linux-kernel - [PATCH] workqueue: detach rescuer from pool until the last

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Date:	Wed, 16 Jul 2014 14:56:50 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	<linux-kernel@...r.kernel.org>
CC:	Tejun Heo <tj@...nel.org>, Lai Jiangshan <laijs@...fujitsu.com>
Subject: [PATCH] workqueue: detach rescuer from pool until the last

In 51697d393922 ("workqueue: use generic attach/detach routine for rescuers"),
The rescuer detaches itself from the pool before put_pwq() so that
the put_unbound_pool() will not destroy the rescuer-attached pool.

It is unnecessary, worker_detach_from_pool() can be used as the last
statement to access to the pool as the same as the regular workers,
put_unbound_pool() will wait for it to detach and then free the pool.

So we move the worker_detach_from_pool() down, make it coincide with
the regular workers.

Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
---
This old logic is introduced by the same-purpose but un-accepted patch:
https://lkml.org/lkml/2014/4/12/26

In the old patch, put_unbound_pool() still synchronizes with the workers
exiting via kthread_stop() which means put_unbound_pool() can't destroy the
rescuer-attached pool, so the put_pwq() should be the last statement
for the rescuer.

And after several versions of the patchset, the put_unbound_pool() was
re-implemented and it can wait any un-detached worker including the
rescuers, but the above mentioned old logic is still kept in the code.

The old logic is still correct now, but not grace nor necessary.

 kernel/workqueue.c |    12 +++++-------
 1 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index a791a8c..dfd9f68 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2300,11 +2300,6 @@ repeat:
 				move_linked_works(work, scheduled, &n);

 		process_scheduled_works(rescuer);
-		spin_unlock_irq(&pool->lock);
-
-		worker_detach_from_pool(rescuer, pool);
-
-		spin_lock_irq(&pool->lock);

 		/*
 		 * Put the reference grabbed by send_mayday().  @pool won't
@@ -2322,8 +2317,11 @@ repeat:
 			wake_up_worker(pool);

 		rescuer->pool = NULL;
-		spin_unlock(&pool->lock);
-		spin_lock(&wq_mayday_lock);
+		spin_unlock_irq(&pool->lock);
+
+		worker_detach_from_pool(rescuer, pool);
+
+		spin_lock_irq(&wq_mayday_lock);
 	}

 	spin_unlock_irq(&wq_mayday_lock);
-- 
1.7.4.4

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