[PATCH 09/14] workqueue: misc/cosmetic updates

Tejun Heo
2009-11-23T16:28:13Z

Make the following updates in preparation of concurrency managed
workqueue. None of these changes causes any visible behavior
difference.

* Add comments and adjust indentations to data structures and several
functions.

* Rename wq_per_cpu() to get_cwq() and swap the position of two
parameters for consistency. Convert a direct per_cpu_ptr() access
to wq->cpu_wq to get_cwq().

* Add work_static() and Update set_wq_data() such that it sets the
flags part to WORK_STRUCT_PENDING | WORK_STRUCT_STATIC if static |
@extra_flags.

* Move santiy check on work->entry emptiness from queue_work_on() to
__queue_work() which all queueing paths share.

* Make __queue_work() take @cpu and @wq instead of @cwq.

* Restructure flush_work() and __create_workqueue_key() to make them
easier to modify.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
include/linux/workqueue.h | 5 ++
kernel/workqueue.c | 127 +++++++++++++++++++++++++++++----------------
2 files changed, 88 insertions(+), 44 deletions(-)

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 0697946..ac06c55 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -96,9 +96,14 @@ struct execute_work {
#ifdef CONFIG_DEBUG_OBJECTS_WORK
extern void __init_work(struct work_struct *work, int onstack);
extern void destroy_work_on_stack(struct work_struct *work);
+static inline bool work_static(struct work_struct *work)
+{
+ return test_bit(WORK_STRUCT_STATIC, work_data_bits(work));
+}
#else
static inline void __init_work(struct work_struct *work, int onstack) { }
static inline void destroy_work_on_stack(struct work_struct *work) { }
+static inline bool work_static(struct work_struct *work) { return false; }
#endif

/*
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 3dccec6..e16c457 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -37,6 +37,16 @@
#include <trace/events/workqueue.h>

/*
+ * Structure fields follow one of the following exclusion rules.
+ *
+ * I: Set during initialization and read-only afterwards.
+ *
+ * L: cwq->lock protected. Access with cwq->lock held.
+ *
+ * W: workqueue_lock protected.
+ */
+
+/*
* The per-CPU workqueue (if single thread, we always use the first
* possible cpu).
*/
@@ -48,8 +58,8 @@ struct cpu_workqueue_struct {
wait_queue_head_t more_work;
struct work_struct *current_work;

- struct workqueue_struct *wq;
- struct task_struct *thread;
+ struct workqueue_struct *wq; /* I: the owning workqueue */
+ struct task_struct *thread;
} ____cacheline_aligned;

/*
@@ -57,13 +67,13 @@ struct cpu_workqueue_struct {
* per-CPU workqueues:
*/
struct workqueue_struct {
- struct cpu_workqueue_struct *cpu_wq;
- struct list_head list;
- const char *name;
+ struct cpu_workqueue_struct *cpu_wq; /* I: cwq's */
+ struct list_head list; /* W: list of all workqueues */
+ const char *name; /* I: workqueue name */
int singlethread;
int freezeable; /* Freeze threads during suspend */
#ifdef CONFIG_LOCKDEP
- struct lockdep_map lockdep_map;
+ struct lockdep_map lockdep_map;
#endif
};

@@ -204,8 +214,8 @@ static const struct cpumask *wq_cpu_map(struct workqueue_struct *wq)
? cpu_singlethread_map : cpu_populated_map;
}

-static
-struct cpu_workqueue_struct *wq_per_cpu(struct workqueue_struct *wq, int cpu)
+static struct cpu_workqueue_struct *get_cwq(unsigned int cpu,
+ struct workqueue_struct *wq)
{
if (unlikely(is_wq_single_threaded(wq)))
cpu = singlethread_cpu;
@@ -217,15 +227,14 @@ struct cpu_workqueue_struct *wq_per_cpu(struct workqueue_struct *wq, int cpu)
* - Must *only* be called if the pending flag is set
*/
static inline void set_wq_data(struct work_struct *work,
- struct cpu_workqueue_struct *cwq)
+ struct cpu_workqueue_struct *cwq,
+ unsigned long extra_flags)
{
- unsigned long new;
-
BUG_ON(!work_pending(work));

- new = (unsigned long) cwq | (1UL << WORK_STRUCT_PENDING);
- new |= WORK_STRUCT_FLAG_MASK & *work_data_bits(work);
- atomic_long_set(&work->data, new);
+ atomic_long_set(&work->data, (unsigned long)cwq |
+ (work_static(work) ? (1UL << WORK_STRUCT_STATIC) : 0) |
+ (1UL << WORK_STRUCT_PENDING) | extra_flags);
}

static inline
@@ -234,29 +243,47 @@ struct cpu_workqueue_struct *get_wq_data(struct work_struct *work)
return (void *) (atomic_long_read(&work->data) & WORK_STRUCT_WQ_DATA_MASK);
}

+/**
+ * insert_work - insert a work into cwq
+ * @cwq: cwq @work belongs to
+ * @work: work to insert
+ * @head: insertion point
+ * @extra_flags: extra WORK_STRUCT_* flags to set
+ *
+ * Insert @work into @cwq after @head.
+ *
+ * CONTEXT:
+ * spin_lock_irq(cwq->lock).
+ */
static void insert_work(struct cpu_workqueue_struct *cwq,
- struct work_struct *work, struct list_head *head)
+ struct work_struct *work, struct list_head *head,
+ unsigned int extra_flags)
{
trace_workqueue_insertion(cwq->thread, work);

- set_wq_data(work, cwq);
+ /* we own @work, set data and link */
+ set_wq_data(work, cwq, extra_flags);
+
/*
* Ensure that we get the right work->data if we see the
* result of list_add() below, see try_to_grab_pending().
*/
smp_wmb();
+
list_add_tail(&work->entry, head);
wake_up(&cwq->more_work);
}

-static void __queue_work(struct cpu_workqueue_struct *cwq,
+static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,
struct work_struct *work)
{
+ struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
unsigned long flags;

debug_work_activate(work);
spin_lock_irqsave(&cwq->lock, flags);
- insert_work(cwq, work, &cwq->worklist);
+ BUG_ON(!list_empty(&work->entry));
+ insert_work(cwq, work, &cwq->worklist, 0);
spin_unlock_irqrestore(&cwq->lock, flags);
}

@@ -298,8 +325,7 @@ queue_work_on(int cpu, struct workqueue_struct *wq, struct work_struct *work)
int ret = 0;

if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work))) {
- BUG_ON(!list_empty(&work->entry));
- __queue_work(wq_per_cpu(wq, cpu), work);
+ __queue_work(cpu, wq, work);
ret = 1;
}
return ret;
@@ -310,9 +336,8 @@ static void delayed_work_timer_fn(unsigned long __data)
{
struct delayed_work *dwork = (struct delayed_work *)__data;
struct cpu_workqueue_struct *cwq = get_wq_data(&dwork->work);
- struct workqueue_struct *wq = cwq->wq;

- __queue_work(wq_per_cpu(wq, smp_processor_id()), &dwork->work);
+ __queue_work(smp_processor_id(), cwq->wq, &dwork->work);
}

/**
@@ -356,7 +381,7 @@ int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
timer_stats_timer_set_start_info(&dwork->timer);

/* This stores cwq for the moment, for the timer_fn */
- set_wq_data(work, wq_per_cpu(wq, raw_smp_processor_id()));
+ set_wq_data(work, get_cwq(raw_smp_processor_id(), wq), 0);
timer->expires = jiffies + delay;
timer->data = (unsigned long)dwork;
timer->function = delayed_work_timer_fn;
@@ -420,6 +445,12 @@ static void run_workqueue(struct cpu_workqueue_struct *cwq)
spin_unlock_irq(&cwq->lock);
}

+/**
+ * worker_thread - the worker thread function
+ * @__cwq: cwq to serve
+ *
+ * The cwq worker thread function.
+ */
static int worker_thread(void *__cwq)
{
struct cpu_workqueue_struct *cwq = __cwq;
@@ -458,6 +489,17 @@ static void wq_barrier_func(struct work_struct *work)
complete(&barr->done);
}

+/**
+ * insert_wq_barrier - insert a barrier work
+ * @cwq: cwq to insert barrier into
+ * @barr: wq_barrier to insert
+ * @head: insertion point
+ *
+ * Insert barrier @barr into @cwq before @head.
+ *
+ * CONTEXT:
+ * spin_lock_irq(cwq->lock).
+ */
static void insert_wq_barrier(struct cpu_workqueue_struct *cwq,
struct wq_barrier *barr, struct list_head *head)
{
@@ -469,11 +511,10 @@ static void insert_wq_barrier(struct cpu_workqueue_struct *cwq,
*/
INIT_WORK_ON_STACK(&barr->work, wq_barrier_func);
__set_bit(WORK_STRUCT_PENDING, work_data_bits(&barr->work));
-
init_completion(&barr->done);

debug_work_activate(&barr->work);
- insert_work(cwq, &barr->work, head);
+ insert_work(cwq, &barr->work, head, 0);
}

static int flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
@@ -507,9 +548,6 @@ static int flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
*
* We sleep until all works which were queued on entry have been handled,
* but we are not livelocked by new incoming ones.
- *
- * This function used to run the workqueues itself. Now we just wait for the
- * helper threads to do it.
*/
void flush_workqueue(struct workqueue_struct *wq)
{
@@ -548,7 +586,6 @@ int flush_work(struct work_struct *work)
lock_map_acquire(&cwq->wq->lockdep_map);
lock_map_release(&cwq->wq->lockdep_map);

- prev = NULL;
spin_lock_irq(&cwq->lock);
if (!list_empty(&work->entry)) {
/*
@@ -557,22 +594,22 @@ int flush_work(struct work_struct *work)
*/
smp_rmb();
if (unlikely(cwq != get_wq_data(work)))
- goto out;
+ goto already_gone;
prev = &work->entry;
} else {
if (cwq->current_work != work)
- goto out;
+ goto already_gone;
prev = &cwq->worklist;
}
insert_wq_barrier(cwq, &barr, prev->next);
-out:
- spin_unlock_irq(&cwq->lock);
- if (!prev)
- return 0;

+ spin_unlock_irq(&cwq->lock);
wait_for_completion(&barr.done);
destroy_work_on_stack(&barr.work);
return 1;
+already_gone:
+ spin_unlock_irq(&cwq->lock);
+ return 0;
}
EXPORT_SYMBOL_GPL(flush_work);

@@ -655,7 +692,7 @@ static void wait_on_work(struct work_struct *work)
cpu_map = wq_cpu_map(wq);

for_each_cpu(cpu, cpu_map)
- wait_on_cpu_work(per_cpu_ptr(wq->cpu_wq, cpu), work);
+ wait_on_cpu_work(get_cwq(cpu, wq), work);
}

static int __cancel_work_timer(struct work_struct *work,
@@ -772,9 +809,7 @@ EXPORT_SYMBOL(schedule_delayed_work);
void flush_delayed_work(struct delayed_work *dwork)
{
if (del_timer_sync(&dwork->timer)) {
- struct cpu_workqueue_struct *cwq;
- cwq = wq_per_cpu(keventd_wq, get_cpu());
- __queue_work(cwq, &dwork->work);
+ __queue_work(get_cpu(), keventd_wq, &dwork->work);
put_cpu();
}
flush_work(&dwork->work);
@@ -957,13 +992,11 @@ struct workqueue_struct *__create_workqueue_key(const char *name,

wq = kzalloc(sizeof(*wq), GFP_KERNEL);
if (!wq)
- return NULL;
+ goto err;

wq->cpu_wq = alloc_percpu(struct cpu_workqueue_struct);
- if (!wq->cpu_wq) {
- kfree(wq);
- return NULL;
- }
+ if (!wq->cpu_wq)
+ goto err;

wq->name = name;
lockdep_init_map(&wq->lockdep_map, lock_name, key, 0);
@@ -1007,6 +1040,12 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
wq = NULL;
}
return wq;
+err:
+ if (wq) {
+ free_percpu(wq->cpu_wq);
+ kfree(wq);
+ }
+ return NULL;
}
EXPORT_SYMBOL_GPL(__create_workqueue_key);

--
1.6.5.3