Re: [PATCH v2 2/2] pidfd: change pidfd_send_signal() to respect PIDFD_THREAD

On 02/20, Christian Brauner wrote:

On Fri, Feb 16, 2024 at 07:12:14PM +0100, Oleg Nesterov wrote:

quoted

On 02/16, Christian Brauner wrote:

quoted

quoted

SI_USER means that the target can trust the values of si_pid/si_uid
in siginfo.

Bah, what an annoying nonsense. I see that this can be used to emulate
stuff like SI_TIMER and SI_ASYNCIO. But I very much doubt the value of
e.g., emulating SI_DETHREAD. Maybe I'm missing something very obvious.

I don't understand...

My question was what the purpose of being able to to set si_code to
e.g., SI_DETHREAD is and then to send a signal to yourself? Because it
looks like that's what rt_{tg}sigqueueinfo() and pidfd_send_signal()
allows the caller to do. I'm just trying to understand use-cases for
this.

Ah. IIRC criu uses this hack to restore the pending (arbitrary) signals
collected at dump time.

I was a bit surprise sys_pidfd_send_signal() allows this hack too, I don't
think that criu uses pidfd at restore time, but I do not know.

Oleg.