On Thu, 14 Mar 2019 21:36:43 -0700 Daniel Colascione <dancol@xxxxxxxxxx> wrote: > On Thu, Mar 14, 2019 at 8:16 PM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > > > On Thu, 14 Mar 2019 13:49:11 -0700 > > Sultan Alsawaf <sultan@xxxxxxxxxxxxxxx> wrote: > > > > > Perhaps I'm missing something, but if you want to know when a process has died > > > after sending a SIGKILL to it, then why not just make the SIGKILL optionally > > > block until the process has died completely? It'd be rather trivial to just > > > store a pointer to an onstack completion inside the victim process' task_struct, > > > and then complete it in free_task(). > > > > How would you implement such a method in userspace? kill() doesn't take > > any parameters but the pid of the process you want to send a signal to, > > and the signal to send. This would require a new system call, and be > > quite a bit of work. > > That's what the pidfd work is for. Please read the original threads > about the motivation and design of that facility. I wasn't Cc'd on the original work, so I haven't read them. > > > If you can solve this with an ebpf program, I > > strongly suggest you do that instead. > > We do want killed processes to die promptly. That's why I support > boosting a process's priority somehow when lmkd is about to kill it. > The precise way in which we do that --- involving not only actual > priority, but scheduler knobs, cgroup assignment, core affinity, and > so on --- is a complex topic best left to userspace. lmkd already has > all the knobs it needs to implement whatever priority boosting policy > it wants. > > Hell, once we add a pidfd_wait --- which I plan to work on, assuming > nobody beats me to it, after pidfd_send_signal lands --- you can > imagine a general-purpose priority inheritance mechanism expediting > process death when a high-priority process waits on a pidfd_wait > handle for a condemned process. You know you're on the right track > design-wise when you start seeing this kind of elegant constructive > interference between seemingly-unrelated features. What we don't need > is some kind of blocking SIGKILL alternative or backdoor event > delivery system. > > We definitely don't want to have to wait for a process's parent to > reap it. Instead, we want to wait for it to become a zombie. That's > why I designed my original exithand patch to fire death notification > upon transition to the zombie state, not upon process table removal, > and I expect pidfd_wait (or whatever we call it) to act the same way. > > In any case, there's a clear path forward here --- general-purpose, > cheap, and elegant --- and we should just focus on doing that instead > of more complex proposals with few advantages. If you add new pidfd systemcalls then making a new way to send a signal and block till it does die or whatever is more acceptable than adding a new signal that changes the semantics of sending signals, which is what I was against. I do agree with Joel about bloating task_struct too. If anything, have a wait queue you add, where you can allocate a descriptor with the task dieing and task killing, and just search this queue on dying. We could add a TIF flag to the task as well to let the exiting of this task know it should do such an operation. -- Steve _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
