From: "Steven Rostedt (Google)" rostedt@goodmis.org
The directory link count in eventfs was somewhat bogus. It was only being updated when a directory child was being looked up and not on creation.
One solution would be to update in get_attr() the link count by iterating the ei->children list and then adding 2. But that could slow down simple stat() calls, especially if it's done on all directories in eventfs.
Another solution would be to add a parent pointer to the eventfs_inode and keep track of the number of sub directories it has on creation. But this adds overhead for something not really worthwhile.
The solution decided upon is to keep all directory links in eventfs as 1. This tells user space not to rely on the hard links of directories. Which in this case it shouldn't.
Link: https://lore.kernel.org/linux-trace-kernel/20240201002719.GS2087318@ZenIV/ Link: https://lore.kernel.org/linux-trace-kernel/20240201161617.339968298@goodmis....
Cc: stable@vger.kernel.org Cc: Linus Torvalds torvalds@linux-foundation.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 Fixes: c1504e510238 ("eventfs: Implement eventfs dir creation functions") Suggested-by: Al Viro viro@zeniv.linux.org.uk Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org (cherry picked from commit ca185770db914869ff9fe773bac5e0e5e4165b83) --- fs/tracefs/event_inode.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-)
diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c index 9e031e5a2713..110e8a272189 100644 --- a/fs/tracefs/event_inode.c +++ b/fs/tracefs/event_inode.c @@ -404,9 +404,7 @@ static struct dentry *lookup_dir_entry(struct dentry *dentry,
dentry->d_fsdata = get_ei(ei);
- inc_nlink(inode); d_add(dentry, inode); - inc_nlink(dentry->d_parent->d_inode); return NULL; }
@@ -769,9 +767,17 @@ struct eventfs_inode *eventfs_create_events_dir(const char *name, struct dentry
dentry->d_fsdata = get_ei(ei);
- /* directory inodes start off with i_nlink == 2 (for "." entry) */ - inc_nlink(inode); + /* + * Keep all eventfs directories with i_nlink == 1. + * Due to the dynamic nature of the dentry creations and not + * wanting to add a pointer to the parent eventfs_inode in the + * eventfs_inode structure, keeping the i_nlink in sync with the + * number of directories would cause too much complexity for + * something not worth much. Keeping directory links at 1 + * tells userspace not to trust the link number. + */ d_instantiate(dentry, inode); + /* The dentry of the "events" parent does keep track though */ inc_nlink(dentry->d_parent->d_inode); fsnotify_mkdir(dentry->d_parent->d_inode, dentry); tracefs_end_creating(dentry);