fork: add kernel_clone_args flag to not dup/clone files

Each vhost device gets a thread that is used to perform IO and management
operations. Instead of a thread that is accessing a device, the thread is
part of the device, so when it creates a thread using a helper based on
copy_process we can't dup or clone the parent's files/FDS because it
would do an extra increment on ourself.

Later, when we do:

Qemu process exits:
        do_exit -> exit_files -> put_files_struct -> close_files

we would leak the device's resources because of that extra refcount
on the fd or file_struct.

This patch adds a no_files option so these worker threads can prevent
taking an extra refcount on themselves.

Signed-off-by: Mike Christie <[email protected]>
Acked-by: Christian Brauner <[email protected]>
Acked-by: Michael S. Tsirkin <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: Christian Brauner (Microsoft) <[email protected]>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index 2950e83d5382..4f816048794f 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -28,6 +28,7 @@ struct kernel_clone_args {
 	u32 kthread:1;
 	u32 io_thread:1;
 	u32 user_worker:1;
+	u32 no_files:1;
 	unsigned long stack;
 	unsigned long stack_size;
 	unsigned long tls;