[patch 049/192] writeback, cgroup: switch to rcu_work API in inode_switch_wbs()

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From: Roman Gushchin <guro@xxxxxx>
Subject: writeback, cgroup: switch to rcu_work API in inode_switch_wbs()

Inode's wb switching requires two steps divided by an RCU grace period. 
It's currently implemented as an RCU callback inode_switch_wbs_rcu_fn(),
which schedules inode_switch_wbs_work_fn() as a work.

Switching to the rcu_work API allows to do the same in a cleaner and
slightly shorter form.

Link: https://lkml.kernel.org/r/20210608230225.2078447-5-guro@xxxxxx
Signed-off-by: Roman Gushchin <guro@xxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Acked-by: Tejun Heo <tj@xxxxxxxxxx>
Acked-by: Dennis Zhou <dennis@xxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Dave Chinner <dchinner@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 fs/fs-writeback.c |   18 ++++--------------
 1 file changed, 4 insertions(+), 14 deletions(-)

--- a/fs/fs-writeback.c~writeback-cgroup-switch-to-rcu_work-api-in-inode_switch_wbs
+++ a/fs/fs-writeback.c
@@ -335,8 +335,7 @@ struct inode_switch_wbs_context {
 	struct inode		*inode;
 	struct bdi_writeback	*new_wb;
 
-	struct rcu_head		rcu_head;
-	struct work_struct	work;
+	struct rcu_work		work;
 };
 
 static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi)
@@ -352,7 +351,7 @@ static void bdi_up_write_wb_switch_rwsem
 static void inode_switch_wbs_work_fn(struct work_struct *work)
 {
 	struct inode_switch_wbs_context *isw =
-		container_of(work, struct inode_switch_wbs_context, work);
+		container_of(to_rcu_work(work), struct inode_switch_wbs_context, work);
 	struct inode *inode = isw->inode;
 	struct backing_dev_info *bdi = inode_to_bdi(inode);
 	struct address_space *mapping = inode->i_mapping;
@@ -469,16 +468,6 @@ skip_switch:
 	atomic_dec(&isw_nr_in_flight);
 }
 
-static void inode_switch_wbs_rcu_fn(struct rcu_head *rcu_head)
-{
-	struct inode_switch_wbs_context *isw = container_of(rcu_head,
-				struct inode_switch_wbs_context, rcu_head);
-
-	/* needs to grab bh-unsafe locks, bounce to work item */
-	INIT_WORK(&isw->work, inode_switch_wbs_work_fn);
-	queue_work(isw_wq, &isw->work);
-}
-
 /**
  * inode_switch_wbs - change the wb association of an inode
  * @inode: target inode
@@ -536,7 +525,8 @@ static void inode_switch_wbs(struct inod
 	 * lock so that stat transfer can synchronize against them.
 	 * Let's continue after I_WB_SWITCH is guaranteed to be visible.
 	 */
-	call_rcu(&isw->rcu_head, inode_switch_wbs_rcu_fn);
+	INIT_RCU_WORK(&isw->work, inode_switch_wbs_work_fn);
+	queue_rcu_work(isw_wq, &isw->work);
 	return;
 
 out_free:
_



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