Re: [PATCH 3/6] tracefs: dentry lookup crapectomy

Al Viro
2024-01-30T23:26:26Z

On Tue, Jan 30, 2024 at 11:03:52AM -0800, Linus Torvalds wrote:
> The dentry lookup for eventfs files was very broken, and had lots of
> signs of the old situation where the filesystem names were all created
> statically in the dentry tree, rather than being looked up dynamically
> based on the eventfs data structures.
>
> You could see it in the naming - how it claimed to "create" dentries
> rather than just look up the dentries that were given it.
>
> You could see it in various nonsensical and very incorrect operations,
> like using "simple_lookup()" on the dentries that were passed in, which
> only results in those dentries becoming negative dentries. Which meant
> that any other lookup would possibly return ENOENT if it saw that
> negative dentry before the data rwas then later filled in.
>
> You could see it in the immesnse amount of nonsensical code that didn't
> actually just do lookups.

> -static struct dentry *create_file(const char *name, umode_t mode,
> +static struct dentry *lookup_file(struct dentry *dentry,
> + umode_t mode,
> struct eventfs_attr *attr,
> - struct dentry *parent, void *data,
> + void *data,
> const struct file_operations *fop)
> {
> struct tracefs_inode *ti;
> - struct dentry *dentry;
> struct inode *inode;
>
> if (!(mode & S_IFMT))
> @@ -307,12 +304,6 @@ static struct dentry *create_file(const char *name, umode_t mode,
> if (WARN_ON_ONCE(!S_ISREG(mode)))
> return NULL;
>
> - WARN_ON_ONCE(!parent);
> - dentry = eventfs_start_creating(name, parent);

Used to lock the inode of parent.

> if (unlikely(!inode))
> return eventfs_failed_creating(dentry);

... and that still unlocks it.

> @@ -331,29 +322,25 @@ static struct dentry *create_file(const char *name, umode_t mode,
> ti->flags = TRACEFS_EVENT_INODE;
> ti->private = NULL; // Directories have 'ei', files not
>
> - d_instantiate(dentry, inode);
> + d_add(dentry, inode);
> fsnotify_create(dentry->d_parent->d_inode, dentry);
> return eventfs_end_creating(dentry);

... and so does this.

> };

Where has that inode_lock() gone and how could that possibly work?