Date: Tue, 4 Aug 2015 16:38:14 +0200 From: Luigi Rizzo <rizzo@iet.unipi.it> To: freebsd-current <freebsd-current@freebsd.org> Cc: Luigi Rizzo <rizzo@iet.unipi.it>, Stefano Garzarella <stefanogarzarella@gmail.com>, Giuseppe Lettieri <g.lettieri@iet.unipi.it> Subject: proper way to terminate a kthread when the parent process dies ? Message-ID: <CA%2BhQ2%2Bg8zSSHrLFiuD3-oZ1D0F9BsnJKVwc0hSDowr4gaX6eYw@mail.gmail.com>
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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 ?
cheers
luigi
--
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Prof. Luigi RIZZO, rizzo@iet.unipi.it . Dip. di Ing. dell'Informazione
http://www.iet.unipi.it/~luigi/ . Universita` di Pisa
TEL +39-050-2217533 . via Diotisalvi 2
Mobile +39-338-6809875 . 56122 PISA (Italy)
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