Re: [PATCH] kernel/signal: Signal-based pre-coredump notification

[Greg Kroah-Hartman]

On Fri, Oct 12, 2018 at 05:33:35PM -0700, Enke Chen wrote:
> For simplicity and consistency, this patch provides an implementation
> for signal-based fault notification prior to the coredump of a child
> process. A new prctl command, PR_SET_PREDUMP_SIG, is defined that can
> be used by an application to express its interest and to specify the
> signal (SIGCHLD or SIGUSR1 or SIGUSR2) for such a notification. A new
> signal code (si_code), CLD_PREDUMP, is also defined for SIGCHLD.
> 
> Background:
> 
> As the coredump of a process may take time, in certain time-sensitive
> applications it is necessary for a parent process (e.g., a process
> manager) to be notified of a child's imminent death before the coredump
> so that the parent process can act sooner, such as re-spawning an
> application process, or initiating a control-plane fail-over.
> 
> Currently there are two ways for a parent process to be notified of a
> child process's state change. One is to use the POSIX signal, and
> another is to use the kernel connector module. The specific events and
> actions are summarized as follows:
> 
> Process Event    POSIX Signal                Connector-based
> ----------------------------------------------------------------------
> ptrace_attach()  do_notify_parent_cldstop()  proc_ptrace_connector()
>                  SIGCHLD / CLD_STOPPED
> 
> ptrace_detach()  do_notify_parent_cldstop()  proc_ptrace_connector()
>                  SIGCHLD / CLD_CONTINUED
> 
> pre_coredump/    N/A                         proc_coredump_connector()
> get_signal()
> 
> post_coredump/   do_notify_parent()          proc_exit_connector()
> do_exit()        SIGCHLD / exit_signal
> ----------------------------------------------------------------------
> 
> As shown in the table, the signal-based pre-coredump notification is not
> currently available. In some cases using a connector-based notification
> can be quite complicated (e.g., when a process manager is written in shell
> scripts and thus is subject to certain inherent limitations), and a
> signal-based notification would be simpler and better suited.
> 
> Signed-off-by: Enke Chen <enkechen@xxxxxxxxx>
> ---
>  arch/x86/kernel/signal_compat.c    |  2 +-
>  include/linux/sched.h              |  4 ++
>  include/linux/signal.h             |  5 +++
>  include/uapi/asm-generic/siginfo.h |  3 +-
>  include/uapi/linux/prctl.h         |  4 ++
>  kernel/fork.c                      |  1 +
>  kernel/signal.c                    | 51 +++++++++++++++++++++++++
>  kernel/sys.c                       | 77 ++++++++++++++++++++++++++++++++++++++
>  8 files changed, 145 insertions(+), 2 deletions(-)

Shouldn't there also be a manpage update, and a kselftest added for this
new user/kernel api that is being created?

thanks,

greg k-h