Re: [PATCH 0/9] Refactoring exit

Al Viro [off-list ref] writes:

On Thu, Jun 24, 2021 at 01:57:35PM -0500, Eric W. Biederman wrote:

quoted

So far the code has been lightly tested, and the descriptions of some
of the patches are a bit light, but I think this shows the direction
I am aiming to travel for sorting out exit(2) and exit_group(2).

FWIW, here's the current picture for do_exit(), aside of exit(2) and do_exit_group():

1) stuff that is clearly oops-like -
        alpha:die_if_kernel() alpha:do_entUna() alpha:do_page_fault() arm:oops_end()
        arm:__do_kernel_fault() arm64:die() arm64:die_kernel_fault() csky:alignment()
        csky:die() csky:no_context() h8300:die() h8300:do_page_fault() hexagon:die()
        ia64:die() i64:ia64_do_page_fault() m68k:die_if_kernel() m68k:send_fault_sig()
        microblaze:die() mips:die() nds32:handle_fpu_exception() nds32:die()
        nds32:unhandled_interruption() nds32:unhandled_exceptions() nds32:do_revinsn()
        nds32:do_page_fault() nios:die() openrisc:die() openrisc:do_page_fault()
        parisc:die_if_kernel() ppc:oops_end() riscv:die() riscv:die_kernel_fault()
        s390:die() s390:do_no_context() s390:do_low_address() sh:die()
        sparc32:die_if_kernel() sparc32:do_sparc_fault() sparc64:die_if_kernel()
        x86:rewind_stack_do_exit() xtensa:die() xtensa:bad_page_fault()
We really do not want ptrace anywhere near any of those and we do not want
any of that to return; this shit would better be handled right there and
there - no "post a fatal signal" would do.

Thanks that makes a good start for digging into these.

I think the distinction I would make is:
- If the kernel is broken use do_task_dead.
- Otherwise cleanup the semantics by using start_group_exit,
  start_task_exit or by just cleaning up the code.
  

Looking at the reboot case it looks like we the code
should have become do_group_exit in 2.5.  I have a suspicion
we have a bunch of similar cases that want to terminate the
entire process, but we simply never updated to deal with
multi-thread processes.

I suspect in the reboot case panic if machine_halt or
or machine_power_off fails is more likely the correct
handling.  But we do have funny semantics sometimes.

I will see what I can do to expand my patchset to handle all of these
various callers of do_exit.

Eric