linux_dsm_epyc7002/include/linux/sched/task.h
Christian Brauner 7f192e3cd3
fork: add clone3
This adds the clone3 system call.

As mentioned several times already (cf. [7], [8]) here's the promised
patchset for clone3().

We recently merged the CLONE_PIDFD patchset (cf. [1]). It took the last
free flag from clone().

Independent of the CLONE_PIDFD patchset a time namespace has been discussed
at Linux Plumber Conference last year and has been sent out and reviewed
(cf. [5]). It is expected that it will go upstream in the not too distant
future. However, it relies on the addition of the CLONE_NEWTIME flag to
clone(). The only other good candidate - CLONE_DETACHED - is currently not
recyclable as we have identified at least two large or widely used
codebases that currently pass this flag (cf. [2], [3], and [4]). Given that
CLONE_PIDFD grabbed the last clone() flag the time namespace is effectively
blocked. clone3() has the advantage that it will unblock this patchset
again. In general, clone3() is extensible and allows for the implementation
of new features.

The idea is to keep clone3() very simple and close to the original clone(),
specifically, to keep on supporting old clone()-based workloads.
We know there have been various creative proposals how a new process
creation syscall or even api is supposed to look like. Some people even
going so far as to argue that the traditional fork()+exec() split should be
abandoned in favor of an in-kernel version of spawn(). Independent of
whether or not we personally think spawn() is a good idea this patchset has
and does not want to have anything to do with this.
One stance we take is that there's no real good alternative to
clone()+exec() and we need and want to support this model going forward;
independent of spawn().
The following requirements guided clone3():
- bump the number of available flags
- move arguments that are currently passed as separate arguments
  in clone() into a dedicated struct clone_args
  - choose a struct layout that is easy to handle on 32 and on 64 bit
  - choose a struct layout that is extensible
  - give new flags that currently need to abuse another flag's dedicated
    return argument in clone() their own dedicated return argument
    (e.g. CLONE_PIDFD)
  - use a separate kernel internal struct kernel_clone_args that is
    properly typed according to current kernel conventions in fork.c and is
    different from  the uapi struct clone_args
- port _do_fork() to use kernel_clone_args so that all process creation
  syscalls such as fork(), vfork(), clone(), and clone3() behave identical
  (Arnd suggested, that we can probably also port do_fork() itself in a
   separate patchset.)
- ease of transition for userspace from clone() to clone3()
  This very much means that we do *not* remove functionality that userspace
  currently relies on as the latter is a good way of creating a syscall
  that won't be adopted.
- do not try to be clever or complex: keep clone3() as dumb as possible

In accordance with Linus suggestions (cf. [11]), clone3() has the following
signature:

/* uapi */
struct clone_args {
        __aligned_u64 flags;
        __aligned_u64 pidfd;
        __aligned_u64 child_tid;
        __aligned_u64 parent_tid;
        __aligned_u64 exit_signal;
        __aligned_u64 stack;
        __aligned_u64 stack_size;
        __aligned_u64 tls;
};

/* kernel internal */
struct kernel_clone_args {
        u64 flags;
        int __user *pidfd;
        int __user *child_tid;
        int __user *parent_tid;
        int exit_signal;
        unsigned long stack;
        unsigned long stack_size;
        unsigned long tls;
};

long sys_clone3(struct clone_args __user *uargs, size_t size)

clone3() cleanly supports all of the supported flags from clone() and thus
all legacy workloads.
The advantage of sticking close to the old clone() is the low cost for
userspace to switch to this new api. Quite a lot of userspace apis (e.g.
pthreads) are based on the clone() syscall. With the new clone3() syscall
supporting all of the old workloads and opening up the ability to add new
features should make switching to it for userspace more appealing. In
essence, glibc can just write a simple wrapper to switch from clone() to
clone3().

There has been some interest in this patchset already. We have received a
patch from the CRIU corner for clone3() that would set the PID/TID of a
restored process without /proc/sys/kernel/ns_last_pid to eliminate a race.

/* User visible differences to legacy clone() */
- CLONE_DETACHED will cause EINVAL with clone3()
- CSIGNAL is deprecated
  It is superseeded by a dedicated "exit_signal" argument in struct
  clone_args freeing up space for additional flags.
  This is based on a suggestion from Andrei and Linus (cf. [9] and [10])

/* References */
[1]: b3e5838252
[2]: https://dxr.mozilla.org/mozilla-central/source/security/sandbox/linux/SandboxFilter.cpp#343
[3]: https://git.musl-libc.org/cgit/musl/tree/src/thread/pthread_create.c#n233
[4]: https://sources.debian.org/src/blcr/0.8.5-2.3/cr_module/cr_dump_self.c/?hl=740#L740
[5]: https://lore.kernel.org/lkml/20190425161416.26600-1-dima@arista.com/
[6]: https://lore.kernel.org/lkml/20190425161416.26600-2-dima@arista.com/
[7]: https://lore.kernel.org/lkml/CAHrFyr5HxpGXA2YrKza-oB-GGwJCqwPfyhD-Y5wbktWZdt0sGQ@mail.gmail.com/
[8]: https://lore.kernel.org/lkml/20190524102756.qjsjxukuq2f4t6bo@brauner.io/
[9]: https://lore.kernel.org/lkml/20190529222414.GA6492@gmail.com/
[10]: https://lore.kernel.org/lkml/CAHk-=whQP-Ykxi=zSYaV9iXsHsENa+2fdj-zYKwyeyed63Lsfw@mail.gmail.com/
[11]: https://lore.kernel.org/lkml/CAHk-=wieuV4hGwznPsX-8E0G2FKhx3NjZ9X3dTKh5zKd+iqOBw@mail.gmail.com/

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Christian Brauner <christian@brauner.io>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Serge Hallyn <serge@hallyn.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Pavel Emelyanov <xemul@virtuozzo.com>
Cc: Jann Horn <jannh@google.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Adrian Reber <adrian@lisas.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrei Vagin <avagin@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: linux-api@vger.kernel.org
2019-06-09 09:29:28 +02:00

172 lines
4.6 KiB
C

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_SCHED_TASK_H
#define _LINUX_SCHED_TASK_H
/*
* Interface between the scheduler and various task lifetime (fork()/exit())
* functionality:
*/
#include <linux/sched.h>
#include <linux/uaccess.h>
struct task_struct;
struct rusage;
union thread_union;
/* All the bits taken by the old clone syscall. */
#define CLONE_LEGACY_FLAGS 0xffffffffULL
struct kernel_clone_args {
u64 flags;
int __user *pidfd;
int __user *child_tid;
int __user *parent_tid;
int exit_signal;
unsigned long stack;
unsigned long stack_size;
unsigned long tls;
};
/*
* This serializes "schedule()" and also protects
* the run-queue from deletions/modifications (but
* _adding_ to the beginning of the run-queue has
* a separate lock).
*/
extern rwlock_t tasklist_lock;
extern spinlock_t mmlist_lock;
extern union thread_union init_thread_union;
extern struct task_struct init_task;
#ifdef CONFIG_PROVE_RCU
extern int lockdep_tasklist_lock_is_held(void);
#endif /* #ifdef CONFIG_PROVE_RCU */
extern asmlinkage void schedule_tail(struct task_struct *prev);
extern void init_idle(struct task_struct *idle, int cpu);
extern int sched_fork(unsigned long clone_flags, struct task_struct *p);
extern void sched_dead(struct task_struct *p);
void __noreturn do_task_dead(void);
extern void proc_caches_init(void);
extern void fork_init(void);
extern void release_task(struct task_struct * p);
#ifdef CONFIG_HAVE_COPY_THREAD_TLS
extern int copy_thread_tls(unsigned long, unsigned long, unsigned long,
struct task_struct *, unsigned long);
#else
extern int copy_thread(unsigned long, unsigned long, unsigned long,
struct task_struct *);
/* Architectures that haven't opted into copy_thread_tls get the tls argument
* via pt_regs, so ignore the tls argument passed via C. */
static inline int copy_thread_tls(
unsigned long clone_flags, unsigned long sp, unsigned long arg,
struct task_struct *p, unsigned long tls)
{
return copy_thread(clone_flags, sp, arg, p);
}
#endif
extern void flush_thread(void);
#ifdef CONFIG_HAVE_EXIT_THREAD
extern void exit_thread(struct task_struct *tsk);
#else
static inline void exit_thread(struct task_struct *tsk)
{
}
#endif
extern void do_group_exit(int);
extern void exit_files(struct task_struct *);
extern void exit_itimers(struct signal_struct *);
extern long _do_fork(struct kernel_clone_args *kargs);
extern long do_fork(unsigned long, unsigned long, unsigned long, int __user *, int __user *);
struct task_struct *fork_idle(int);
struct mm_struct *copy_init_mm(void);
extern pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags);
extern long kernel_wait4(pid_t, int __user *, int, struct rusage *);
extern void free_task(struct task_struct *tsk);
/* sched_exec is called by processes performing an exec */
#ifdef CONFIG_SMP
extern void sched_exec(void);
#else
#define sched_exec() {}
#endif
#define get_task_struct(tsk) do { refcount_inc(&(tsk)->usage); } while(0)
extern void __put_task_struct(struct task_struct *t);
static inline void put_task_struct(struct task_struct *t)
{
if (refcount_dec_and_test(&t->usage))
__put_task_struct(t);
}
struct task_struct *task_rcu_dereference(struct task_struct **ptask);
#ifdef CONFIG_ARCH_WANTS_DYNAMIC_TASK_STRUCT
extern int arch_task_struct_size __read_mostly;
#else
# define arch_task_struct_size (sizeof(struct task_struct))
#endif
#ifndef CONFIG_HAVE_ARCH_THREAD_STRUCT_WHITELIST
/*
* If an architecture has not declared a thread_struct whitelist we
* must assume something there may need to be copied to userspace.
*/
static inline void arch_thread_struct_whitelist(unsigned long *offset,
unsigned long *size)
{
*offset = 0;
/* Handle dynamically sized thread_struct. */
*size = arch_task_struct_size - offsetof(struct task_struct, thread);
}
#endif
#ifdef CONFIG_VMAP_STACK
static inline struct vm_struct *task_stack_vm_area(const struct task_struct *t)
{
return t->stack_vm_area;
}
#else
static inline struct vm_struct *task_stack_vm_area(const struct task_struct *t)
{
return NULL;
}
#endif
/*
* Protects ->fs, ->files, ->mm, ->group_info, ->comm, keyring
* subscriptions and synchronises with wait4(). Also used in procfs. Also
* pins the final release of task.io_context. Also protects ->cpuset and
* ->cgroup.subsys[]. And ->vfork_done.
*
* Nests both inside and outside of read_lock(&tasklist_lock).
* It must not be nested with write_lock_irq(&tasklist_lock),
* neither inside nor outside.
*/
static inline void task_lock(struct task_struct *p)
{
spin_lock(&p->alloc_lock);
}
static inline void task_unlock(struct task_struct *p)
{
spin_unlock(&p->alloc_lock);
}
#endif /* _LINUX_SCHED_TASK_H */