fs: drop assert in file_seek_cur_needs_f_lock

The assert in function file_seek_cur_needs_f_lock() can be triggered very
easily because there are many users of vfs_llseek() (such as overlayfs)
that do their custom locking around llseek instead of relying on
fdget_pos(). Just drop the overzealous assertion.

Fixes: da06e3c ("fs: don't needlessly acquire f_lock")
Suggested-by: Jan Kara <[email protected]>
Suggested-by: Mateusz Guzik <[email protected]>
Signed-off-by: Luis Henriques <[email protected]>
Link: https://lore.kernel.org/[email protected]
Signed-off-by: Christian Brauner <[email protected]>

Author: luis-henrix

fs/file.c

@@ -1198,8 +1198,12 @@ bool file_seek_cur_needs_f_lock(struct file *file)
 	if (!(file->f_mode & FMODE_ATOMIC_POS) && !file->f_op->iterate_shared)
 		return false;
 
-	VFS_WARN_ON_ONCE((file_count(file) > 1) &&
-			 !mutex_is_locked(&file->f_pos_lock));
+	/*
+	 * Note that we are not guaranteed to be called after fdget_pos() on
+	 * this file obj, in which case the caller is expected to provide the
+	 * appropriate locking.
+	 */
+
 	return true;
 }