From 6cf41fcfe099b61b4e3ea7dbe04a906f4c904822 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Thu, 5 Oct 2023 19:08:35 +0200 Subject: backing file: free directly Backing files as used by overlayfs are never installed into file descriptor tables and are explicitly documented as such. They aren't subject to rcu access conditions like regular files are. Their lifetime is bound to the lifetime of the overlayfs file, i.e., they're stashed in ovl_file->private_data and go away otherwise. If they're set as vma->vm_file - which is their main purpose - then they're subject to regular refcount rules and vma->vm_file can't be installed into an fdtable after having been set. All in all I don't see any need for rcu delay here. So free it directly. This all hinges on such hybrid beasts to never actually be installed into fdtables which - as mentioned before - is not allowed. So add an explicit WARN_ON_ONCE() so we catch any case where someone is suddenly trying to install one of those things into a file descriptor table so we can have a nice long chat with them. Link: https://lore.kernel.org/r/20231005-sakralbau-wappnen-f5c31755ed70@brauner Acked-by: Linus Torvalds Signed-off-by: Christian Brauner --- fs/file.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'fs/file.c') diff --git a/fs/file.c b/fs/file.c index 4eb026631673..1a475d7d636e 100644 --- a/fs/file.c +++ b/fs/file.c @@ -604,6 +604,9 @@ void fd_install(unsigned int fd, struct file *file) struct files_struct *files = current->files; struct fdtable *fdt; + if (WARN_ON_ONCE(unlikely(file->f_mode & FMODE_BACKING))) + return; + rcu_read_lock_sched(); if (unlikely(files->resize_in_progress)) { -- cgit