Re: [PATCH 2/3] kernel/fork, cred.c: allow copy_process to take user
From: Mike Christie <michael.christie@oracle.com>
Date: 2021-06-29 16:54:03
On 6/29/21 8:04 AM, Christian Brauner wrote:
On Wed, Jun 23, 2021 at 10:08:03PM -0500, Mike Christie wrote:quoted
This allows kthread to pass copy_process the user we want to check for the RLIMIT_NPROC limit for and also charge for the new process. It will be used by vhost where userspace has that driver create threads but the kthreadd thread is checked/charged. Signed-off-by: Mike Christie <michael.christie@oracle.com> --- include/linux/cred.h | 3 ++- kernel/cred.c | 7 ++++--- kernel/fork.c | 12 +++++++----- 3 files changed, 13 insertions(+), 9 deletions(-)diff --git a/include/linux/cred.h b/include/linux/cred.h index 14971322e1a0..9a2c1398cdd4 100644 --- a/include/linux/cred.h +++ b/include/linux/cred.h@@ -153,7 +153,8 @@ struct cred { extern void __put_cred(struct cred *); extern void exit_creds(struct task_struct *); -extern int copy_creds(struct task_struct *, unsigned long); +extern int copy_creds(struct task_struct *, unsigned long, + struct user_struct *); extern const struct cred *get_task_cred(struct task_struct *); extern struct cred *cred_alloc_blank(void); extern struct cred *prepare_creds(void);diff --git a/kernel/cred.c b/kernel/cred.c index e1d274cd741b..e006aafa8f05 100644 --- a/kernel/cred.c +++ b/kernel/cred.c@@ -330,7 +330,8 @@ struct cred *prepare_exec_creds(void) * The new process gets the current process's subjective credentials as its * objective and subjective credentials */ -int copy_creds(struct task_struct *p, unsigned long clone_flags) +int copy_creds(struct task_struct *p, unsigned long clone_flags, + struct user_struct *user) { struct cred *new; int ret;@@ -351,7 +352,7 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags) kdebug("share_creds(%p{%d,%d})", p->cred, atomic_read(&p->cred->usage), read_cred_subscribers(p->cred)); - atomic_inc(&p->cred->user->processes); + atomic_inc(&user->processes);Hey Mike, This won't work anymore since this has moved into ucounts. So in v5.14 atomic_inc(&p->cred->user->processes); will have been replaced by inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
Will do.
From what I can see from your code vhost will always create this kthread for current. So you could e.g. add an internal flag/bitfield entry to struct kernel_clone_args that you can use to tell copy_creds() that you want to charge this thread against current's process limit.
If I understood you, I don't think a flag/bit will work. When vhost does a kthread call we do kthread_create -> __kthread_create_on_node. This creates a tmp kthread_create_info struct and adds it to the kthread_create_list list. It then wakes up the kthreadd thread. kthreadd will then loop over the list, and do the: kernel_thread -> kernel_clone -> copy_process -> copy_creds So copy_creds sees current == kthreadd. I think I would have to add a task_struct pointer to kernel_clone_args and kthread_create_info. If copy_creds sees kernel_clone_args->user_task then it would use that. _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization