Re: [PATCH 1/7] kernel: don't call do_exit() for PF_IO_WORKER threads

Eric W. Biederman
2021-03-26T20:45:26Z

Jens Axboe <axboe@kernel.dk> writes:

> Right now we're never calling get_signal() from PF_IO_WORKER threads, but
> in preparation for doing so, don't handle a fatal signal for them. The
> workers have state they need to cleanup when exiting, and they don't do
> coredumps, so just return instead of performing either a dump or calling
> do_exit() on their behalf. The threads themselves will detect a fatal
> signal and do proper shutdown.
>
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> ---
> kernel/signal.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/kernel/signal.c b/kernel/signal.c
> index f2a1b898da29..e3e1b8fbfe8a 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -2756,6 +2756,15 @@ bool get_signal(struct ksignal *ksig)
> */
> current->flags |= PF_SIGNALED;
>
> + /*
> + * PF_IO_WORKER threads will catch and exit on fatal signals
> + * themselves. They have cleanup that must be performed, so
> + * we cannot call do_exit() on their behalf. coredumps also
> + * do not apply to them.
> + */
> + if (current->flags & PF_IO_WORKER)
> + return false;
> +

Returning false when get_signal needs the caller to handle a signal
adds a very weird and awkward special case to how get_signal returns
arguments.

Instead you should simply break and let get_signal return SIGKILL like
any other signal that has a handler that the caller of get_signal needs
to handle.

Something like:
> + /*
> + * PF_IO_WORKER have cleanup that must be performed,
> + * before calling do_exit().
> + */
> + if (current->flags & PF_IO_WORKER)
> + break;

As do_coredump does not call do_exit there is no reason to skip calling into
the coredump handling either. And allowing it will remove yet another
special case from the io worker code.

> if (sig_kernel_coredump(signr)) {
> if (print_fatal_signals)
> print_fatal_signal(ksig->info.si_signo);

Eric