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fork: add kernel_clone_args flag to not dup/clone files

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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 <michael.christie@oracle.com>
Acked-by: Christian Brauner <brauner@kernel.org>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
This commit is contained in:
Mike Christie 2023-03-10 16:03:27 -06:00 committed by Christian Brauner (Microsoft)
parent 54e6842d07
commit 11f3f500ec
No known key found for this signature in database
GPG Key ID: 91C61BC06578DCA2
2 changed files with 9 additions and 2 deletions
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1
include/linux/sched/task.h
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@ -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;

10
kernel/fork.c
View File

@ -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);