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Date: Sun, 29 Jun 2008 20:51:31 +0400
From: Oleg Nesterov <oleg@...sign.ru>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Gautham R Shenoy <ego@...ibm.com>,
Heiko Carstens <heiko.carstens@...ibm.com>,
Max Krasnyansky <maxk@...lcomm.com>, Paul Jackson <pj@....com>,
Paul Menage <menage@...gle.com>,
Peter Zijlstra <peterz@...radead.org>,
Vegard Nossum <vegard.nossum@...il.com>,
linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] workqueues: make get_online_cpus() useable for work->func()
workqueue_cpu_callback(CPU_DEAD) flushes cwq->thread under
cpu_maps_update_begin(). This means that the multithreaded workqueues can't
use get_online_cpus() due to the possible deadlock, very bad and very old
problem.
Introduce the new state, CPU_POST_DEAD, which is called after
cpu_hotplug_done() but before cpu_maps_update_done().
Change workqueue_cpu_callback() to use CPU_POST_DEAD instead of CPU_DEAD.
This means that create/destroy functions can't rely on get_online_cpus()
any longer and should take cpu_add_remove_lock instead.
Signed-off-by: Oleg Nesterov <oleg@...sign.ru>
include/linux/notifier.h | 2 ++
kernel/cpu.c | 5 +++++
kernel/workqueue.c | 18 +++++++++---------
3 files changed, 16 insertions(+), 9 deletions(-)
--- 26-rc2/include/linux/notifier.h~WQ_4_GET_ONLINE_CPUS 2008-05-18 15:44:16.000000000 +0400
+++ 26-rc2/include/linux/notifier.h 2008-05-18 15:44:16.000000000 +0400
@@ -213,6 +213,8 @@ static inline int notifier_to_errno(int
#define CPU_DEAD 0x0007 /* CPU (unsigned)v dead */
#define CPU_DYING 0x0008 /* CPU (unsigned)v not running any task,
* not handling interrupts, soon dead */
+#define CPU_POST_DEAD 0x0009 /* CPU (unsigned)v dead, cpu_hotplug
+ * lock is dropped */
/* Used for CPU hotplug events occuring while tasks are frozen due to a suspend
* operation in progress
--- 26-rc2/kernel/cpu.c~WQ_4_GET_ONLINE_CPUS 2008-05-18 15:44:18.000000000 +0400
+++ 26-rc2/kernel/cpu.c 2008-06-29 20:03:19.000000000 +0400
@@ -261,6 +261,11 @@ out_allowed:
set_cpus_allowed_ptr(current, &old_allowed);
out_release:
cpu_hotplug_done();
+ if (!err) {
+ if (raw_notifier_call_chain(&cpu_chain, CPU_POST_DEAD | mod,
+ hcpu) == NOTIFY_BAD)
+ BUG();
+ }
return err;
}
--- 26-rc2/kernel/workqueue.c~WQ_4_GET_ONLINE_CPUS 2008-06-29 18:34:06.000000000 +0400
+++ 26-rc2/kernel/workqueue.c 2008-06-29 19:36:27.000000000 +0400
@@ -791,7 +791,7 @@ struct workqueue_struct *__create_workqu
err = create_workqueue_thread(cwq, singlethread_cpu);
start_workqueue_thread(cwq, -1);
} else {
- get_online_cpus();
+ cpu_maps_update_begin();
spin_lock(&workqueue_lock);
list_add(&wq->list, &workqueues);
spin_unlock(&workqueue_lock);
@@ -803,7 +803,7 @@ struct workqueue_struct *__create_workqu
err = create_workqueue_thread(cwq, cpu);
start_workqueue_thread(cwq, cpu);
}
- put_online_cpus();
+ cpu_maps_update_done();
}
if (err) {
@@ -817,8 +817,8 @@ EXPORT_SYMBOL_GPL(__create_workqueue_key
static void cleanup_workqueue_thread(struct cpu_workqueue_struct *cwq)
{
/*
- * Our caller is either destroy_workqueue() or CPU_DEAD,
- * get_online_cpus() protects cwq->thread.
+ * Our caller is either destroy_workqueue() or CPU_POST_DEAD,
+ * cpu_add_remove_lock protects cwq->thread.
*/
if (cwq->thread == NULL)
return;
@@ -828,7 +828,7 @@ static void cleanup_workqueue_thread(str
flush_cpu_workqueue(cwq);
/*
- * If the caller is CPU_DEAD and cwq->worklist was not empty,
+ * If the caller is CPU_POST_DEAD and cwq->worklist was not empty,
* a concurrent flush_workqueue() can insert a barrier after us.
* However, in that case run_workqueue() won't return and check
* kthread_should_stop() until it flushes all work_struct's.
@@ -852,14 +852,14 @@ void destroy_workqueue(struct workqueue_
const cpumask_t *cpu_map = wq_cpu_map(wq);
int cpu;
- get_online_cpus();
+ cpu_maps_update_begin();
spin_lock(&workqueue_lock);
list_del(&wq->list);
spin_unlock(&workqueue_lock);
for_each_cpu_mask(cpu, *cpu_map)
cleanup_workqueue_thread(per_cpu_ptr(wq->cpu_wq, cpu));
- put_online_cpus();
+ cpu_maps_update_done();
free_percpu(wq->cpu_wq);
kfree(wq);
@@ -898,7 +898,7 @@ static int __devinit workqueue_cpu_callb
case CPU_UP_CANCELED:
start_workqueue_thread(cwq, -1);
- case CPU_DEAD:
+ case CPU_POST_DEAD:
cleanup_workqueue_thread(cwq);
break;
}
@@ -906,7 +906,7 @@ static int __devinit workqueue_cpu_callb
switch (action) {
case CPU_UP_CANCELED:
- case CPU_DEAD:
+ case CPU_POST_DEAD:
cpu_clear(cpu, cpu_populated_map);
}
--
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