file: massage cleanup of files that failed to open

A file that has never gotten FMODE_OPENED will never have RCU-accessed
references, its final fput() is equivalent to file_free() and if it
doesn't have FMODE_BACKING either, it can be done from any context and
won't need task_work treatment.

Now that we have SLAB_TYPESAFE_BY_RCU we can simplify this and have
other callers benefit. All of that can be achieved easier is to make
fput() recoginze that case and call file_free() directly.

No need to introduce a special primitive for that. It also allowed
things like failing dentry_open() could benefit from that as well.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
[Christian Brauner <brauner@kernel.org>: massage commit message]
Link: https://lore.kernel.org/r/20231126020834.GC38156@ZenIV
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: Al Viro

fs/file_table.c

@@ -75,18 +75,6 @@ static inline void file_free(struct file *f)
 	}
 }
 
-void release_empty_file(struct file *f)
-{
-	WARN_ON_ONCE(f->f_mode & (FMODE_BACKING | FMODE_OPENED));
-	if (atomic_long_dec_and_test(&f->f_count)) {
-		security_file_free(f);
-		put_cred(f->f_cred);
-		if (likely(!(f->f_mode & FMODE_NOACCOUNT)))
-			percpu_counter_dec(&nr_files);
-		kmem_cache_free(filp_cachep, f);
-	}
-}
-
 /*
  * Return the total number of open files in the system
  */
@@ -445,6 +433,10 @@ void fput(struct file *file)
 	if (atomic_long_dec_and_test(&file->f_count)) {
 		struct task_struct *task = current;
 
+		if (unlikely(!(file->f_mode & (FMODE_BACKING | FMODE_OPENED)))) {
+			file_free(file);
+			return;
+		}
 		if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) {
 			init_task_work(&file->f_rcuhead, ____fput);
 			if (!task_work_add(task, &file->f_rcuhead, TWA_RESUME))

fs/internal.h

@@ -94,7 +94,6 @@ extern void chroot_fs_refs(const struct path *, const struct path *);
 struct file *alloc_empty_file(int flags, const struct cred *cred);
 struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred);
 struct file *alloc_empty_backing_file(int flags, const struct cred *cred);
-void release_empty_file(struct file *f);
 
 static inline void file_put_write_access(struct file *file)
 {

fs/namei.c

@@ -3785,10 +3785,7 @@ static struct file *path_openat(struct nameidata *nd,
 		WARN_ON(1);
 		error = -EINVAL;
 	}
-	if (unlikely(file->f_mode & FMODE_OPENED))
-		fput(file);
-	else
-		release_empty_file(file);
+	fput(file);
 	if (error == -EOPENSTALE) {
 		if (flags & LOOKUP_RCU)
 			error = -ECHILD;