From: "Steven Rostedt (Google)" rostedt@goodmis.org

Looking at how dentry is removed via the tracefs system, I found that eventfs does not do everything that it did under tracefs. The tracefs removal of a dentry calls simple_recursive_removal() that does a lot more than a simple d_invalidate().

As it should be a requirement that any eventfs_inode that has a dentry, so does its parent. When removing a eventfs_inode, if it has a dentry, a call to simple_recursive_removal() on that dentry should clean up all the dentries underneath it.

Add WARN_ON_ONCE() to check for the parent having a dentry if any children do.

Link: https://lore.kernel.org/all/20231101022553.GE1957730@ZenIV/

Cc: stable@vger.kernel.org Cc: Al Viro viro@zeniv.linux.org.uk Fixes: 5bdcd5f5331a2 ("eventfs: Implement removal of meta data from eventfs") Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org --- Changes since the last patch: https://lore.kernel.org/linux-trace-kernel/20231031144703.71eef3a0@gandalf.l...

- Was originally called: eventfs: Process deletion of dentry more thoroughly

- Al Viro pointed out that I could use simple_recursive_removal() instead. I had originally thought that I could not, but looking deeper into it, and realizing that if a dentry exists on any eventfs_inode, then all the parent eventfs_inode of that would als have a dentry. Hence, calling simple_recursive_removal() on the top dentry would clean up all the children dentries as well. Doing it his way cleans up the code quite a bit!

fs/tracefs/event_inode.c | 77 +++++++++++++++++++++++----------------- fs/tracefs/internal.h | 2 -- 2 files changed, 44 insertions(+), 35 deletions(-)

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c index 0087a3f455f1..f8a594a50ae6 100644 --- a/fs/tracefs/event_inode.c +++ b/fs/tracefs/event_inode.c @@ -967,30 +967,29 @@ static void unhook_dentry(struct dentry *dentry) { if (!dentry) return; - - /* Keep the dentry from being freed yet (see eventfs_workfn()) */ + /* + * Need to add a reference to the dentry that is expected by + * simple_recursive_removal(), which will include a dput(). + */ dget(dentry);

- dentry->d_fsdata = NULL; - d_invalidate(dentry); - mutex_lock(&eventfs_mutex); - /* dentry should now have at least a single reference */ - WARN_ONCE((int)d_count(dentry) < 1, - "dentry %px (%s) less than one reference (%d) after invalidate\n", - dentry, dentry->d_name.name, d_count(dentry)); - mutex_unlock(&eventfs_mutex); + /* + * Also add a reference for the dput() in eventfs_workfn(). + * That is required as that dput() will free the ei after + * the SRCU grace period is over. + */ + dget(dentry); }

/** * eventfs_remove_rec - remove eventfs dir or file from list * @ei: eventfs_inode to be removed. - * @head: the list head to place the deleted @ei and children * @level: prevent recursion from going more than 3 levels deep. * * This function recursively removes eventfs_inodes which * contains info of files and/or directories. */ -static void eventfs_remove_rec(struct eventfs_inode *ei, struct list_head *head, int level) +static void eventfs_remove_rec(struct eventfs_inode *ei, int level) { struct eventfs_inode *ei_child;

@@ -1009,13 +1008,26 @@ static void eventfs_remove_rec(struct eventfs_inode *ei, struct list_head *head, /* search for nested folders or files */ list_for_each_entry_srcu(ei_child, &ei->children, list, lockdep_is_held(&eventfs_mutex)) { - eventfs_remove_rec(ei_child, head, level + 1); + /* Children only have dentry if parent does */ + WARN_ON_ONCE(ei_child->dentry && !ei->dentry); + eventfs_remove_rec(ei_child, level + 1); }

+ ei->is_freed = 1;

+ for (int i = 0; i < ei->nr_entries; i++) { + if (ei->d_children[i]) { + /* Children only have dentry if parent does */ + WARN_ON_ONCE(!ei->dentry); + unhook_dentry(ei->d_children[i]); + } + } + + unhook_dentry(ei->dentry); + list_del_rcu(&ei->list); - list_add_tail(&ei->del_list, head); + call_srcu(&eventfs_srcu, &ei->rcu, free_rcu_ei); }

/** @@ -1026,30 +1038,22 @@ static void eventfs_remove_rec(struct eventfs_inode *ei, struct list_head *head, */ void eventfs_remove_dir(struct eventfs_inode *ei) { - struct eventfs_inode *tmp; - LIST_HEAD(ei_del_list); + struct dentry *dentry;

if (!ei) return;

- /* - * Move the deleted eventfs_inodes onto the ei_del_list - * which will also set the is_freed value. Note, this has to be - * done under the eventfs_mutex, but the deletions of - * the dentries must be done outside the eventfs_mutex. - * Hence moving them to this temporary list. - */ mutex_lock(&eventfs_mutex); - eventfs_remove_rec(ei, &ei_del_list, 0); + dentry = ei->dentry; + eventfs_remove_rec(ei, 0); mutex_unlock(&eventfs_mutex);

- list_for_each_entry_safe(ei, tmp, &ei_del_list, del_list) { - for (int i = 0; i < ei->nr_entries; i++) - unhook_dentry(ei->d_children[i]); - unhook_dentry(ei->dentry); - list_del(&ei->del_list); - call_srcu(&eventfs_srcu, &ei->rcu, free_rcu_ei); - } + /* + * If any of the ei children has a dentry, then the ei itself + * must have a dentry. + */ + if (dentry) + simple_recursive_removal(dentry, NULL); }

/** @@ -1060,10 +1064,17 @@ void eventfs_remove_dir(struct eventfs_inode *ei) */ void eventfs_remove_events_dir(struct eventfs_inode *ei) { - struct dentry *dentry = ei->dentry; + struct dentry *dentry;

+ dentry = ei->dentry; eventfs_remove_dir(ei);

- /* Matches the dget() from eventfs_create_events_dir() */ + /* + * Matches the dget() done by tracefs_start_creating() + * in eventfs_create_events_dir() when it the dentry was + * created. In other words, it's a normal dentry that + * sticks around while the other ei->dentry are created + * and destroyed dynamically. + */ dput(dentry); } diff --git a/fs/tracefs/internal.h b/fs/tracefs/internal.h index 06a1f220b901..ccee18ca66c7 100644 --- a/fs/tracefs/internal.h +++ b/fs/tracefs/internal.h @@ -55,12 +55,10 @@ struct eventfs_inode { /* * Union - used for deletion * @llist: for calling dput() if needed after RCU - * @del_list: list of eventfs_inode to delete * @rcu: eventfs_inode to delete in RCU */ union { struct llist_node llist; - struct list_head del_list; struct rcu_head rcu; }; unsigned int is_freed:1;