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Subject[PATCH V2 01/15] workqueue: add lock_work_pool()
Date
get_work_pool() is too weak, the caller *always* has to lock and check.
We merge all the code and name it lock_work_pool() and remove get_work_pool().

This patch has a little overhead for __queue_work() and try_to_grab_pending():
Even worker_pool_by_id(pool_id) == get_cwq(cpu, wq)->pool,
It will still look up the worker.
But this lookup is neeeded in later patches.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
kernel/workqueue.c | 170 ++++++++++++++++++++++++++++-----------------------
1 files changed, 93 insertions(+), 77 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index ea7f696..f90d0bd 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -516,10 +516,8 @@ static int work_next_color(int color)
* work->data. These functions should only be called while the work is
* owned - ie. while the PENDING bit is set.
*
- * get_work_pool() and get_work_cwq() can be used to obtain the pool or cwq
- * corresponding to a work. Pool is available once the work has been
- * queued anywhere after initialization until it is sync canceled. cwq is
- * available only while the work item is queued.
+ * get_work_cwq() can be used to obtain the cwq corresponding to a work.
+ * It is available only while the work item is queued.
*
* %WORK_OFFQ_CANCELING is used to mark a work item which is being
* canceled. While being canceled, a work item may have its PENDING set
@@ -578,31 +576,6 @@ static struct cpu_workqueue_struct *get_work_cwq(struct work_struct *work)
}

/**
- * get_work_pool - return the worker_pool a given work was associated with
- * @work: the work item of interest
- *
- * Return the worker_pool @work was last associated with. %NULL if none.
- */
-static struct worker_pool *get_work_pool(struct work_struct *work)
-{
- unsigned long data = atomic_long_read(&work->data);
- struct worker_pool *pool;
- int pool_id;
-
- if (data & WORK_STRUCT_CWQ)
- return ((struct cpu_workqueue_struct *)
- (data & WORK_STRUCT_WQ_DATA_MASK))->pool;
-
- pool_id = data >> WORK_OFFQ_POOL_SHIFT;
- if (pool_id == WORK_OFFQ_POOL_NONE)
- return NULL;
-
- pool = worker_pool_by_id(pool_id);
- WARN_ON_ONCE(!pool);
- return pool;
-}
-
-/**
* get_work_pool_id - return the worker pool ID a given work is associated with
* @work: the work item of interest
*
@@ -921,6 +894,64 @@ static struct worker *find_worker_executing_work(struct worker_pool *pool,
}

/**
+ * lock_work_pool - return and lock the pool a given work was associated with
+ * @work: the work item of interest
+ * @queued_cwq: set to the queued cwq if the work is still queued
+ * @running_worker: set to the running worker if the work is still running
+ *
+ * CONTEXT:
+ * local_irq_disable().
+ *
+ * Return the worker_pool @work was last associated with. %NULL if none.
+ */
+
+static
+struct worker_pool *lock_work_pool(struct work_struct *work,
+ struct cpu_workqueue_struct **queued_cwq,
+ struct worker **running_worker)
+{
+ unsigned long data = atomic_long_read(&work->data);
+ unsigned long pool_id;
+ struct worker_pool *pool;
+ struct cpu_workqueue_struct *cwq;
+ struct worker *worker = NULL;
+
+ if (data & WORK_STRUCT_CWQ) {
+ cwq = (void *)(data & WORK_STRUCT_WQ_DATA_MASK);
+ pool = cwq->pool;
+ spin_lock(&pool->lock);
+ /*
+ * work->data is guaranteed to point to cwq only while the work
+ * item is queued on cwq->wq, and both updating work->data to
+ * point to cwq on queueing and to pool on dequeueing are done
+ * under cwq->pool->lock. This in turn guarantees that,
+ * if work->data points to cwq which is associated with a
+ * locked pool, the work item is currently queued on that pool.
+ */
+ cwq = get_work_cwq(work);
+ if (cwq && cwq->pool == pool) {
+ *queued_cwq = cwq;
+ worker = find_worker_executing_work(pool, work);
+ }
+ } else {
+ pool_id = data >> WORK_OFFQ_POOL_SHIFT;
+ if (pool_id == WORK_OFFQ_POOL_NONE)
+ return NULL;
+
+ pool = worker_pool_by_id(pool_id);
+ if (!pool)
+ return NULL;
+
+ spin_lock(&pool->lock);
+ worker = find_worker_executing_work(pool, work);
+ }
+
+ if (worker)
+ *running_worker = worker;
+ return pool;
+}
+
+/**
* move_linked_works - move linked works to a list
* @work: start of series of works to be scheduled
* @head: target list to append @work to
@@ -1053,7 +1084,8 @@ static int try_to_grab_pending(struct work_struct *work, bool is_dwork,
unsigned long *flags)
{
struct worker_pool *pool;
- struct cpu_workqueue_struct *cwq;
+ struct cpu_workqueue_struct *cwq = NULL;
+ struct worker *worker = NULL;

local_irq_save(*flags);

@@ -1078,21 +1110,11 @@ static int try_to_grab_pending(struct work_struct *work, bool is_dwork,
* The queueing is in progress, or it is already queued. Try to
* steal it from ->worklist without clearing WORK_STRUCT_PENDING.
*/
- pool = get_work_pool(work);
+ pool = lock_work_pool(work, &cwq, &worker);
if (!pool)
goto fail;

- spin_lock(&pool->lock);
- /*
- * work->data is guaranteed to point to cwq only while the work
- * item is queued on cwq->wq, and both updating work->data to point
- * to cwq on queueing and to pool on dequeueing are done under
- * cwq->pool->lock. This in turn guarantees that, if work->data
- * points to cwq which is associated with a locked pool, the work
- * item is currently queued on that pool.
- */
- cwq = get_work_cwq(work);
- if (cwq && cwq->pool == pool) {
+ if (cwq) {
debug_work_deactivate(work);

/*
@@ -1199,34 +1221,27 @@ static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,
/* determine the cwq to use */
if (!(wq->flags & WQ_UNBOUND)) {
struct worker_pool *last_pool;
+ struct worker *worker = NULL;
+ struct cpu_workqueue_struct *dummy_cwq;

if (cpu == WORK_CPU_UNBOUND)
cpu = raw_smp_processor_id();

/*
* It's multi cpu. If @work was previously on a different
- * cpu, it might still be running there, in which case the
- * work needs to be queued on that cpu to guarantee
+ * pool, it might still be running there, in which case the
+ * work needs to be queued on that pool to guarantee
* non-reentrancy.
*/
cwq = get_cwq(cpu, wq);
- last_pool = get_work_pool(work);
-
- if (last_pool && last_pool != cwq->pool) {
- struct worker *worker;
-
- spin_lock(&last_pool->lock);
-
- worker = find_worker_executing_work(last_pool, work);
+ last_pool = lock_work_pool(work, &dummy_cwq, &worker);

- if (worker && worker->current_cwq->wq == wq) {
- cwq = get_cwq(last_pool->cpu, wq);
- } else {
- /* meh... not running there, queue here */
+ if (worker && worker->current_cwq->wq == wq) {
+ cwq = get_cwq(last_pool->cpu, wq);
+ } else if (cwq->pool != last_pool) {
+ /* meh... not running there, queue here */
+ if (last_pool)
spin_unlock(&last_pool->lock);
- spin_lock(&cwq->pool->lock);
- }
- } else {
spin_lock(&cwq->pool->lock);
}
} else {
@@ -2749,25 +2764,22 @@ static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr)
{
struct worker *worker = NULL;
struct worker_pool *pool;
- struct cpu_workqueue_struct *cwq;
+ struct cpu_workqueue_struct *cwq = NULL;

might_sleep();
- pool = get_work_pool(work);
- if (!pool)
+ local_irq_disable();
+ pool = lock_work_pool(work, &cwq, &worker);
+ if (!pool) {
+ local_irq_enable();
return false;
+ }

- spin_lock_irq(&pool->lock);
- /* see the comment in try_to_grab_pending() with the same code */
- cwq = get_work_cwq(work);
- if (cwq) {
- if (unlikely(cwq->pool != pool))
- goto already_gone;
- } else {
- worker = find_worker_executing_work(pool, work);
- if (!worker)
- goto already_gone;
+ if (cwq)
+ worker = NULL;
+ else if (worker)
cwq = worker->current_cwq;
- }
+ else
+ goto already_gone;

insert_wq_barrier(cwq, barr, work, worker);
spin_unlock_irq(&pool->lock);
@@ -3386,19 +3398,23 @@ EXPORT_SYMBOL_GPL(workqueue_congested);
*/
unsigned int work_busy(struct work_struct *work)
{
- struct worker_pool *pool = get_work_pool(work);
+ struct worker_pool *pool;
+ struct cpu_workqueue_struct *cwq = NULL;
+ struct worker *worker = NULL;
unsigned long flags;
unsigned int ret = 0;

if (work_pending(work))
ret |= WORK_BUSY_PENDING;

+ local_irq_save(flags);
+ pool = lock_work_pool(work, &cwq, &worker);
if (pool) {
- spin_lock_irqsave(&pool->lock, flags);
- if (find_worker_executing_work(pool, work))
+ if (worker)
ret |= WORK_BUSY_RUNNING;
- spin_unlock_irqrestore(&pool->lock, flags);
+ spin_unlock(&pool->lock);
}
+ local_irq_restore(flags);

return ret;
}
--
1.7.7.6


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