Date: Tue, 4 Aug 2015 17:53:11 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Luigi Rizzo <rizzo@iet.unipi.it> Cc: freebsd-current <freebsd-current@freebsd.org>, Stefano Garzarella <stefanogarzarella@gmail.com>, Giuseppe Lettieri <g.lettieri@iet.unipi.it> Subject: Re: proper way to terminate a kthread when the parent process dies ? Message-ID: <20150804145311.GN2072@kib.kiev.ua> In-Reply-To: <CA%2BhQ2%2Bg8zSSHrLFiuD3-oZ1D0F9BsnJKVwc0hSDowr4gaX6eYw@mail.gmail.com> References: <CA%2BhQ2%2Bg8zSSHrLFiuD3-oZ1D0F9BsnJKVwc0hSDowr4gaX6eYw@mail.gmail.com>
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On Tue, Aug 04, 2015 at 04:38:14PM +0200, Luigi Rizzo wrote:
> Hi,
> we have a doubt on the proper way to terminate a kernel thread that
> has been associated to a user process U within a system call with
>
> kthread_add( .. , .., p, ... )
>
> (p is the struct proc * of the calling process, U)
>
> When U terminates and goes into kern_exit.c :: exit1()
> the kernel thread sees the following conditions:
>
> P_SHOULDSTOP(td->td_proc) is TRUE
>
> td->td_flags has TDF_ASTPENDING | TDF_NEEDSUSPCHK set
>
> We are not sure what is the proper way to terminate
> our kernel thread, whose body is the following:
>
> while (must_run) { // someone will set must_run = 0
> <check_for_forced_termination>
> kthread_suspend_check(); // void
> work_or_short_tsleep(); // potentially se
> }
> kthread_exit();
>
> We have seen different ways for the <check_for_forced_termination>
>
> 1. if (P_SHOULDSTOP(td->td_proc)
> break; // kthread_exit() is called outside the loop
>
> 2. if (P_SHOULDSTOP(td->td_proc)
> thread_suspend_check(0); // which then terminates the thread
> // this is done in sys/rpc/svc.c
>
> We are a bit unsure whether calling the thread_*() function in a kthread
> is correct -- but there is an example in the kernel.
>
> Variants involve locking td->td_proc (but is it necessary ? The process
> won't go away until all child threads die), or checking the td_tdflags
> instead of the parent process' flags.
>
> So what is the correct way ?
If this is a thread of the normal user process, then it is not a kernel
thread, even if it never leaves the kernel mode.
You must call thread_suspend_check() in any in-kernel loop to allow the
stops and process exit to work.
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