linux-kernel - [PATCH wq/for-3.9] workqueue: make work->data point to pool after try_to_grab

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Message-ID: <20130207005302.GH2875@htj.dyndns.org>
Date:	Wed, 6 Feb 2013 16:53:02 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH wq/for-3.9] workqueue: make work->data point to pool after
 try_to_grab_pending()

From: Lai Jiangshan <laijs@...fujitsu.com>

We plan to use work->data pointing to cwq as the synchronization
invariant when determining whether a given work item is on a locked
pool or not, which requires work->data pointing to cwq only while the
work item is queued on the associated pool.

With delayed_work updated not to overload work->data for target
workqueue recording, the only case where we still have off-queue
work->data pointing to cwq is try_to_grab_pending() which doesn't
update work->data after stealing a queued work item.  There's no
reason for try_to_grab_pending() to not update work->data to point to
the pool instead of cwq, like the normal execution does.

This patch adds set_work_pool_and_keep_pending() which makes
work->data point to pool instead of cwq but keeps the pending bit
unlike set_work_pool_and_clear_pending() (surprise!).

After this patch, it's guaranteed that only queued work items point to
cwqs.

This patch doesn't introduce any visible behavior change.

tj: Renamed the new helper function to match
    set_work_pool_and_clear_pending() and rewrote the description.

Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
Signed-off-by: Tejun Heo <tj@...nel.org>
---
 kernel/workqueue.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -556,6 +556,13 @@ static void set_work_cwq(struct work_str
 		      WORK_STRUCT_PENDING | WORK_STRUCT_CWQ | extra_flags);
 }

+static void set_work_pool_and_keep_pending(struct work_struct *work,
+					   int pool_id)
+{
+	set_work_data(work, (unsigned long)pool_id << WORK_OFFQ_POOL_SHIFT,
+		      WORK_STRUCT_PENDING);
+}
+
 static void set_work_pool_and_clear_pending(struct work_struct *work,
 					    int pool_id)
 {
@@ -1115,6 +1122,9 @@ static int try_to_grab_pending(struct wo
 			cwq_dec_nr_in_flight(get_work_cwq(work),
 				get_work_color(work));

+			/* work->data points to cwq iff queued, point to pool */
+			set_work_pool_and_keep_pending(work, pool->id);
+
 			spin_unlock(&pool->lock);
 			return 1;
 		}
--
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