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    SubjectRe: [PATCH 01/10] clone: add CLONE_PIDFD
    On Fri, Dec 04, 2020 at 02:31:55AM +0800, Wen Yang wrote:
    > From: Christian Brauner <christian@brauner.io>
    >
    > [ Upstream commit b3e5838252665ee4cfa76b82bdf1198dca81e5be ]
    >
    > This patchset makes it possible to retrieve pid file descriptors at
    > process creation time by introducing the new flag CLONE_PIDFD to the
    > clone() system call. Linus originally suggested to implement this as a
    > new flag to clone() instead of making it a separate system call. As
    > spotted by Linus, there is exactly one bit for clone() left.
    >
    > CLONE_PIDFD creates file descriptors based on the anonymous inode
    > implementation in the kernel that will also be used to implement the new
    > mount api. They serve as a simple opaque handle on pids. Logically,
    > this makes it possible to interpret a pidfd differently, narrowing or
    > widening the scope of various operations (e.g. signal sending). Thus, a
    > pidfd cannot just refer to a tgid, but also a tid, or in theory - given
    > appropriate flag arguments in relevant syscalls - a process group or
    > session. A pidfd does not represent a privilege. This does not imply it
    > cannot ever be that way but for now this is not the case.
    >
    > A pidfd comes with additional information in fdinfo if the kernel supports
    > procfs. The fdinfo file contains the pid of the process in the callers
    > pid namespace in the same format as the procfs status file, i.e. "Pid:\t%d".
    >
    > As suggested by Oleg, with CLONE_PIDFD the pidfd is returned in the
    > parent_tidptr argument of clone. This has the advantage that we can
    > give back the associated pid and the pidfd at the same time.
    >
    > To remove worries about missing metadata access this patchset comes with
    > a sample program that illustrates how a combination of CLONE_PIDFD, and
    > pidfd_send_signal() can be used to gain race-free access to process
    > metadata through /proc/<pid>. The sample program can easily be
    > translated into a helper that would be suitable for inclusion in libc so
    > that users don't have to worry about writing it themselves.
    >
    > Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
    > Signed-off-by: Christian Brauner <christian@brauner.io>
    > Co-developed-by: Jann Horn <jannh@google.com>
    > Signed-off-by: Jann Horn <jannh@google.com>
    > Reviewed-by: Oleg Nesterov <oleg@redhat.com>
    > Cc: Arnd Bergmann <arnd@arndb.de>
    > Cc: "Eric W. Biederman" <ebiederm@xmission.com>
    > Cc: Kees Cook <keescook@chromium.org>
    > Cc: Thomas Gleixner <tglx@linutronix.de>
    > Cc: David Howells <dhowells@redhat.com>
    > Cc: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
    > Cc: Andy Lutomirsky <luto@kernel.org>
    > Cc: Andrew Morton <akpm@linux-foundation.org>
    > Cc: Aleksa Sarai <cyphar@cyphar.com>
    > Cc: Linus Torvalds <torvalds@linux-foundation.org>
    > Cc: Al Viro <viro@zeniv.linux.org.uk>
    > Cc: <stable@vger.kernel.org> # 4.9.x
    > (clone: fix up cherry-pick conflicts for b3e583825266)
    > Signed-off-by: Wen Yang <wenyang@linux.alibaba.com>
    > ---
    > include/linux/pid.h | 1 +
    > include/uapi/linux/sched.h | 1 +
    > kernel/fork.c | 119 +++++++++++++++++++++++++++++++++++++++++++--
    > 3 files changed, 117 insertions(+), 4 deletions(-)
    >
    > diff --git a/include/linux/pid.h b/include/linux/pid.h
    > index 97b745d..7599a78 100644
    > --- a/include/linux/pid.h
    > +++ b/include/linux/pid.h
    > @@ -73,6 +73,7 @@ struct pid_link
    > struct hlist_node node;
    > struct pid *pid;
    > };
    > +extern const struct file_operations pidfd_fops;
    >
    > static inline struct pid *get_pid(struct pid *pid)
    > {
    > diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
    > index 5f0fe01..ed6e31d 100644
    > --- a/include/uapi/linux/sched.h
    > +++ b/include/uapi/linux/sched.h
    > @@ -9,6 +9,7 @@
    > #define CLONE_FS 0x00000200 /* set if fs info shared between processes */
    > #define CLONE_FILES 0x00000400 /* set if open files shared between processes */
    > #define CLONE_SIGHAND 0x00000800 /* set if signal handlers and blocked signals shared */
    > +#define CLONE_PIDFD 0x00001000 /* set if a pidfd should be placed in parent */
    > #define CLONE_PTRACE 0x00002000 /* set if we want to let tracing continue on the child too */
    > #define CLONE_VFORK 0x00004000 /* set if the parent wants the child to wake it up on mm_release */
    > #define CLONE_PARENT 0x00008000 /* set if we want to have the same parent as the cloner */
    > diff --git a/kernel/fork.c b/kernel/fork.c
    > index b64efec..076297a 100644
    > --- a/kernel/fork.c
    > +++ b/kernel/fork.c
    > @@ -11,7 +11,22 @@
    > * management can be a bitch. See 'mm/memory.c': 'copy_page_range()'
    > */
    >
    > +#include <linux/anon_inodes.h>
    > #include <linux/slab.h>
    > +#if 0
    > +#include <linux/sched/autogroup.h>
    > +#include <linux/sched/mm.h>
    > +#include <linux/sched/coredump.h>
    > +#include <linux/sched/user.h>
    > +#include <linux/sched/numa_balancing.h>
    > +#include <linux/sched/stat.h>
    > +#include <linux/sched/task.h>
    > +#include <linux/sched/task_stack.h>
    > +#include <linux/sched/cputime.h>
    > +#include <linux/seq_file.h>
    > +#include <linux/rtmutex.h>
    > +>>>>>>> b3e58382... clone: add CLONE_PIDFD
    > +#endif

    That looks odd :(

    Can you please refresh this patch series, and make sure it is correct
    and resend it?

    thanks,

    greg k-h

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