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From:   Stephen Brennan <stephen.s.brennan@oracle.com>
To:     Jan Kara <jack@suse.cz>
Cc:     linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        Amir Goldstein <amir73il@gmail.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Stephen Brennan <stephen.s.brennan@oracle.com>
Subject: [PATCH v3 1/3] fsnotify: Use d_find_any_alias to get dentry associated with inode
Date:   Thu, 27 Oct 2022 17:10:14 -0700
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Rather than iterating over the inode's i_dentry (requiring holding the
i_lock for the entire duration of the function), we know that there
should be only one item in the list. Use d_find_any_alias() and no
longer hold i_lock.

Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
---

Notes:
    Changes since v2:
    - Add newlines in block comment
    - d_find_any_alias() returns a reference, which I was leaking. Add
      a dput(alias) at the end.
    - Add Amir's R-b

 fs/notify/fsnotify.c | 44 +++++++++++++++++++++-----------------------
 1 file changed, 21 insertions(+), 23 deletions(-)

diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index 7974e91ffe13..7939aa911931 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -105,7 +105,7 @@ void fsnotify_sb_delete(struct super_block *sb)
  */
 void __fsnotify_update_child_dentry_flags(struct inode *inode)
 {
-	struct dentry *alias;
+	struct dentry *alias, *child;
 	int watched;
 
 	if (!S_ISDIR(inode->i_mode))
@@ -114,30 +114,28 @@ void __fsnotify_update_child_dentry_flags(struct inode *inode)
 	/* determine if the children should tell inode about their events */
 	watched = fsnotify_inode_watches_children(inode);
 
-	spin_lock(&inode->i_lock);
-	/* run all of the dentries associated with this inode.  Since this is a
-	 * directory, there damn well better only be one item on this list */
-	hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
-		struct dentry *child;
-
-		/* run all of the children of the original inode and fix their
-		 * d_flags to indicate parental interest (their parent is the
-		 * original inode) */
-		spin_lock(&alias->d_lock);
-		list_for_each_entry(child, &alias->d_subdirs, d_child) {
-			if (!child->d_inode)
-				continue;
+	/* Since this is a directory, there damn well better only be one child */
+	alias = d_find_any_alias(inode);
 
-			spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);
-			if (watched)
-				child->d_flags |= DCACHE_FSNOTIFY_PARENT_WATCHED;
-			else
-				child->d_flags &= ~DCACHE_FSNOTIFY_PARENT_WATCHED;
-			spin_unlock(&child->d_lock);
-		}
-		spin_unlock(&alias->d_lock);
+	/*
+	 * run all of the children of the original inode and fix their
+	 * d_flags to indicate parental interest (their parent is the
+	 * original inode)
+	 */
+	spin_lock(&alias->d_lock);
+	list_for_each_entry(child, &alias->d_subdirs, d_child) {
+		if (!child->d_inode)
+			continue;
+
+		spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);
+		if (watched)
+			child->d_flags |= DCACHE_FSNOTIFY_PARENT_WATCHED;
+		else
+			child->d_flags &= ~DCACHE_FSNOTIFY_PARENT_WATCHED;
+		spin_unlock(&child->d_lock);
 	}
-	spin_unlock(&inode->i_lock);
+	spin_unlock(&alias->d_lock);
+	dput(alias);
 }
 
 /* Are inode/sb/mount interested in parent and name info with this event? */
-- 
2.34.1