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    SubjectRe: [PATCH] kernel/signal: Signal-based pre-coredump notification
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    Hi, Greg:

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

    I will submit a patch for manpage update once the code is accepted.

    Regarding the kselftest, I am not sure. Once the prctl() is limited to
    self (which I will do), the logic would be pretty straightforward. Not
    sure if the selftest would add much value.

    Thanks. -- Enke

    On 10/12/18 11:40 PM, Greg Kroah-Hartman wrote:
    > 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@cisco.com>
    >> ---
    >> 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
    >

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