The patch titled
workqueues: make get_online_cpus() useable for work->func()
has been removed from the -mm tree. Its filename was
workqueues-make-get_online_cpus-useable-for-work-func.patch
This patch was dropped because it was merged into mainline or a subsystem tree
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: workqueues: make get_online_cpus() useable for work->func()
From: Oleg Nesterov <oleg@xxxxxxxxxx>
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.
[akpm@xxxxxxxxxxxxxxxxxxxx: fix CONFIG_SMP=n]
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Acked-by: Gautham R Shenoy <ego@xxxxxxxxxx>
Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Cc: Max Krasnyansky <maxk@xxxxxxxxxxxx>
Cc: Paul Jackson <pj@xxxxxxx>
Cc: Paul Menage <menage@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Vegard Nossum <vegard.nossum@xxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/cpu.h | 15 +++++++++++----
include/linux/notifier.h | 2 ++
kernel/cpu.c | 5 +++++
kernel/workqueue.c | 18 +++++++++---------
4 files changed, 27 insertions(+), 13 deletions(-)
diff -puN include/linux/cpu.h~workqueues-make-get_online_cpus-useable-for-work-func include/linux/cpu.h
--- a/include/linux/cpu.h~workqueues-make-get_online_cpus-useable-for-work-func
+++ a/include/linux/cpu.h
@@ -69,10 +69,11 @@ static inline void unregister_cpu_notifi
#endif
int cpu_up(unsigned int cpu);
-
extern void cpu_hotplug_init(void);
+extern void cpu_maps_update_begin(void);
+extern void cpu_maps_update_done(void);
-#else
+#else /* CONFIG_SMP */
static inline int register_cpu_notifier(struct notifier_block *nb)
{
@@ -87,10 +88,16 @@ static inline void cpu_hotplug_init(void
{
}
+static inline void cpu_maps_update_begin(void)
+{
+}
+
+static inline void cpu_maps_update_done(void)
+{
+}
+
#endif /* CONFIG_SMP */
extern struct sysdev_class cpu_sysdev_class;
-extern void cpu_maps_update_begin(void);
-extern void cpu_maps_update_done(void);
#ifdef CONFIG_HOTPLUG_CPU
/* Stop CPUs going up and down. */
diff -puN include/linux/notifier.h~workqueues-make-get_online_cpus-useable-for-work-func include/linux/notifier.h
--- a/include/linux/notifier.h~workqueues-make-get_online_cpus-useable-for-work-func
+++ a/include/linux/notifier.h
@@ -214,6 +214,8 @@ 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
diff -puN kernel/cpu.c~workqueues-make-get_online_cpus-useable-for-work-func kernel/cpu.c
--- a/kernel/cpu.c~workqueues-make-get_online_cpus-useable-for-work-func
+++ a/kernel/cpu.c
@@ -285,6 +285,11 @@ 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;
}
diff -puN kernel/workqueue.c~workqueues-make-get_online_cpus-useable-for-work-func kernel/workqueue.c
--- a/kernel/workqueue.c~workqueues-make-get_online_cpus-useable-for-work-func
+++ a/kernel/workqueue.c
@@ -828,7 +828,7 @@ 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);
@@ -840,7 +840,7 @@ 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) {
@@ -854,8 +854,8 @@ 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;
@@ -865,7 +865,7 @@ 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.
@@ -889,14 +889,14 @@ 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_nr(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);
@@ -935,7 +935,7 @@ 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;
}
@@ -943,7 +943,7 @@ 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);
}
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
origin.patch
linux-next.patch
migrate_timers-add-comment-use-spinlock_irq.patch
tracehook-add-linux-tracehookh.patch
tracehook-exec.patch
tracehook-unexport-ptrace_notify.patch
tracehook-exit.patch
tracehook-clone.patch
tracehook-vfork-done.patch
tracehook-release_task.patch
tracehook-tracehook_tracer_task.patch
tracehook-tracehook_expect_breakpoints.patch
tracehook-tracehook_signal_handler.patch
tracehook-tracehook_consider_ignored_signal.patch
tracehook-tracehook_consider_fatal_signal.patch
tracehook-syscall.patch
tracehook-get_signal_to_deliver.patch
tracehook-job-control.patch
tracehook-death.patch
tracehook-force-signal_pending.patch
tracehook-tif_notify_resume.patch
tracehook-asm-syscallh.patch
tracehook-config_have_arch_tracehook.patch
tracehook-wait_task_inactive.patch
task_current_syscall.patch
proc-pid-syscall.patch
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