Merge branch 'vfs.file'

Bring in the changes to the file infrastructure for this cycle. Mostly
cleanups and some performance tweaks.

* file: remove __receive_fd()
* file: stop exposing receive_fd_user()
* fs: replace f_rcuhead with f_task_work
* file: remove pointless wrapper
* file: s/close_fd_get_file()/file_close_fd()/g
* Improve __fget_files_rcu() code generation (and thus __fget_light())
* file: massage cleanup of files that failed to open

Signed-off-by: Christian Brauner <[email protected]>

drivers/android/binder.c

@@ -1921,7 +1921,7 @@ static void binder_deferred_fd_close(int fd)
 	if (!twcb)
 		return;
 	init_task_work(&twcb->twork, binder_do_fd_close);
-	twcb->file = close_fd_get_file(fd);
+	twcb->file = file_close_fd(fd);
 	if (twcb->file) {
 		// pin it until binder_do_fd_close(); see comments there
 		get_file(twcb->file);

drivers/vdpa/vdpa_user/vduse_dev.c

@@ -1157,7 +1157,7 @@ static long vduse_dev_ioctl(struct file *file, unsigned int cmd,
 			fput(f);
 			break;
 		}
-		ret = receive_fd(f, perm_to_file_flags(entry.perm));
+		ret = receive_fd(f, NULL, perm_to_file_flags(entry.perm));
 		fput(f);
 		break;
 	}

fs/file.c

@@ -629,19 +629,23 @@ void fd_install(unsigned int fd, struct file *file)
 EXPORT_SYMBOL(fd_install);
 
 /**
- * pick_file - return file associatd with fd
+ * file_close_fd_locked - return file associated with fd
  * @files: file struct to retrieve file from
  * @fd: file descriptor to retrieve file for
  *
+ * Doesn't take a separate reference count.
+ *
  * Context: files_lock must be held.
  *
  * Returns: The file associated with @fd (NULL if @fd is not open)
  */
-static struct file *pick_file(struct files_struct *files, unsigned fd)
+struct file *file_close_fd_locked(struct files_struct *files, unsigned fd)
 {
 	struct fdtable *fdt = files_fdtable(files);
 	struct file *file;
 
+	lockdep_assert_held(&files->file_lock);
+
 	if (fd >= fdt->max_fds)
 		return NULL;
 
@@ -660,7 +664,7 @@ int close_fd(unsigned fd)
 	struct file *file;
 
 	spin_lock(&files->file_lock);
-	file = pick_file(files, fd);
+	file = file_close_fd_locked(files, fd);
 	spin_unlock(&files->file_lock);
 	if (!file)
 		return -EBADF;
@@ -707,7 +711,7 @@ static inline void __range_close(struct files_struct *files, unsigned int fd,
 	max_fd = min(max_fd, n);
 
 	for (; fd <= max_fd; fd++) {
-		file = pick_file(files, fd);
+		file = file_close_fd_locked(files, fd);
 		if (file) {
 			spin_unlock(&files->file_lock);
 			filp_close(file, files);
@@ -795,26 +799,21 @@ int __close_range(unsigned fd, unsigned max_fd, unsigned int flags)
 	return 0;
 }
 
-/*
- * See close_fd_get_file() below, this variant assumes current->files->file_lock
- * is held.
- */
-struct file *__close_fd_get_file(unsigned int fd)
-{
-	return pick_file(current->files, fd);
-}
-
-/*
- * variant of close_fd that gets a ref on the file for later fput.
- * The caller must ensure that filp_close() called on the file.
+/**
+ * file_close_fd - return file associated with fd
+ * @fd: file descriptor to retrieve file for
+ *
+ * Doesn't take a separate reference count.
+ *
+ * Returns: The file associated with @fd (NULL if @fd is not open)
  */
-struct file *close_fd_get_file(unsigned int fd)
+struct file *file_close_fd(unsigned int fd)
 {
 	struct files_struct *files = current->files;
 	struct file *file;
 
 	spin_lock(&files->file_lock);
-	file = pick_file(files, fd);
+	file = file_close_fd_locked(files, fd);
 	spin_unlock(&files->file_lock);
 
 	return file;
@@ -959,39 +958,54 @@ static inline struct file *__fget_files_rcu(struct files_struct *files,
 		struct file *file;
 		struct fdtable *fdt = rcu_dereference_raw(files->fdt);
 		struct file __rcu **fdentry;
+		unsigned long nospec_mask;
 
-		if (unlikely(fd >= fdt->max_fds))
-			return NULL;
-
-		fdentry = fdt->fd + array_index_nospec(fd, fdt->max_fds);
+		/* Mask is a 0 for invalid fd's, ~0 for valid ones */
+		nospec_mask = array_index_mask_nospec(fd, fdt->max_fds);
 
 		/*
-		 * Ok, we have a file pointer. However, because we do
-		 * this all locklessly under RCU, we may be racing with
-		 * that file being closed.
-		 *
-		 * Such a race can take two forms:
-		 *
-		 *  (a) the file ref already went down to zero and the
-		 *      file hasn't been reused yet or the file count
-		 *      isn't zero but the file has already been reused.
+		 * fdentry points to the 'fd' offset, or fdt->fd[0].
+		 * Loading from fdt->fd[0] is always safe, because the
+		 * array always exists.
 		 */
-		file = __get_file_rcu(fdentry);
+		fdentry = fdt->fd + (fd & nospec_mask);
+
+		/* Do the load, then mask any invalid result */
+		file = rcu_dereference_raw(*fdentry);
+		file = (void *)(nospec_mask & (unsigned long)file);
 		if (unlikely(!file))
 			return NULL;
 
-		if (unlikely(IS_ERR(file)))
+		/*
+		 * Ok, we have a file pointer that was valid at
+		 * some point, but it might have become stale since.
+		 *
+		 * We need to confirm it by incrementing the refcount
+		 * and then check the lookup again.
+		 *
+		 * atomic_long_inc_not_zero() gives us a full memory
+		 * barrier. We only really need an 'acquire' one to
+		 * protect the loads below, but we don't have that.
+		 */
+		if (unlikely(!atomic_long_inc_not_zero(&file->f_count)))
 			continue;
 
 		/*
+		 * Such a race can take two forms:
+		 *
+		 *  (a) the file ref already went down to zero and the
+		 *      file hasn't been reused yet or the file count
+		 *      isn't zero but the file has already been reused.
+		 *
 		 *  (b) the file table entry has changed under us.
 		 *       Note that we don't need to re-check the 'fdt->fd'
 		 *       pointer having changed, because it always goes
 		 *       hand-in-hand with 'fdt'.
 		 *
 		 * If so, we need to put our ref and try again.
 		 */
-		if (unlikely(rcu_dereference_raw(files->fdt) != fdt)) {
+		if (unlikely(file != rcu_dereference_raw(*fdentry)) ||
+		    unlikely(rcu_dereference_raw(files->fdt) != fdt)) {
 			fput(file);
 			continue;
 		}
@@ -1128,13 +1142,13 @@ static unsigned long __fget_light(unsigned int fd, fmode_t mask)
 	 * atomic_read_acquire() pairs with atomic_dec_and_test() in
 	 * put_files_struct().
 	 */
-	if (atomic_read_acquire(&files->count) == 1) {
+	if (likely(atomic_read_acquire(&files->count) == 1)) {
 		file = files_lookup_fd_raw(files, fd);
 		if (!file || unlikely(file->f_mode & mask))
 			return 0;
 		return (unsigned long)file;
 	} else {
-		file = __fget(fd, mask);
+		file = __fget_files(files, fd, mask);
 		if (!file)
 			return 0;
 		return FDPUT_FPUT | (unsigned long)file;
@@ -1282,7 +1296,7 @@ int replace_fd(unsigned fd, struct file *file, unsigned flags)
 }
 
 /**
- * __receive_fd() - Install received file into file descriptor table
+ * receive_fd() - Install received file into file descriptor table
  * @file: struct file that was received from another process
  * @ufd: __user pointer to write new fd number to
  * @o_flags: the O_* flags to apply to the new fd entry
@@ -1296,7 +1310,7 @@ int replace_fd(unsigned fd, struct file *file, unsigned flags)
  *
  * Returns newly install fd or -ve on error.
  */
-int __receive_fd(struct file *file, int __user *ufd, unsigned int o_flags)
+int receive_fd(struct file *file, int __user *ufd, unsigned int o_flags)
 {
 	int new_fd;
 	int error;
@@ -1321,6 +1335,7 @@ int __receive_fd(struct file *file, int __user *ufd, unsigned int o_flags)
 	__receive_sock(file);
 	return new_fd;
 }
+EXPORT_SYMBOL_GPL(receive_fd);
 
 int receive_fd_replace(int new_fd, struct file *file, unsigned int o_flags)
 {
@@ -1336,12 +1351,6 @@ int receive_fd_replace(int new_fd, struct file *file, unsigned int o_flags)
 	return new_fd;
 }
 
-int receive_fd(struct file *file, unsigned int o_flags)
-{
-	return __receive_fd(file, NULL, o_flags);
-}
-EXPORT_SYMBOL_GPL(receive_fd);
-
 static int ksys_dup3(unsigned int oldfd, unsigned int newfd, int flags)
 {
 	int err = -EBADF;

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
  */
@@ -419,7 +407,7 @@ static void delayed_fput(struct work_struct *unused)
 
 static void ____fput(struct callback_head *work)
 {
-	__fput(container_of(work, struct file, f_rcuhead));
+	__fput(container_of(work, struct file, f_task_work));
 }
 
 /*
@@ -445,9 +433,13 @@ 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))
+			init_task_work(&file->f_task_work, ____fput);
+			if (!task_work_add(task, &file->f_task_work, TWA_RESUME))
 				return;
 			/*
 			 * After this task has run exit_task_work(),

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)
 {
@@ -180,7 +179,7 @@ extern struct file *do_file_open_root(const struct path *,
 		const char *, const struct open_flags *);
 extern struct open_how build_open_how(int flags, umode_t mode);
 extern int build_open_flags(const struct open_how *how, struct open_flags *op);
-extern struct file *__close_fd_get_file(unsigned int fd);
+struct file *file_close_fd_locked(struct files_struct *files, unsigned fd);
 
 long do_sys_ftruncate(unsigned int fd, loff_t length, int small);
 int chmod_common(const struct path *path, umode_t mode);

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;

fs/open.c

@@ -1578,7 +1578,7 @@ SYSCALL_DEFINE1(close, unsigned int, fd)
 	int retval;
 	struct file *file;
 
-	file = close_fd_get_file(fd);
+	file = file_close_fd(fd);
 	if (!file)
 		return -EBADF;
 

include/linux/fdtable.h

@@ -83,12 +83,17 @@ struct dentry;
 static inline struct file *files_lookup_fd_raw(struct files_struct *files, unsigned int fd)
 {
 	struct fdtable *fdt = rcu_dereference_raw(files->fdt);
-
-	if (fd < fdt->max_fds) {
-		fd = array_index_nospec(fd, fdt->max_fds);
-		return rcu_dereference_raw(fdt->fd[fd]);
-	}
-	return NULL;
+	unsigned long mask = array_index_mask_nospec(fd, fdt->max_fds);
+	struct file *needs_masking;
+
+	/*
+	 * 'mask' is zero for an out-of-bounds fd, all ones for ok.
+	 * 'fd&mask' is 'fd' for ok, or 0 for out of bounds.
+	 *
+	 * Accessing fdt->fd[0] is ok, but needs masking of the result.
+	 */
+	needs_masking = rcu_dereference_raw(fdt->fd[fd&mask]);
+	return (struct file *)(mask & (unsigned long)needs_masking);
 }
 
 static inline struct file *files_lookup_fd_locked(struct files_struct *files, unsigned int fd)
@@ -114,7 +119,7 @@ int iterate_fd(struct files_struct *, unsigned,
 
 extern int close_fd(unsigned int fd);
 extern int __close_range(unsigned int fd, unsigned int max_fd, unsigned int flags);
-extern struct file *close_fd_get_file(unsigned int fd);
+extern struct file *file_close_fd(unsigned int fd);
 extern int unshare_fd(unsigned long unshare_flags, unsigned int max_fds,
 		      struct files_struct **new_fdp);
 

include/linux/file.h

@@ -96,18 +96,8 @@ DEFINE_CLASS(get_unused_fd, int, if (_T >= 0) put_unused_fd(_T),
 
 extern void fd_install(unsigned int fd, struct file *file);
 
-extern int __receive_fd(struct file *file, int __user *ufd,
-			unsigned int o_flags);
+int receive_fd(struct file *file, int __user *ufd, unsigned int o_flags);
 
-extern int receive_fd(struct file *file, unsigned int o_flags);
-
-static inline int receive_fd_user(struct file *file, int __user *ufd,
-				  unsigned int o_flags)
-{
-	if (ufd == NULL)
-		return -EFAULT;
-	return __receive_fd(file, ufd, o_flags);
-}
 int receive_fd_replace(int new_fd, struct file *file, unsigned int o_flags);
 
 extern void flush_delayed_fput(void);

include/linux/fs.h

@@ -991,8 +991,10 @@ static inline int ra_has_index(struct file_ra_state *ra, pgoff_t index)
  */
 struct file {
 	union {
+		/* fput() uses task work when closing and freeing file (default). */
+		struct callback_head 	f_task_work;
+		/* fput() must use workqueue (most kernel threads). */
 		struct llist_node	f_llist;
-		struct rcu_head 	f_rcuhead;
 		unsigned int 		f_iocb_flags;
 	};
 

include/net/scm.h

@@ -5,6 +5,7 @@
 #include <linux/limits.h>
 #include <linux/net.h>
 #include <linux/cred.h>
+#include <linux/file.h>
 #include <linux/security.h>
 #include <linux/pid.h>
 #include <linux/nsproxy.h>
@@ -208,5 +209,13 @@ static inline void scm_recv_unix(struct socket *sock, struct msghdr *msg,
 	scm_destroy_cred(scm);
 }
 
+static inline int scm_recv_one_fd(struct file *f, int __user *ufd,
+				  unsigned int flags)
+{
+	if (!ufd)
+		return -EFAULT;
+	return receive_fd(f, ufd, flags);
+}
+
 #endif /* __LINUX_NET_SCM_H */