diff options
| -rw-r--r-- | Documentation/slow-work.txt | 12 | ||||
| -rw-r--r-- | include/linux/slow-work.h | 2 | ||||
| -rw-r--r-- | kernel/slow-work.c | 81 |
3 files changed, 88 insertions, 7 deletions
diff --git a/Documentation/slow-work.txt b/Documentation/slow-work.txt index c655c51..2e384bd 100644 --- a/Documentation/slow-work.txt +++ b/Documentation/slow-work.txt @@ -108,7 +108,17 @@ on the item, 0 otherwise. The items are reference counted, so there ought to be no need for a flush -operation. When all a module's slow work items have been processed, and the +operation. But as the reference counting is optional, means to cancel +existing work items are also included: + + cancel_slow_work(&myitem); + +can be used to cancel pending work. The above cancel function waits for +existing work to have been executed (or prevent execution of them, depending +on timing). + + +When all a module's slow work items have been processed, and the module has no further interest in the facility, it should unregister its interest: diff --git a/include/linux/slow-work.h b/include/linux/slow-work.h index 9adb2b3..eef2018 100644 --- a/include/linux/slow-work.h +++ b/include/linux/slow-work.h @@ -51,6 +51,7 @@ struct slow_work { #define SLOW_WORK_EXECUTING 1 /* item currently executing */ #define SLOW_WORK_ENQ_DEFERRED 2 /* item enqueue deferred */ #define SLOW_WORK_VERY_SLOW 3 /* item is very slow */ +#define SLOW_WORK_CANCELLING 4 /* item is being cancelled, don't enqueue */ const struct slow_work_ops *ops; /* operations table for this item */ struct list_head link; /* link in queue */ }; @@ -88,6 +89,7 @@ static inline void vslow_work_init(struct slow_work *work, } extern int slow_work_enqueue(struct slow_work *work); +extern void slow_work_cancel(struct slow_work *work); extern int slow_work_register_user(struct module *owner); extern void slow_work_unregister_user(struct module *owner); diff --git a/kernel/slow-work.c b/kernel/slow-work.c index fccf421..671cc43 100644 --- a/kernel/slow-work.c +++ b/kernel/slow-work.c @@ -236,12 +236,17 @@ static bool slow_work_execute(int id) if (!test_and_clear_bit(SLOW_WORK_PENDING, &work->flags)) BUG(); - work->ops->execute(work); + /* don't execute if the work is in the process of being cancelled */ + if (!test_bit(SLOW_WORK_CANCELLING, &work->flags)) + work->ops->execute(work); if (very_slow) atomic_dec(&vslow_work_executing_count); clear_bit_unlock(SLOW_WORK_EXECUTING, &work->flags); + /* wake up anyone waiting for this work to be complete */ + wake_up_bit(&work->flags, SLOW_WORK_EXECUTING); + /* if someone tried to enqueue the item whilst we were executing it, * then it'll be left unenqueued to avoid multiple threads trying to * execute it simultaneously @@ -314,11 +319,16 @@ auto_requeue: * allowed to pick items to execute. This ensures that very slow items won't * overly block ones that are just ordinarily slow. * - * Returns 0 if successful, -EAGAIN if not. + * Returns 0 if successful, -EAGAIN if not (or -ECANCELED if cancelled work is + * attempted queued) */ int slow_work_enqueue(struct slow_work *work) { unsigned long flags; + int ret; + + if (test_bit(SLOW_WORK_CANCELLING, &work->flags)) + return -ECANCELED; BUG_ON(slow_work_user_count <= 0); BUG_ON(!work); @@ -335,6 +345,9 @@ int slow_work_enqueue(struct slow_work *work) if (!test_and_set_bit_lock(SLOW_WORK_PENDING, &work->flags)) { spin_lock_irqsave(&slow_work_queue_lock, flags); + if (unlikely(test_bit(SLOW_WORK_CANCELLING, &work->flags))) + goto cancelled; + /* we promise that we will not attempt to execute the work * function in more than one thread simultaneously * @@ -352,8 +365,9 @@ int slow_work_enqueue(struct slow_work *work) if (test_bit(SLOW_WORK_EXECUTING, &work->flags)) { set_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags); } else { - if (slow_work_get_ref(work) < 0) - goto cant_get_ref; + ret = slow_work_get_ref(work); + if (ret < 0) + goto failed; if (test_bit(SLOW_WORK_VERY_SLOW, &work->flags)) list_add_tail(&work->link, &vslow_work_queue); else @@ -365,12 +379,67 @@ int slow_work_enqueue(struct slow_work *work) } return 0; -cant_get_ref: +cancelled: + ret = -ECANCELED; +failed: spin_unlock_irqrestore(&slow_work_queue_lock, flags); - return -EAGAIN; + return ret; } EXPORT_SYMBOL(slow_work_enqueue); +static int slow_work_wait(void *word) +{ + schedule(); + return 0; +} + +/** + * slow_work_cancel - Cancel a slow work item + * @work: The work item to cancel + * + * This function will cancel a previously enqueued work item. If we cannot + * cancel the work item, it is guarenteed to have run when this function + * returns. + */ +void slow_work_cancel(struct slow_work *work) +{ + bool wait = true, put = false; + + set_bit(SLOW_WORK_CANCELLING, &work->flags); + + spin_lock_irq(&slow_work_queue_lock); + + if (test_bit(SLOW_WORK_PENDING, &work->flags) && + !list_empty(&work->link)) { + /* the link in the pending queue holds a reference on the item + * that we will need to release */ + list_del_init(&work->link); + wait = false; + put = true; + clear_bit(SLOW_WORK_PENDING, &work->flags); + + } else if (test_and_clear_bit(SLOW_WORK_ENQ_DEFERRED, &work->flags)) { + /* the executor is holding our only reference on the item, so + * we merely need to wait for it to finish executing */ + clear_bit(SLOW_WORK_PENDING, &work->flags); + } + + spin_unlock_irq(&slow_work_queue_lock); + + /* the EXECUTING flag is set by the executor whilst the spinlock is set + * and before the item is dequeued - so assuming the above doesn't + * actually dequeue it, simply waiting for the EXECUTING flag to be + * released here should be sufficient */ + if (wait) + wait_on_bit(&work->flags, SLOW_WORK_EXECUTING, slow_work_wait, + TASK_UNINTERRUPTIBLE); + + clear_bit(SLOW_WORK_CANCELLING, &work->flags); + if (put) + slow_work_put_ref(work); +} +EXPORT_SYMBOL(slow_work_cancel); + /* * Schedule a cull of the thread pool at some time in the near future */ |