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:

quoted

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 <redacted>
---
 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