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author | Oleg Nesterov <oleg@tv-sign.ru> | 2007-05-23 13:57:57 -0700 |
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committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2007-05-23 20:14:13 -0700 |
commit | 14441960e8c27a64487e0b455b323e784f33583f (patch) | |
tree | bc224f965db3951edbbee7e776e334187b5a32d6 /kernel | |
parent | 3fcbc72965f767bb5c4518aef754c28f45fc6147 (diff) | |
download | linux-14441960e8c27a64487e0b455b323e784f33583f.tar.gz linux-14441960e8c27a64487e0b455b323e784f33583f.tar.bz2 linux-14441960e8c27a64487e0b455b323e784f33583f.zip |
simplify cleanup_workqueue_thread()
cleanup_workqueue_thread() and cwq_should_stop() are overcomplicated.
Convert the code to use kthread_should_stop/kthread_stop as was
suggested by Gautham and Srivatsa.
In particular this patch removes the (unlikely) busy-wait loop from the
exit path, it was a temporary and ugly kludge (if not a bug).
Note: the current code was designed to solve another old problem:
work->func can't share locks with hotplug callbacks. I think this could
be done, see
http://marc.info/?l=linux-kernel&m=116905366428633
but this needs some more complications to preserve CPU affinity of
cwq->thread during cpu_up(). A freezer-based hotplug looks more
appealing.
[akpm@linux-foundation.org: make it more tolerant of gcc borkenness]
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Zilvinas Valinskas <zilvinas@wilibox.com>
Cc: Gautham R Shenoy <ego@in.ibm.com>
Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/workqueue.c | 84 |
1 files changed, 37 insertions, 47 deletions
diff --git a/kernel/workqueue.c b/kernel/workqueue.c index fb56fedd5c02..3bebf73be976 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -47,7 +47,6 @@ struct cpu_workqueue_struct { struct workqueue_struct *wq; struct task_struct *thread; - int should_stop; int run_depth; /* Detect run_workqueue() recursion depth */ } ____cacheline_aligned; @@ -71,7 +70,13 @@ static LIST_HEAD(workqueues); static int singlethread_cpu __read_mostly; static cpumask_t cpu_singlethread_map __read_mostly; -/* optimization, we could use cpu_possible_map */ +/* + * _cpu_down() first removes CPU from cpu_online_map, then CPU_DEAD + * flushes cwq->worklist. This means that flush_workqueue/wait_on_work + * which comes in between can't use for_each_online_cpu(). We could + * use cpu_possible_map, the cpumask below is more a documentation + * than optimization. + */ static cpumask_t cpu_populated_map __read_mostly; /* If it's single threaded, it isn't in the list of workqueues. */ @@ -272,24 +277,6 @@ static void run_workqueue(struct cpu_workqueue_struct *cwq) spin_unlock_irq(&cwq->lock); } -/* - * NOTE: the caller must not touch *cwq if this func returns true - */ -static int cwq_should_stop(struct cpu_workqueue_struct *cwq) -{ - int should_stop = cwq->should_stop; - - if (unlikely(should_stop)) { - spin_lock_irq(&cwq->lock); - should_stop = cwq->should_stop && list_empty(&cwq->worklist); - if (should_stop) - cwq->thread = NULL; - spin_unlock_irq(&cwq->lock); - } - - return should_stop; -} - static int worker_thread(void *__cwq) { struct cpu_workqueue_struct *cwq = __cwq; @@ -302,14 +289,15 @@ static int worker_thread(void *__cwq) for (;;) { prepare_to_wait(&cwq->more_work, &wait, TASK_INTERRUPTIBLE); - if (!freezing(current) && !cwq->should_stop - && list_empty(&cwq->worklist)) + if (!freezing(current) && + !kthread_should_stop() && + list_empty(&cwq->worklist)) schedule(); finish_wait(&cwq->more_work, &wait); try_to_freeze(); - if (cwq_should_stop(cwq)) + if (kthread_should_stop()) break; run_workqueue(cwq); @@ -340,18 +328,21 @@ static void insert_wq_barrier(struct cpu_workqueue_struct *cwq, insert_work(cwq, &barr->work, tail); } -static void flush_cpu_workqueue(struct cpu_workqueue_struct *cwq) +static int flush_cpu_workqueue(struct cpu_workqueue_struct *cwq) { + int active; + if (cwq->thread == current) { /* * Probably keventd trying to flush its own queue. So simply run * it by hand rather than deadlocking. */ run_workqueue(cwq); + active = 1; } else { struct wq_barrier barr; - int active = 0; + active = 0; spin_lock_irq(&cwq->lock); if (!list_empty(&cwq->worklist) || cwq->current_work != NULL) { insert_wq_barrier(cwq, &barr, 1); @@ -362,6 +353,8 @@ static void flush_cpu_workqueue(struct cpu_workqueue_struct *cwq) if (active) wait_for_completion(&barr.done); } + + return active; } /** @@ -674,7 +667,6 @@ static int create_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu) return PTR_ERR(p); cwq->thread = p; - cwq->should_stop = 0; return 0; } @@ -740,29 +732,27 @@ EXPORT_SYMBOL_GPL(__create_workqueue); static void cleanup_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu) { - struct wq_barrier barr; - int alive = 0; - - spin_lock_irq(&cwq->lock); - if (cwq->thread != NULL) { - insert_wq_barrier(cwq, &barr, 1); - cwq->should_stop = 1; - alive = 1; - } - spin_unlock_irq(&cwq->lock); + /* + * Our caller is either destroy_workqueue() or CPU_DEAD, + * workqueue_mutex protects cwq->thread + */ + if (cwq->thread == NULL) + return; - if (alive) { - wait_for_completion(&barr.done); + /* + * If the caller is CPU_DEAD the single flush_cpu_workqueue() + * is not enough, a concurrent flush_workqueue() can insert a + * barrier after us. + * When ->worklist becomes empty it is safe to exit because no + * more work_structs can be queued on this cwq: flush_workqueue + * checks list_empty(), and a "normal" queue_work() can't use + * a dead CPU. + */ + while (flush_cpu_workqueue(cwq)) + ; - while (unlikely(cwq->thread != NULL)) - cpu_relax(); - /* - * Wait until cwq->thread unlocks cwq->lock, - * it won't touch *cwq after that. - */ - smp_rmb(); - spin_unlock_wait(&cwq->lock); - } + kthread_stop(cwq->thread); + cwq->thread = NULL; } /** |