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From:   Roman Gushchin <guro@fb.com>
To:     Jan Kara <jack@suse.cz>, Tejun Heo <tj@kernel.org>
CC:     <linux-fsdevel@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <linux-mm@kvack.org>, Alexander Viro <viro@zeniv.linux.org.uk>,
        Dennis Zhou <dennis@kernel.org>,
        Dave Chinner <dchinner@redhat.com>, <cgroups@vger.kernel.org>,
        Roman Gushchin <guro@fb.com>
Subject: [PATCH v7 2/6] writeback, cgroup: switch to rcu_work API in inode_switch_wbs()
Date:   Thu, 3 Jun 2021 18:31:55 -0700
Message-ID: <20210604013159.3126180-3-guro@fb.com>
In-Reply-To: <20210604013159.3126180-1-guro@fb.com>
References: <20210604013159.3126180-1-guro@fb.com>
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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.

Signed-off-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Jan Kara <jack@suse.cz>
---
 fs/fs-writeback.c | 18 ++++--------------
 1 file changed, 4 insertions(+), 14 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index bd99890599e0..9f378a670db4 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -335,8 +335,7 @@ struct inode_switch_wbs_context {
 	struct inode		*inode;
 	struct bdi_writeback	*new_wb;
=20
-	struct rcu_head		rcu_head;
-	struct work_struct	work;
+	struct rcu_work		work;
 };
=20
 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(struct backi=
ng_dev_info *bdi)
 static void inode_switch_wbs_work_fn(struct work_struct *work)
 {
 	struct inode_switch_wbs_context *isw =3D
-		container_of(work, struct inode_switch_wbs_context, work);
+		container_of(to_rcu_work(work), struct inode_switch_wbs_context, work)=
;
 	struct inode *inode =3D isw->inode;
 	struct backing_dev_info *bdi =3D inode_to_bdi(inode);
 	struct address_space *mapping =3D inode->i_mapping;
@@ -469,16 +468,6 @@ static void inode_switch_wbs_work_fn(struct work_str=
uct *work)
 	atomic_dec(&isw_nr_in_flight);
 }
=20
-static void inode_switch_wbs_rcu_fn(struct rcu_head *rcu_head)
-{
-	struct inode_switch_wbs_context *isw =3D 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
@@ -534,7 +523,8 @@ static void inode_switch_wbs(struct inode *inode, int=
 new_wb_id)
 	 * 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);
=20
 	atomic_inc(&isw_nr_in_flight);
 	return;
--=20
2.31.1