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authorTejun Heo <tj@kernel.org>2010-08-25 10:33:56 +0200
committerTejun Heo <tj@kernel.org>2010-08-25 10:33:56 +0200
commit8a2e8e5dec7e29c56a46ba176c664ab6a3d04118 (patch)
tree57da96451bead4986dfcd82aadf47ba2c05745ac /kernel
parente41e704bc4f49057fc68b643108366e6e6781aa3 (diff)
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workqueue: fix cwq->nr_active underflow
cwq->nr_active is used to keep track of how many work items are active for the cpu workqueue, where 'active' is defined as either pending on global worklist or executing. This is used to implement the max_active limit and workqueue freezing. If a work item is queued after nr_active has already reached max_active, the work item doesn't increment nr_active and is put on the delayed queue and gets activated later as previous active work items retire. try_to_grab_pending() which is used in the cancellation path unconditionally decremented nr_active whether the work item being cancelled is currently active or delayed, so cancelling a delayed work item makes nr_active underflow. This breaks max_active enforcement and triggers BUG_ON() in destroy_workqueue() later on. This patch fixes this bug by adding a flag WORK_STRUCT_DELAYED, which is set while a work item in on the delayed list and making try_to_grab_pending() decrement nr_active iff the work item is currently active. The addition of the flag enlarges cwq alignment to 256 bytes which is getting a bit too large. It's scheduled to be reduced back to 128 bytes by merging WORK_STRUCT_PENDING and WORK_STRUCT_CWQ in the next devel cycle. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Johannes Berg <johannes@sipsolutions.net>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/workqueue.c30
1 files changed, 20 insertions, 10 deletions
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 362b50d092e..a2dccfca03b 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -941,6 +941,7 @@ static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,
struct global_cwq *gcwq;
struct cpu_workqueue_struct *cwq;
struct list_head *worklist;
+ unsigned int work_flags;
unsigned long flags;
debug_work_activate(work);
@@ -990,14 +991,17 @@ static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,
BUG_ON(!list_empty(&work->entry));
cwq->nr_in_flight[cwq->work_color]++;
+ work_flags = work_color_to_flags(cwq->work_color);
if (likely(cwq->nr_active < cwq->max_active)) {
cwq->nr_active++;
worklist = gcwq_determine_ins_pos(gcwq, cwq);
- } else
+ } else {
+ work_flags |= WORK_STRUCT_DELAYED;
worklist = &cwq->delayed_works;
+ }
- insert_work(cwq, work, worklist, work_color_to_flags(cwq->work_color));
+ insert_work(cwq, work, worklist, work_flags);
spin_unlock_irqrestore(&gcwq->lock, flags);
}
@@ -1666,6 +1670,7 @@ static void cwq_activate_first_delayed(struct cpu_workqueue_struct *cwq)
struct list_head *pos = gcwq_determine_ins_pos(cwq->gcwq, cwq);
move_linked_works(work, pos, NULL);
+ __clear_bit(WORK_STRUCT_DELAYED_BIT, work_data_bits(work));
cwq->nr_active++;
}
@@ -1673,6 +1678,7 @@ static void cwq_activate_first_delayed(struct cpu_workqueue_struct *cwq)
* cwq_dec_nr_in_flight - decrement cwq's nr_in_flight
* @cwq: cwq of interest
* @color: color of work which left the queue
+ * @delayed: for a delayed work
*
* A work either has completed or is removed from pending queue,
* decrement nr_in_flight of its cwq and handle workqueue flushing.
@@ -1680,19 +1686,22 @@ static void cwq_activate_first_delayed(struct cpu_workqueue_struct *cwq)
* CONTEXT:
* spin_lock_irq(gcwq->lock).
*/
-static void cwq_dec_nr_in_flight(struct cpu_workqueue_struct *cwq, int color)
+static void cwq_dec_nr_in_flight(struct cpu_workqueue_struct *cwq, int color,
+ bool delayed)
{
/* ignore uncolored works */
if (color == WORK_NO_COLOR)
return;
cwq->nr_in_flight[color]--;
- cwq->nr_active--;
- if (!list_empty(&cwq->delayed_works)) {
- /* one down, submit a delayed one */
- if (cwq->nr_active < cwq->max_active)
- cwq_activate_first_delayed(cwq);
+ if (!delayed) {
+ cwq->nr_active--;
+ if (!list_empty(&cwq->delayed_works)) {
+ /* one down, submit a delayed one */
+ if (cwq->nr_active < cwq->max_active)
+ cwq_activate_first_delayed(cwq);
+ }
}
/* is flush in progress and are we at the flushing tip? */
@@ -1823,7 +1832,7 @@ __acquires(&gcwq->lock)
hlist_del_init(&worker->hentry);
worker->current_work = NULL;
worker->current_cwq = NULL;
- cwq_dec_nr_in_flight(cwq, work_color);
+ cwq_dec_nr_in_flight(cwq, work_color, false);
}
/**
@@ -2388,7 +2397,8 @@ static int try_to_grab_pending(struct work_struct *work)
debug_work_deactivate(work);
list_del_init(&work->entry);
cwq_dec_nr_in_flight(get_work_cwq(work),
- get_work_color(work));
+ get_work_color(work),
+ *work_data_bits(work) & WORK_STRUCT_DELAYED);
ret = 1;
}
}