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43aa6f97c2
The eventfs inode had pointers to dentries (and child dentries) without
actually holding a refcount on said pointer. That is fundamentally
broken, and while eventfs tried to then maintain coherence with dentries
going away by hooking into the '.d_iput' callback, that doesn't actually
work since it's not ordered wrt lookups.
There were two reasonms why eventfs tried to keep a pointer to a dentry:
- the creation of a 'events' directory would actually have a stable
dentry pointer that it created with tracefs_start_creating().
And it needed that dentry when tearing it all down again in
eventfs_remove_events_dir().
This use is actually ok, because the special top-level events
directory dentries are actually stable, not just a temporary cache of
the eventfs data structures.
- the 'eventfs_inode' (aka ei) needs to stay around as long as there
are dentries that refer to it.
It then used these dentry pointers as a replacement for doing
reference counting: it would try to make sure that there was only
ever one dentry associated with an event_inode, and keep a child
dentry array around to see which dentries might still refer to the
parent ei.
This gets rid of the invalid dentry pointer use, and renames the one
valid case to a different name to make it clear that it's not just any
random dentry.
The magic child dentry array that is kind of a "reverse reference list"
is simply replaced by having child dentries take a ref to the ei. As
does the directory dentries. That makes the broken use case go away.
Link: https://lore.kernel.org/linux-trace-kernel/202401291043.e62e89dc-oliver.sang@intel.com/
Link: https://lore.kernel.org/linux-trace-kernel/20240131185513.280463000@goodmis.org
Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Ajay Kaher <ajay.kaher@broadcom.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Fixes: c1504e5102 ("eventfs: Implement eventfs dir creation functions")
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
83 lines
2.4 KiB
C
83 lines
2.4 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _TRACEFS_INTERNAL_H
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#define _TRACEFS_INTERNAL_H
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enum {
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TRACEFS_EVENT_INODE = BIT(1),
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TRACEFS_EVENT_TOP_INODE = BIT(2),
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TRACEFS_GID_PERM_SET = BIT(3),
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TRACEFS_UID_PERM_SET = BIT(4),
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TRACEFS_INSTANCE_INODE = BIT(5),
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};
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struct tracefs_inode {
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struct inode vfs_inode;
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/* The below gets initialized with memset_after(ti, 0, vfs_inode) */
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unsigned long flags;
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void *private;
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};
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/*
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* struct eventfs_attr - cache the mode and ownership of a eventfs entry
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* @mode: saved mode plus flags of what is saved
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* @uid: saved uid if changed
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* @gid: saved gid if changed
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*/
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struct eventfs_attr {
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int mode;
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kuid_t uid;
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kgid_t gid;
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};
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/*
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* struct eventfs_inode - hold the properties of the eventfs directories.
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* @list: link list into the parent directory
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* @entries: the array of entries representing the files in the directory
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* @name: the name of the directory to create
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* @children: link list into the child eventfs_inode
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* @events_dir: the dentry of the events directory
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* @entry_attrs: Saved mode and ownership of the @d_children
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* @attr: Saved mode and ownership of eventfs_inode itself
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* @data: The private data to pass to the callbacks
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* @is_freed: Flag set if the eventfs is on its way to be freed
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* Note if is_freed is set, then dentry is corrupted.
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* @nr_entries: The number of items in @entries
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*/
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struct eventfs_inode {
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struct kref kref;
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struct list_head list;
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const struct eventfs_entry *entries;
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const char *name;
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struct list_head children;
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struct dentry *events_dir;
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struct eventfs_attr *entry_attrs;
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struct eventfs_attr attr;
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void *data;
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unsigned int is_freed:1;
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unsigned int is_events:1;
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unsigned int nr_entries:30;
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unsigned int ino;
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/*
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* Union - used for deletion
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* @llist: for calling dput() if needed after RCU
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* @rcu: eventfs_inode to delete in RCU
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*/
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union {
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struct llist_node llist;
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struct rcu_head rcu;
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};
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};
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static inline struct tracefs_inode *get_tracefs(const struct inode *inode)
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{
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return container_of(inode, struct tracefs_inode, vfs_inode);
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}
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struct dentry *tracefs_start_creating(const char *name, struct dentry *parent);
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struct dentry *tracefs_end_creating(struct dentry *dentry);
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struct dentry *tracefs_failed_creating(struct dentry *dentry);
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struct inode *tracefs_get_inode(struct super_block *sb);
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void eventfs_d_release(struct dentry *dentry);
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#endif /* _TRACEFS_INTERNAL_H */
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