Date: Tue, 4 Aug 2015 17:32:28 +0200 From: Luigi Rizzo <rizzo@iet.unipi.it> To: Konstantin Belousov <kostikbel@gmail.com> Cc: freebsd-current <freebsd-current@freebsd.org>, Stefano Garzarella <stefanogarzarella@gmail.com>, Giuseppe Lettieri <g.lettieri@iet.unipi.it>, Luigi Rizzo <rizzo@iet.unipi.it> Subject: Re: proper way to terminate a kthread when the parent process dies ? Message-ID: <CA%2BhQ2%2BiUpK9Z_bV9TYpWQEd0mi=PKtcwNThqg_WYVrka1reBHg@mail.gmail.com> In-Reply-To: <20150804145311.GN2072@kib.kiev.ua> References: <CA%2BhQ2%2Bg8zSSHrLFiuD3-oZ1D0F9BsnJKVwc0hSDowr4gaX6eYw@mail.gmail.com> <20150804145311.GN2072@kib.kiev.ua>
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On Tue, Aug 4, 2015 at 4:53 PM, Konstantin Belousov <kostikbel@gmail.com> wrote:
> 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.
thanks for the answer.
i do not really know what is the difference between a "kernel thread"
and a "thread".
Could you clarify what is the distinctive feature between the two ?
Perhaps being owned by pid 0 ?
This specific thread is created within a system call by invoking kthread_add()
and associated with the user process.
>
> You must call thread_suspend_check() in any in-kernel loop to allow the
> stops and process exit to work.
so does it mean that the kthread_suspend_check() is incorrect and we should
use thread_suspend_check() instead ?
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
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