linux-kernel - [PATCH v4 2/4] fsnotify: Simplify inode iteration on umount

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Date:	Thu, 25 Feb 2016 19:08:42 -0500
From:	Waiman Long <Waiman.Long@....com>
To:	Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.com>,
	Jeff Layton <jlayton@...chiereds.net>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Tejun Heo <tj@...nel.org>,
	Christoph Lameter <cl@...ux-foundation.org>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andi Kleen <andi@...stfloor.org>,
	Dave Chinner <dchinner@...hat.com>,
	Scott J Norton <scott.norton@...com>,
	Douglas Hatch <doug.hatch@...com>, Jan Kara <jack@...e.cz>,
	Waiman Long <Waiman.Long@....com>
Subject: [PATCH v4 2/4] fsnotify: Simplify inode iteration on umount

From: Jan Kara <jack@...e.cz>

fsnotify_unmount_inodes() played complex tricks to pin next inode in the
sb->s_inodes list when iterating over all inodes. If we switch to
keeping current inode pinned somewhat longer, we can make the code much
simpler and standard.

Signed-off-by: Jan Kara <jack@...e.cz>
Signed-off-by: Waiman Long <Waiman.Long@....com>
---
 fs/notify/inode_mark.c |   45 +++++++++------------------------------------
 1 files changed, 9 insertions(+), 36 deletions(-)

diff --git a/fs/notify/inode_mark.c b/fs/notify/inode_mark.c
index 741077d..a364524 100644
--- a/fs/notify/inode_mark.c
+++ b/fs/notify/inode_mark.c
@@ -150,12 +150,10 @@ int fsnotify_add_inode_mark(struct fsnotify_mark *mark,
  */
 void fsnotify_unmount_inodes(struct super_block *sb)
 {
-	struct inode *inode, *next_i, *need_iput = NULL;
+	struct inode *inode, *iput_inode = NULL;
 
 	spin_lock(&sb->s_inode_list_lock);
-	list_for_each_entry_safe(inode, next_i, &sb->s_inodes, i_sb_list) {
-		struct inode *need_iput_tmp;
-
+	list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
 		/*
 		 * We cannot __iget() an inode in state I_FREEING,
 		 * I_WILL_FREE, or I_NEW which is fine because by that point
@@ -178,49 +176,24 @@ void fsnotify_unmount_inodes(struct super_block *sb)
 			continue;
 		}
 
-		need_iput_tmp = need_iput;
-		need_iput = NULL;
-
-		/* In case fsnotify_inode_delete() drops a reference. */
-		if (inode != need_iput_tmp)
-			__iget(inode);
-		else
-			need_iput_tmp = NULL;
+		__iget(inode);
 		spin_unlock(&inode->i_lock);
-
-		/* In case the dropping of a reference would nuke next_i. */
-		while (&next_i->i_sb_list != &sb->s_inodes) {
-			spin_lock(&next_i->i_lock);
-			if (!(next_i->i_state & (I_FREEING | I_WILL_FREE)) &&
-						atomic_read(&next_i->i_count)) {
-				__iget(next_i);
-				need_iput = next_i;
-				spin_unlock(&next_i->i_lock);
-				break;
-			}
-			spin_unlock(&next_i->i_lock);
-			next_i = list_next_entry(next_i, i_sb_list);
-		}
-
-		/*
-		 * We can safely drop s_inode_list_lock here because either
-		 * we actually hold references on both inode and next_i or
-		 * end of list.  Also no new inodes will be added since the
-		 * umount has begun.
-		 */
 		spin_unlock(&sb->s_inode_list_lock);
 
-		if (need_iput_tmp)
-			iput(need_iput_tmp);
+		if (iput_inode)
+			iput(iput_inode);
 
 		/* for each watch, send FS_UNMOUNT and then remove it */
 		fsnotify(inode, FS_UNMOUNT, inode, FSNOTIFY_EVENT_INODE, NULL, 0);
 
 		fsnotify_inode_delete(inode);
 
-		iput(inode);
+		iput_inode = inode;
 
 		spin_lock(&sb->s_inode_list_lock);
 	}
 	spin_unlock(&sb->s_inode_list_lock);
+
+	if (iput_inode)
+		iput(iput_inode);
 }
-- 
1.7.1