Unverified Commit 11f3f500 authored by Mike Christie's avatar Mike Christie Committed by Christian Brauner (Microsoft)
Browse files

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: default avatarMike Christie <michael.christie@oracle.com>
Acked-by: default avatarChristian Brauner <brauner@kernel.org>
Acked-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarChristian Brauner (Microsoft) <brauner@kernel.org>
parent 54e6842d

include/linux/sched/task.h

+1 −0
Original line number Diff line number Diff line
@@ -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;

kernel/fork.c

+8 −2
Original line number Diff line number Diff line
@@ -1627,7 +1627,8 @@ static int copy_fs(unsigned long clone_flags, struct task_struct *tsk) 
	return 0;

}



static int copy_files(unsigned long clone_flags, struct task_struct *tsk)

static int copy_files(unsigned long clone_flags, struct task_struct *tsk,

		      int no_files)

{

	struct files_struct *oldf, *newf;

	int error = 0;
@@ -1639,6 +1640,11 @@ static int copy_files(unsigned long clone_flags, struct task_struct *tsk) 
	if (!oldf)

		goto out;



	if (no_files) {

		tsk->files = NULL;

		goto out;

	}



	if (clone_flags & CLONE_FILES) {

		atomic_inc(&oldf->count);

		goto out;
@@ -2259,7 +2265,7 @@ static __latent_entropy struct task_struct *copy_process( 
	retval = copy_semundo(clone_flags, p);

	if (retval)

		goto bad_fork_cleanup_security;

	retval = copy_files(clone_flags, p);

	retval = copy_files(clone_flags, p, args->no_files);

	if (retval)

		goto bad_fork_cleanup_semundo;

	retval = copy_fs(clone_flags, p);