Re: [PATCH 02/10] exit: Add and use make_task_dead.

Eric W. Biederman
2022-01-05T20:46:28Z

Al Viro <viro@zeniv.linux.org.uk> writes:

> On Wed, Dec 08, 2021 at 02:25:24PM -0600, Eric W. Biederman wrote:
>> There are two big uses of do_exit. The first is it's design use to be
>> the guts of the exit(2) system call. The second use is to terminate
>> a task after something catastrophic has happened like a NULL pointer
>> in kernel code.
>>
>> Add a function make_task_dead that is initialy exactly the same as
>> do_exit to cover the cases where do_exit is called to handle
>> catastrophic failure. In time this can probably be reduced to just a
>> light wrapper around do_task_dead. For now keep it exactly the same so
>> that there will be no behavioral differences introducing this new
>> concept.
>>
>> Replace all of the uses of do_exit that use it for catastraphic
>> task cleanup with make_task_dead to make it clear what the code
>> is doing.
>>
>> As part of this rename rewind_stack_do_exit
>> rewind_stack_and_make_dead.
>
> Umm... What about .Linvalid_mask: in arch/xtensa/kernel/entry.S?
> That's an obvious case for your make_task_dead().

Good catch.

Being in assembly it did not have anything after the name do_exit so it
hid from my regex "[^A-Za-z0-9_]do_exit[^A-Za-z0-9]". Thank you for
finding that.

Skimming the surrounding code it looks like Linvalid_mask can only be
reached by buggy hardware or buggy kernel code. If userspace could
trigger the condition it would be a candidate for force_exit_sig.

I am a bit puzzled why die is not called, instead of die being
handrolled there.

xtensa folks any thoughts?

If not I will queue up a minimal patch to replace do_exit with
make_task_dead.

Eric