Re: [PATCH] ptrace: exit: re-trigger PTRACE_EVENT_EXIT after coredump finished

From: Eric W. Biederman
Date: Mon Nov 22 2021 - 10:02:36 EST

Vladimir Divjak <vladimir.divjak@xxxxxx> writes:

> (if one is requested with PTRACE_SEIZE setting PTRACE_O_TRACEEXIT option)
> for a process being core-dumped, after the coredump is finished.
> This enables a potential tracer - coredump user mode helper
> (or any other tracer started after the coredump was initiated)
> to receive the PTRACE_EVENT_EXIT for all threads of the crashing process.
> Rationale:
> For zapped threads, PTRACE_EVENT_EXIT is triggered early during do_exit(),
> before the point at which they sleep, waiting for
> coredump to finish - in exit_mm(), and before a potential
> coredump user mode helper process is launched.
> That makes it impossible for the coredump user mode helper process to
> receive PTRACE_EVENT_EXIT events for all threads of the crashing process,
> except for the thread handling the core-dump, which will trigger
> the PTRACE_EVENT_EXIT after the coredump has been finished.

Please test the latest kernel.

The coredump now stops much earlier than exit_mm, and PTRACE_EVENT_EXIT
is after the point the coredump stops.

If you need this functionality on older kernels it should be possible to
backport a subset of my changes without too much trouble