Re: [PATCH v4 2/5] fsnotify: Use d_find_any_alias to get dentry associated with inode

Amir Goldstein
2022-11-12T08:53:45Z

On Sat, Nov 12, 2022 at 12:06 AM Stephen Brennan
<stephen.s.brennan@oracle.com> wrote:
>
> 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 in v4:
> - Bail out if d_find_any_alias() returns NULL
> - Rebase on Amir's patch
> Changes in v3:
> - 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 | 46 ++++++++++++++++++++++----------------------
> 1 file changed, 23 insertions(+), 23 deletions(-)
>
> diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
> index 2c50e9e50d35..409d479cbbc6 100644
> --- a/fs/notify/fsnotify.c
> +++ b/fs/notify/fsnotify.c
> @@ -105,35 +105,35 @@ void fsnotify_sb_delete(struct super_block *sb)
> */
> void fsnotify_update_children_dentry_flags(struct inode *inode, bool watched)
> {
> - struct dentry *alias;
> + struct dentry *alias, *child;
>
> if (!S_ISDIR(inode->i_mode))
> return;
>
> - 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);
> + if (!alias)
> + return;
>
> - 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)

nit: this comment can probably fit in two nicer lines

> + */
> + 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);
> }
>
> /*
> --
> 2.34.1
>