked-by: "Rafael J. Wysocki" <rjw@sisk.pl>
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Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
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---
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include/linux/cpu.h | 5 +++--
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kernel/workqueue.c | 38 +++++++++++++++++++++++++++++++++++++-
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2 files changed, 40 insertions(+), 3 deletions(-)
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diff --git a/include/linux/cpu.h b/include/linux/cpu.h
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index 6cb60fd..c692acc 100644
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--- a/include/linux/cpu.h
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+++ b/include/linux/cpu.h
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@@ -66,8 +66,9 @@ enum {
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/* migration should happen before other stuff but after perf */
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CPU_PRI_PERF = 20,
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CPU_PRI_MIGRATION = 10,
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- /* prepare workqueues for other notifiers */
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- CPU_PRI_WORKQUEUE = 5,
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+ /* bring up workqueues before normal notifiers and down after */
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+ CPU_PRI_WORKQUEUE_UP = 5,
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+ CPU_PRI_WORKQUEUE_DOWN = -5,
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};
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#define CPU_ONLINE 0x0002 /* CPU (unsigned)v is up */
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diff --git a/kernel/workqueue.c b/kernel/workqueue.c
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index 7947e16..a650bee 100644
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--- a/kernel/workqueue.c
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+++ b/kernel/workqueue.c
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@@ -3586,6 +3586,41 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
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return notifier_from_errno(0);
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}
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+/*
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+ * Workqueues should be brought up before normal priority CPU notifiers.
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+ * This will be registered high priority CPU notifier.
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+ */
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+static int __devinit workqueue_cpu_up_callback(struct notifier_block *nfb,
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+ unsigned long action,
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+ void *hcpu)
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+{
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+ switch (action & ~CPU_TASKS_FROZEN) {
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+ case CPU_UP_PREPARE:
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+ case CPU_UP_CANCELED:
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+ case CPU_DOWN_FAILED:
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+ case CPU_ONLINE:
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+ return workqueue_cpu_callback(nfb, action, hcpu);
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+ }
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+ return NOTIFY_OK;
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+}
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+
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+/*
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+ * Workqueues should be brought down after normal priority CPU notifiers.
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+ * This will be registered as low priority CPU notifier.
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+ */
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+static int __devinit workqueue_cpu_down_callback(struct notifier_block *nfb,
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+ unsigned long action,
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+ void *hcpu)
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+{
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+ switch (action & ~CPU_TASKS_FROZEN) {
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+ case CPU_DOWN_PREPARE:
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+ case CPU_DYING:
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+ case CPU_POST_DEAD:
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+ return workqueue_cpu_callback(nfb, action, hcpu);
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+ }
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+ return NOTIFY_OK;
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+}
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+
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#ifdef CONFIG_SMP
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struct work_for_cpu {
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@@ -3779,7 +3814,8 @@ static int __init init_workqueues(void)
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unsigned int cpu;
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int i;
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- cpu_notifier(workqueue_cpu_callback, CPU_PRI_WORKQUEUE);
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+ cpu_notifier(workqueue_cpu_up_callback, CPU_PRI_WORKQUEUE_UP);
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+ cpu_notifier(workqueue_cpu_down_callback, CPU_PRI_WORKQUEUE_DOWN);
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/* initialize gcwqs */
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for_each_gcwq_cpu(cpu) {
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--
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1.7.7.6
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